# S10 Brakes!!



## Murray (Dec 17, 2001)

HELP!!
I live in Scotland, I bought a 1987 Blazer S10, 2.8 manual with soggy brakes, thinking I could cure them easily - WRONG!! With a lot of help from Alan in Vt., I have changed the calipers, wheel cylinders, master cylinder, pads shoes and hardware, and STILL soggy brakes! I've bled and re-bled this thing, but no improvement. The only thing in there that's not brand new is the proportioning valve. Could that be the problem? The pedal sinks pretty far with the engine running, about 5-6" before any resistance is felt. My friend has the same fault on three S10's. Do these things all have bad brakes? Is it the valve? There's nowhere over here to take the car to, mostly I do the work myself, but this has got me beat.


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## plowking35 (Dec 21, 1999)

the valve could have defaulted, but I would look into the booster as well.
Dino


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## Murray (Dec 17, 2001)

Thanks, but I looked into the booster, and it seems okay. The pedal is still not perfect without the engine running, but is better. Start her up and the pedal becomes much lighter, implying the booster is working. Also, pumping the pedal brings the revs up as the vacuum is depleted. Sheare Chevrolet say it sounds like the valve, but say I need to pressure bleed the system - PROBLEM! How do you get a seal on the master? I drilled the top from my spare master, and fitted it up with the tube from a pressure bleeder, but even with a half dozen cable ties holding the lid on, fluid and pressure escape everywhere!Back to the drawing board. Any suggestions?


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## DaveK (Jul 9, 2001)

Make sure the rear brakes are adjusted correctly. Whenever the pedal is low, that is the first thing to check. Spongy pedal is not the same as a low pedal.


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## Murray (Dec 17, 2001)

Thanks, but new adjusters fitted, and set as snug as the drums will allow.
Told you it was a hard one!!


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## DaveK (Jul 9, 2001)

I know you won't want to hear this but I have gotten bad master cylinders right out of the box. 
Once you are confident that all the air is out of the system, which could be quite a bit with new calipers, master and wheel cylinders, everything points to the master cylinder.

The proportioning valve (really a combo valve) won't effect pedal travel. It warns you when you lose front or rear brakes through the brake warning light. It applies pressure to rear brakes slightly before the front. And it gives the rear brakes a lower percentage of breaking power than the front. None of which, if not working correctly, would give the symtoms you have now.


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## Alan (Mar 2, 2000)

What Murray is going through is very similar to the ordeal I've been having with my 88 S pickup. So far the dealer has replaced just about everything but the lines on this one and still no rear brakes. We had a serious discussion about the bill I got with no results and the attitude of the wisea$$ service manager. They settled for parts and labor at actual cost rather than find the problem as opposed to throwing parts at it.

Front brakes work so-so at this point, rears are a joke. Shoes are adjusted very tight and are in new drums and on new backing plates. Stuffing the pedal to the floor and blipping the throttle will spin the rear wheels with no load on the drivetrain. With the rear jacked up and wheels turning at 30 or so, pound the brake pedal and you can watch the wheels slow down, not an alomst instant stop like there should be.

I haven't found time to hook up the power bleeder yet, but that's getting close to the top of the project list. Hopefully that will produce results.


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## thelawnguy (May 20, 2001)

I would replace the rubber lines (two in front and one at the axle). Cheap, but if they are soft they will expand rather than send pressure to the cylinders.


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## Alan (Mar 2, 2000)

Done that too!


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## DaveK (Jul 9, 2001)

Alan, didn't the dealer power bleed them?


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## Alan (Mar 2, 2000)

I'm not sure just how they did bleed them, I never asked. But, in light of some of the workmanship issues I tend to doubt they HAVE a power bleeder. They replaced both lines across the rear axle,, with stock lengths of tubing, then made a big "U" bend out of the excess and tucked that down UNDER the axle, on a 4x4, no less. What a wonderful place to snag them! Makes me wonder if they have a flaring tool and/or the ability to make a line to the right length.


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## DaveK (Jul 9, 2001)

Oh, that type of dealership. Just be glad they weren't putting an exaust pipe on. It's kinda hard to make loops with that. lol


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## CT18fireman (Nov 30, 2000)

Not sure if one exists on the s-10 but I had the problem with the load sensing valve on my Toyota. This is a valve on the rear end that when the bed settle from a load changes pressures sent to the rear brakes. After replacing the lines I had to bleed and reset mine so that I got rear brakes and a solid pedal.


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## John DiMartino (Jan 22, 2000)

S10's do not have a load sensing valve,Alan,did you put a new proportining valve on?If not do it,if that isnt it,Id put a hydraulic pressure guage on the rear wheel port,I betyou master cyl isnt developing the pressure it should.How does the E-brakes work,will they lock up the rear wheels?,if not the shoes may be glazed over,Ive had brand new brakes hoes,that for wahtever reason,wouldnt stop the truck,im not sure if compound was wrong,or what.I put Geniune GM shoes on out of frustration,and problem solved,those Gm brakes shoes/pads are $$,but they seem to stop the truck better than the rest.If your master checks out strong,Id go with a manual,adjustable proporting valve,you can get them from Summit racing,mount it undrt the cab,you will be able to adjust the rear brakes for more bias,when you have lot of weight in the back.One other thing,do you have at least 500 miles on the brakes,since the new drums,and shoes were replaced,Ive found it takes that long sometimes to get them to work to their full potential,they need to be bedded in.


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## Murray (Dec 17, 2001)

A couple of questions, guys. First, does anyone have a method of sealing the pressure bleeder onto the master? I'm going to try and make something up, with a couple of pieces of steel bar, one top, one below, a couple of screwed rods to clamp the whole thing, and I will try to make up a rubber plug with the pipe from the bleeder through it that will sit on the orifice in the bottom of the reservoir for the master. Next, can I bleed one side at a time, rears then fronts? If not, then my method is not going to work. And lastly, to prove the valve at fault, could I just put the lines straight to the master, at the risk of too much pressure at the rears? If so, I guess I could learn to drive with that!Thanks for the tips so far.


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## Knightcrawler (Dec 23, 2001)

*spongy s-10 brakes*

did you see if the vacume hose coming off your booster is cracked or split and isnt leaking from the tbi, whenever i lower an s-10 this becomes a problem and a new hose must be placed on then clamped tight or the exact thing you describe will hapeen


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## Murray (Dec 17, 2001)

I'm pretty sure there's no vacuum leak, but not certain. I did have one when I changed the PCV, and although I didn't notice it on the brake pedal, the engine was revving to about 2500 rpm, and the 4-wheel to 2-wheel shifter was taking an age to react. I will have another look when it gets light out, though. Thanks.


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## DaveK (Jul 9, 2001)

A leak in the booster line will make the pedal a little firmer when applying the brakes. And you would probably be able to tell by simply stepping on the brakes. Kinda like using the brakes when the engine isn't running.

I just thought of another posibility. There is an adjusment (not totally sure on the S10) for the gap (or lack of) between the rod that applies pressure and the piston in the master cylinder. If it is adjusted to far, it wouldn't let the piston return fully to the normal state. If the gap is to large, the pedal would move quite a distance before beginning to apply the brakes. 

This is just another theory, but hey, you are running out of options. 

And remember, I do know that on some vehicles it is adjustable, but I am not 100% sure on the S10, so don't go breaking anything trying to adjust something that can't be adjusted. 

Dave


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## plowjockey (Dec 3, 2000)

When I used to set the e-brakes on the S-10's on the line at GM we would depress the e-brake pedal to a pre-determined point and then pull out or back on the brake pedal to set the booster rod length. This was when the boosters had just been installed and the engine had not as of yet been started. I don't know if this would work on a vehicle that had been used or not.

Bruce


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## staley52 (Dec 17, 2001)

Ok former GM tech here 

first off it is not the booster if there was a booster problem the pedal would be hard not soft

next for those of you using a preasure bleeder do not use more than 10 to 12 psi you will get a better and faster bleed, and not blow off your cap

next can you pump the crap out of the brakes and get a good pedal feeling and brakes at all 4 if you can there is 2 options there is air in system or a bad proportioning valve this prosess will also eliminaate the hoses doing this will usually blow any soft hoses now if the pedal only improves slightly or not at all you have a bad master on one car I had to install 2 remans then 2 new units with the 2nd new one working to get brakes

One thing that I hope is common knowlege is do not mix brake fluid use the recomended fluid i.e. dot 4 if you mix it has been known to eat seals espesialy dot 5 in a 3 or 4 system 
now you can up grade from dot 3 to 4 but not to 5 just be sure to flush out all the 3 and I repeat do not use dot 5 unless specificly called for in manual and s10's don't call for it


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## plowjockey (Dec 3, 2000)

Staley

I had always been told that if you mixed dot 3 and dot 5 it would turn somewhat to a gell. Is that correct?

You make a very good point.

Bruce


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## DaveK (Jul 9, 2001)

> first off it is not the booster if there was a booster problem the pedal would be hard not soft


 I've said the same thing. A bad vacuum line or other booster vacuum problem would just effect pedal pressure.

I also said that while they don't want to hear it, a "new" master cylinder CAN be bad.

Staley, What is your opinion on my last given theory about the booster rod length being "out of whack" and not letting the piston in the master cylinder return fully to the normal state?

BTW Staley, welcome to plowsite.


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## staley52 (Dec 17, 2001)

I have rarely come across a push rod adjustment problem the only time that I have adjusted them is when replaceing boosters when replacing master cyinders I never adjust the machining of the master cylinders are almost always identicle. pehaps if they put the incorrect master on the truck the push rod may be off but this is NOT fixed with adjustment it is fixed with the correct part.


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## Murray (Dec 17, 2001)

Guys, my dad was over or Christmas dinner today, and he says if the new front to rear pipe is the wrong diameter, it could effect the pedal travel, but not the brake pressure. If you replace steel lines with copper, the I.D. size is different, due to the copper lines being thicker walled. I have my home-made pressure bleeder home from work, and will try it out hopefully at the weekend, weather permitting. I asked the question a couple of days ago, what if I bypass the proportioning valve altogether, will that fix the poor pressure problem, or what? Even if the back brakes lock up in anger, I could live with that if the car stops!! There must be a way to prove the master on the car, to see if it's faulty, rather than just guessing. If I have a pedal which is firm, if a bit " rubbery" without the engine running, then light with the engine running, then the booster is okay, but what about the master, is there some test on it? The Chevy dealer says on the phone the proportioning vaslve is not worth changing, it would still need pressure bled to reset the valve, even a new one. Keep the info coming, guys, I need to lick this!!
Merry Christmas from Scotland!! Cheers!


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## CT18fireman (Nov 30, 2000)

This is true because you would be moving more or less volume of fluid at the same pressure. Any firefgihter knows that a larger hose size will move more water at the same pressure as a smaller line.


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## thelawnguy (May 20, 2001)

I would never EVER use copper for brake lines...


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## John DiMartino (Jan 22, 2000)

Bill is right,not copper,not ever,not for fuel,or especially brake lines,it fatigues easier the steel,is way to soft for high pressure,and will crack around the fittings over time.


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## DaveK (Jul 9, 2001)

A different size line will not effect pedal travel.

You are displacing a certain amount of fluid in the master cylinder which is transferred to the calipers and wheel cylinders. You could run it into and out of a 50 gallon drum and you are still displacing the same amount of fluid at both ends. 

And take the copper lines off!
And if you have replaced any rubber lines, make sure they were made for brakes.


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## Murray (Dec 17, 2001)

Guys, all our replacement brake lines in this country are manufactured from a copper-alloy tube, it's all you can buy at the motor factor outlets. I would disagree that these lines will fracture, as the material is much more maleable than steel lines, and far less likely to puncture with an impact. Unless we buy a new line from the manufacturer, there's no choice! Does anyone know of a way to test this master cylinder on the car, other than the fact that the brakes are crap? I appreciate it could be faulty, but surely the majority that are remanufactured are good. All the rubber line are for brakes, and they are NOT expanding with the pressure.Also, just how bad is the thing without theproportioning valve? can I try the car without it?


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## John DiMartino (Jan 22, 2000)

By copper,we mean the copper tubing you buy in rolls,at the hardware store,this stuff isnt any good,Ive seen it used,and had to repair a few patches that cracked.Call the brake lineswhat you want,Im not a steel expert,but i can tell you the lines i put on are not copper,if they are,its such a small percentage.The replacement lines rust thru in 4-5 years,copper wouldnt do that.These are the same lines everyone else is buying, i hope.


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## Murray (Dec 17, 2001)

Hey, I'm not trying to offend anyone, I,m just saying that in the U.K., standard replacement brakeline is of a copper alloy, and is the only available material, even from the dealer. My questions are still these; 1- how bad would the brakes be with the proportioning valve out of the loop, and 2- Is there a way of testing the master cylinder on the car, other than just to say if the brakes are crap, it must be the master?There is an improvement in the brakes with a few pumps of the pedal, so it would suggest that there was air in there, the only place it could be hiding is the proportioning valve. Hopefully with this pressure bleeder, I will shift it, but my next course of action would have been to by-pass the proportioning valve, and put the lines straight to the master. If I still didn't get anywhere, I guess that would suggest the master. I was just wondering if there was a sure-fire way of proving any of these components. Alan has this same thing, and he's changed the proportioning valve on his!


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## DaveK (Jul 9, 2001)

You could put a gauge on the rear line and check the master that way. I am not sure what pressure reading you should have though.


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## Murray (Dec 17, 2001)

I guess a guage would show if there was very little pressure to the rear, but I know that there is a bit of pressure, if you hold down on the pedal, then get someone to open the bleeder, it does kinda squirt out, but whether there is the pressure there should be, is anyone's guess.Is there a widely available brake line kit for these cars at the parts houses or dealers?One with the lines already made up, rolled up in a bag or box, with the flexibles and tee-pieces too? I guess I've come this far, and I want to keep the Blazer when this is fixed, if I changed all the lines together with the proportioning valve, then we would have a complete new system on there. I would rather use the lines you guys are talking about, if you think the ones available here are no good.
Thanks.


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## thelawnguy (May 20, 2001)

If you go to the dealer, GM stocks incremental lengths of flared steel tubing, its the techs responsibility to bend it to match the old, or follow the diagram in the service manual. They do not supply pre-formed brake line as service replacement.


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## Murray (Dec 17, 2001)

Guys,I had a go at bleeding the system on Sunday, and my home-made pressure set-up worked a treat! Only trouble is that even with the bleeder hooked up to a spare wheel, with about 30 psi in it, there was only a trickle at the rear bleed nipples. That tells me there's a restriction in the system somewhere, and it's not the master. The front brakes have the fluid spraying out no problem, and while it's a smaller bleed nipple at the rear, it should still be better than it is.It could well be a faulty end on the pipe that's under there, I don't trust the workmanship of the guy who did it for me. Why is it that if you want something doing, you have to do it yourself? It smarts when you pay someone hard earned cash to botch something up! Alan is going to price me the nuts and other hardware to change all the lines, but I guess I'll stick with the copper-based lines we have over here- I don't fancy trying to ship a 15' length of brake pipe in one piece!
Happy New Year to all, best wishes for 2002 from Bonny Scotland!!


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## Chuck Smith (Dec 30, 1999)

*Copper???*

Copper????? For BRAKE lines??? No, no, no.... Copper is soft enough to flex. That may be your problem. Up front, short runs, not as much pipe to flex. Going to the rear, much more pipe, more flex. Copper and aluminum tubing have no place on vehicles. At least not according to ASME.

Brake line comes in 6' lengths.

~Chuck


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## Murray (Dec 17, 2001)

Hey, this debate on the brakeline material is an aside from the original questions, Chuck. Thanks for your concern about this, but really, this stuff is under about every car more than five years old in this country. In the U.K., this is the material of choice, and talking to a friend who although he doesn't work on brake systems, has sold and given technical help in all kinds of industrial hydraulic systems, and he assures me this stuff is stamped for over 200 Bar, that is approximately 2900 psi. burst pressure. This is the same stuff you will get fitted to your car in any shop in the U.K., unless you have a current model and specify an original steel line, although who would, as it has rusted through in the few years you owned the car. Now, original questions, can I run this car without the proportioning valve, and is there a common problem with S10 brakes as they get on a bit, as Alan also has three vehicles with very poor brakes. Is there a fault common to these cars? Recap; new calipers, new wheel cylinders, new master new shoes and pads, front brakes not bad, rear brakes not good,pedal still spongey. These copper lines are not the problem, or the last half dozen cars I have owned, including the one my wife is on her way to work in, a 1989 Nissan Bluebird, would have the same problem, and take it from me, the Bluebird has about the best brakes I ever owned. They are way better than the 1995 Rover Vitesse I have, which has ABS. Hey, I'm not making this stuff up, this is the only material used over here in the U.K.! Let's look for the problem please! Thanks.


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## plowking35 (Dec 21, 1999)

Ok, I have the skinny for you guys with the poor s-10 rear brakes.
First off you are not alone, very common problem. 
You guys are also on the right track with the porportioning valve being the culprit. the fix that was relayed to me, was to remove 1 1/2 turns of the coil that is in the brake line aft of the valve. that should help increase line pressure. If that doesnt work, an aftermarket valve may be the answer, one from Wildwood or from a race car parts company make work. They also have adjustable units, that you can control the line pressure from the cab. They use them in NASCAR to help with brake bias going into the corners.
All this was relayed to me by a mechanic whom I implisitly trust, and who has fixed many of these exact problems with s-10's
he also mentioned bring the truck to a dirt drive and at 10 mph or so, stomp the pedal and see if the rears lock up, if they do, you should be ok.
Dino


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## CT18fireman (Nov 30, 2000)

I don't know how removing length of tube would change the pressure. Although it would change the amount of time (very small) that it takes for the pressure to get to the brakes.


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## DaveK (Jul 9, 2001)

My thoughts are the same as CT18fireman.  

An alternative would be to move the rear axle a few inches forward, so that the line will be shorter. You may want to check the muffler bearings and flux capacitor as well.


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## plowking35 (Dec 21, 1999)

Just like with water pressure the longer the run, then more pressure you lose. In two stories home, it is common to use 3/4" supply lines in the first floor, but drop to 1/2" to help carry the pressure to the second floor.
Airlines are the same, you can have 90 psi at the regulator, but only 85 at the end of a 50' hose and only 80 after 100' and so on. Capacity is not decrerased only the pressure. Since we are speaking of very small ID tubing, shortening the run will have a distint affect on the pressure being supplied.
So by shortening the length of brake line to the rear wheel cyl, it will help keep the pressure being fed to them from dropping off. Not so much as acutally increasing the pressure. However the end result will be same. Better brakes.
If it was me, I would replace the valve, but the shorter brake line may work.
Dave K while you have tried to be ammusing, all you have done is to make light of a proper and possibly correct solution to this problem.

Dino


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## CT18fireman (Nov 30, 2000)

I don't think you could remove enough line to make a pressure difference and still meet the reat brakes. Pressure drop would barely be measurable at that distance. Pressure drop occurrs over larger distances. 

In every service manual I have just looked at, Ford and Toyota I cannot see a difference in pressure between a long and shortbed truck. I also notice looking at my Toyota that the single line to the rear comes down the passenger side. Then at the rear axle there is a short rubber line to the brake while the drivers side has a longer tube to it. Your theroy would mean that the driver's side brake would have less pressure. That would mean passenger side brakes would wear faster or lock-up quicker and I have never found that to be true.


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## plowking35 (Dec 21, 1999)

Well you see that is problem with therory and practice. you are therorizing that it wont work, where as the person who relayed this to me has practice that it does work.
Much like you theorize that u edges wont scrape as good as steel, yet many who have used the edges have practice that they do.
If you have a better, or at least any advise to HELP with this dilema, then please step forward. If not, then dont pick apart a possible solution unless you can definatly back up your doubts. reading manuals, having alot of "book" knowledge most often doesnt apply in the real world.
If nothing else, the proportional valve is the likely culprit, and shortening the line may have more to do with getting more line pressure through the valve then because the line is shorter. I dont have an answer for that, but I do know that the person who explained this to me is one of the most knowledgeable mechanics i have ever met, and to add that he has repaired this problem in at least 10 s-10s means to me that it at least has enough merit to try it.
Dino


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## DaveK (Jul 9, 2001)

Tried? I thought I succeded in being amusing. 

First of all, compressed air is in no way the same as hydraulic pressure. But, you could have a 200 ft, or even 2000 ft. hose and would have the *same exact pressure* at the end as you do at the source (provided you have no leaks along the way). With a longer hose, you will have less air flow volume is all.

As far as vertical water lines in a house, that's totally different. You have to overcome gravity in that example. You have the weight of the water providing pressure in the opposite direction. And going from 3/4" to 1/2" lines does not change the pressure. What it does do is cause the water to move through the line faster.

In a "very small ID tubing" in a hydraulic system (which doesn't compress like air), shortening the line, will have absolutely no effect on the pressure at the wheel cylinders. And that is not theory.

In support of CT18fireman,


> Well you see that is problem with therory and practice. you are therorizing that it wont work, where as the person who relayed this to me has practice that it does work.


 I don't think that one rear brake line being longer than the other is a theory. It's a fact on most vehicles. And if a few inches of line made ANY significant difference, the master cylinder would not be located nearly two feet closer to the left side of the vehicle.

As far as the most knowledgeable mechanic, one solution (shortening the line) is hilarious. The other solution (after market race car proportioning valve) doesn't fix the problem. It fixes the symptom. Kind of like adding nitrous to your car because it has less power than it did last week. Sure nitrous will give you the power back, but it has nothing to do with the original loss of power.

I think your "mechanic" needs a little more "book" knowledge.


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## chevroletwizard (Jan 8, 2002)

plowking, i think i am gonna have to go with your side on this pressure debate. being a farm boy, and around diesel tractors. out of the injection pump come all the fuel lines going to each cylinder's injector. all of the fuel lines are the same length . reason ..... to keep fuel pressure the same across the board. hydralics just means fluid, whether it is water, fuel ,oil , it is hydralics. hydralics will not compress, such as air. but shortening the lines may be very minimal difference also, so i can see that point, my point is that the length of the lines does make a difference in pressure, how much?? who knows without setting up a test on a bench.


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## DaveK (Jul 9, 2001)

> all of the fuel lines are the same length . reason ..... to keep fuel pressure the same across the board.


 And can you explain why the left front brake line is a couple feet shorter than the right? If you are gonna use a theory, use a good one.



> hydralics just means fluid, whether it is water, fuel ,oil , it is hydralics. hydralics will not compress, such as air."


 Thanks for science lesson in hydra*u*lics.


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## chevroletwizard (Jan 8, 2002)

it not a therory it is fact, in the fuel injection system the concern is about precision, i am sure that the difference in pressure is minimal like i stated. all i was saying is that the line length has an effect on pressure( fact) now for the therory. i would tend to believe that the pressure difference is so minimal it doesnt make any difference in the braking system, since it isnt as precision as a fuel injection system is, i really doubt that they would worry about a fraction of a psi difference from one side to the other for the brakes


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## Murray (Dec 17, 2001)

JEEZ!!!
You guys, sorry for disapearing, but my ISP has not been mailing me to let me know there are fresh entries to this thread, and boy are there!!
I am pretty certain that there are a couple of factors to my poor brakes.1. I think the proportioning valve is definitely worth changing, as it is the link between front and rear, 2. I can see the pipe length thing too, especially as we are talking, are we not, about the pipe at the master end,i.e. the common line for both rears, therefore shortening it by a factor of two, if you see what I mean, less pipe for both rears. And 3. the line on this particular s10 is way smaller than the original, and I have convinced myself that it is also contributing to the pressure, or volume, problem. The guy who changed the line isn't much of a mechanic, and isn't Chevy-conversant, but even I would have fitted like for like!
So please, keep it clean, guys, and thanks for the input, really. You guys are all I got!!
I have decided to re-pipe the whole system, with correct size line, and new flexibles too, just in case that's causing a bit of loss. And the new proportioning valve.
Has anyone heard from Alan? I've been mailing since New Year, and nothing.


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## reallyrusty (Mar 18, 2001)

a Pressure drop can only occurs in an open or flowing system.
fluid has to be in motion. When fluid flow stops (brake pedal down) and pressure builds up, it has to be the same in every inch of the hydraulic system. That's a law of science. Some of the other examples descibed (ie fuel system) are not closed systems.


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## plowking35 (Dec 21, 1999)

Aside from the issue at hand, it is fact that as you add hose to compressed air you lose pressure. I beleive the rule of thumb is about 1 lb per 10'. I used to have a chart but no longer can find it.
However just today I tested this "theory", and with a setting of 90 psi at the regulator, and 100' of hose run out, I had 82 psi at the end of the hose at another gauge. this was 1/4" id hose with 1/4" connectors.


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## DaveK (Jul 9, 2001)

Dino, the only fact is that it wasn't quite a valid test. You used two different gauges. And don't even know if they are accurate. And was this a closed system, or did you have air flowing out of the end? If you were using a air drill (or whatever) then it wasn't a closed system. 

It doesn't matter if the gauge is at the beginning, the middle, or the end, the pressure will be the same. In a closed system, (even compressed air) the presssure will be equal. Think of a tire. The pressure is the same in every spot inside the tire. That is no different than a hose. It is just a different shape.


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## Alan (Mar 2, 2000)

> _Originally posted by plowking35 _
> *
> You guys are also on the right track with the porportioning valve being the culprit. the fix that was relayed to me, was to remove 1 1/2 turns of the coil that is in the brake line aft of the valve. that should help increase line pressure. Dino *


Sorry, but I don't buy into that fix at all. First, I HAVE changed proportioning valves in mine and it made no difference. As for removing roughly 9" of brake line, that totally defies logic. In a closed system like this, whatver fluid you put in one end results in the exact same amount coming out the other end. This is assuming there is NO air in the lines anywhere. Whatever fluid the master pumps end up in the wheel cylinders. If the line length was that critical every vehicle I know of would pull to the left under braking as the right fron wheel has a much longer line than the left does. Also, this 9" difference is less than the difference in lengths of line on a S-Blaxer 2 door and a S pickup long bed. If this theory played out right there would have to be different parts in the brake system in the two examples, and other than lines the parts are the same throughout the system.

I think the muffler bearing and flux capacitor are probably more relevant than 9" of brake tubing.

Besides which, the brakes worked when it left the factory with 9" of line in there.


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## Murray (Dec 17, 2001)

Hey, long time, no hear, right?
Well, a possible cure seems to be lurking under an assumed name, look up " clarification of s-10 brake problems" by PLOWKING, now it makes sense, cutting the spring in the valve, not the line!
I am awaiting parts to allow me to re-pipe the whole system, then be assured, if it is not cured, the spring will be getting cut!!

Thanks everyone for all the input. I will definitely let you know how this turns out!! Thanks again.


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## DaveK (Jul 9, 2001)

I did see the "clarification post". If cutting the spring is a solution, then the proportioning valve should be replaced. The spring didn't simply become to long somehow.....

That's kinda like adding a higher CCA battery because the starter is drawing to many amps. Sure, it's *a* solution, but it isn't *the* solution.


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## CT18fireman (Nov 30, 2000)

I agree with DaveK. Good temporary fix but not the right fix.


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## plowking35 (Dec 21, 1999)

If the problem is line pressure, then by increasing the line pressure it will cure the problem. The valve is preset with to low rear bias, and the only adjustment is by modifying the spring. That way more pressure is given to the rear brakes and not hurting front braking ability.
I was told to start with 1/2 a coil and work it from there.
Unless I hear a better idea from you guys, why doubt its effectiveness.


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## DaveK (Jul 9, 2001)

I don't doubt it's effectiveness. I just question the logic behind it. Instead of cutting a bit off, and trying it, then cutting more and trying it, etc etc. Why not just replalce the valve, if that is in fact the cause.

Getting back to Murray's original problem, it is a spongy and/or low pedal, not that the rears won't lock up, which was Alan's problem. 

So shortening the spring or replacing the valve may cure Alan's truck, but I am not so sure about Murray's truck. 

Murray's trouble could be a few of the things that were mentioned above, but I don't believe that the proportioning valve being "out of adjustment" or bad would give him spongy brakes OR a low pedal.
.


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## Chuck Smith (Dec 30, 1999)

Just get an adjustable proportioning valve from Jegs or Summit Racing. That will solve the "adjustment" problem. 


~Chuck


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## DaveK (Jul 9, 2001)

Aftermarket proportioning valves have already been discussed.



> ....Kind of like adding nitrous to your car because it has less power than it did last week. Sure nitrous will give you the power back, but it has nothing to do with the original loss of power....


Why get an adjustable valve, when you don't need adjustability?


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## John DiMartino (Jan 22, 2000)

Gm's valve isnt set with the correct bias,so use an adjustable one,get the rear brake feel just how you like it,and lock it down,dont ever adjust it again.Now you will be able to stop safely with all 4 wheels stopping you.


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## thelawnguy (May 20, 2001)

Its not just the S-10. Seems all Delco Moraine brake systems are like this. My Dodge Ram had horrible rear braking ability (Delco brake system on it, yes everything is stamped ACDelco) I finally put larger bore rear wheel cylinders from a 3500 on it and its been much much better. My 86 Bonneville is the same way, when its wet or slick out the fronts will lock up very easily in comparison to the rears which seem to be just a holder for the e-brake lol. But my 86 Fury could lock up all 4 sneakers anytime.


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## John DiMartino (Jan 22, 2000)

Your right Bill,the only thing worse on our Dodge's than the Gm rear braking system is the GM steering system,the 2 things on our trucks that are GM give us the most trouble.Funny how there steering boxes on their trucks dont have 1/2 the problems.


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## DaveK (Jul 9, 2001)

> Gm's valve isnt set with the correct bias


 That statement seems a little odd, since I am sure the brakes worked fine when new.


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## John DiMartino (Jan 22, 2000)

If it was as easy as buying a new 60 dollar Gm proportioning valve dont you think this post would have been put to rest long ago,and no not all thses things stopped good from the factory,my brother in laws 91 SBlazer 2 dr,never stopped good,not even when new.The back brakes were like new at 150K,fronts went bad every 15-25K.


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## plowking35 (Dec 21, 1999)

Like Gm never had problems from the factory.
Dave the only odd thing about this advise is that you never have anything usefull to contribute, but sure are quick to slam anyone elses thoughts and ideas. 
Like was mentioned long ago, an adjustable valve is the trick, but why spend the money when a simple fix will do. KISS


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## DaveK (Jul 9, 2001)

John, there are two different problems being discussed here. One is Murray's brakes (spongy/low pedal). The other is Alan's brakes (rears not applying). So yes, in Alan's case, a new proportioning valve seems like the solution. 
As far as this thread being "put to rest long ago", Murray brakes have a different problem. And as long as Murray keeps this conversation alive, I will participate.

Plowking35, in reference to this:


> Dave the only odd thing about this advise is that you never have anything usefull to contribute, but sure are quick to slam anyone elses thoughts and ideas.


First of all, saying that I never contribute anything useful is just your opinion. And your opinion means less to me than most others opinions here. I come to Plowsite because I enjoy it. You are here to sell your product. I'm curious, why don't you have an advertisement on Plowsite? Everyone else that is selling products through the use of Plowsite has one.

Secondly, I don't "slam" anyones thoughts and ideas. If anyone slams good ideas, its you. Should I link to the many posts you have made concerning plow wings, or Blizzard plows, or any number of other good ideas? In your mind, the only good idea in this industry is urethane edges. Sure, urethane edges are a great product, but they aren't the only great product.

As always, it takes a comment like yours to get this type of reply from me.

BTW, what were the results of your airline pressure test once you performed it correctly? Just kidding, I already know the answer.


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## Murray (Dec 17, 2001)

More input from Scotland; I talked to a friend of my dad's at the weekend, before retirement used to be the workshop manager of the Local Authority Depot, in charge of maintenance for about 100 vehicles, from refuse collection trucks, to small car-derived vans. Anyway, he recently had an accident repair on a 2-year old Ford Transit pick-up, about a 1-ton payload I think. The repair involved replacing the front left suspension, steering gear and hub, including new brake caliper and rotor ( I don't know what the driver hit with it, but I bet he had some explaining to do!!). Once the new parts were fitted, his guys bled and re-bled the system, but couldn't get a decent brake on the truck. Bill then phoned Ford U.K., who explained that in order to chase all the air from chambers within the ABS and the load sensing valve, a bleed pressure of about 45 to 50 psi was required! They did it, and it cured the problem on that truck. Now, I'm not suggesting a bleed pressure in that order is needed, but it is food for thought concerning this damned proportioning valve.
I'm waiting for parts at present to re-pipe the system,with a new valve too, because I think my problem is still related to Allan's in so much as I think it's the rears that are sapping pressure from the system. Think on this;
I already know my Blazer has had the wrong pipe installed from front to rear, one of a smaller diameter. I'll try and stick on a picture of the old and new lines. My guess is that the proportioning valve works to a certain extent on a set time scale, that is, on application of the brakes, bias is initially to the rear, then shifts to the front, and relieves the rear slightly, right? Well, what if there isn't enough time allowed for the right amount of fluid to get to the rear wheel cylinders, due to the smaller line size, or some restriction in said line, then as the bias switches to the front, there isn't enough volume of fluid at the rears to give any brakes to speak of. This is the same every time the pedal is pressed, as the spring return action of the shoes pushes the fluid out of the wheel cylinders back to the master, so it never gets better. It's all pie in the sky without the means to replace the line, so it has to remain a theory for now.
I did a while ago disconnect the rear line from the master altogether, and fit a blank as supplied with the re-con one. I got as far as the end of the drive way and turned back, the brakes were no better. What I didn't realise at the time was it was more of note that they were not any worse either!! Like I say, it's all in the air 'til I get some parts on there.


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## DaveK (Jul 9, 2001)

The proportioning valve works based on PSI rather than time delay as you suggested. As the brakes are applied, fluid flows to the rears initially, then when a predetermined PSI is reached in the rear line, fluid flows to the front as well. A smaller diameter line to the rear will not effect the PSI at either the proportioning valve, or at the rear wheel cylinders. The fluid will just have to flow a little faster to get there. As pressure then builds in both the front and rear lines, the valve regulates the bias.

And a bad proprtioning valve won't give you a low pedal.


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## Murray (Dec 17, 2001)

Is it possible that the smaller volume line is causing this psi build-up artificially early, closing the valve off before the rear brakes are fully engaged? There is a big difference in size, as you can see. The pedal on this car goes about half way down pretty easily, then feels spongey, or rubbery after that, all the way to about 1 1/2 inches from the carpet.


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## plowking35 (Dec 21, 1999)

Dont ever question my motives for posting on this or any other site. If I only wanted to sell my product then why would I even post on this subject? I asked my mechanic who is one of the most knowledgeable people I have ever met in the auto industry, and since he has fixed more than a few of these same exact problem, I trust his opinion and have rarely seem him be wrong. John D is also some one who has an extensive backround in auto repair, and I would also trust his judgement as well.
As for the air line pressure experiment, all I can say is this.
I use air tools every day in my work, and very simply put.
If I run out 1-50' hose and I am driving 3" nails into 2x material with the pressure set at 90 psi at the compressor, the gun will drive and set the nails fine, add another 100' of hose and the gun will not set the nails. I would need about 100 psi to do the same work.
That is real world experience, not therory.


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## DaveK (Jul 9, 2001)

Murray, no, the PSI cannot buildup till the fluid has moved the rear wheel cylinders and stops moving through the line. If the line were a very small diameter, it may slightly effect the timing of the rear brakes being applied, but the timing has little to do with the final actual bias or pressure ratio between the front and rear.

Dino, I trust John's judgement and respect his opinions. I was merely pointing out that there are two different brake problems in this discussion, and that I find it hard to believe that the proportioning valve from GM is set at an incorrect bias. I realize that cars do leave the factory with problems occasionally. But we aren't talking about a new model here.

As for the air line pressure experiment. We are dealing with closed hydraulic systems here. Your "real world experience" with an open air system has *absolutely* no relevance. If your airline was a closed system, then the PSI would be equal at both ends, even if it ran from Michigan to Connecticut. And that is not a theory. Your nail gun experiment has more to do with volume and airflow than PSI. It just so happens that more PSI at the regulator also gives you more CFM (cubic feet per minute).

I resent the fact that you often refer to real world experience in discussions with me, implying that I have no real world experience. The truth of the matter is that I have about 5 years more real world experience than you. But real world experience means nothing compared to real knowledge. Real world experience simply means that you have experienced something. Knowledge means that you have actually learned something based on either experience or education. The best knowledge is when it is based on both education and experience.

I am sure your mechanic is one of the most intelligent people you have met. However, when it comes brake sytems, I feel that if a part is broken or not functioning correctly, it should be replaced with a good part, not simply jury-rigged or modified to be acceptable. And your mechanic is setting himself up for huge liabilities if he has in fact tampered with the proportioning valve by cutting a spring. That does not seem wise in my opinion. And that opinion is based on education, not real world experience.


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## Chuck Smith (Dec 30, 1999)

I guess no one else noticed the copper tubing used on this brake system in the pic. Copper tubing on a brake system is a NO NO! It's too soft, and flexes much more than steel. Actually, you won't find copper lines on any vehicle. It is not DOT approved.

Just out of curiosity, doesn't the S-10 have seperate reservoirs for the front and rear brake fluid?

~Chuck


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## plowking35 (Dec 21, 1999)

In my discussions with Alan, himself and Murry are dealing with the same problems. Alan also has mentioned that he has replaced the valve many times and that didnt fix the problem. SO one must assume that something else is amiss. As John stated, many of these trucks if not all of them have left the factory with this problem. Many of the big auto makers problems have been fixed by back yard mechanics long before the auto maker ever found the problem. In fact the local dealers when my mechanic called to ask about TSB on this matter, mentioned that several s-series vehicles with bad rear brakes were sold as scrap because they couldnt get more rear braking. CT has a skid pad test that requires all 4 wheels to lock before passing. So GM doesnt have a fix for this either.
Yes a new adjustable valve is the perfect solution, however the simple fix can work. KISS
I mentioned that my mechanic is one of the most knowledgeable people in the auto industry, but you dave are by far the smartest person I have ever met. You must be since you seem to know everything.
I also never mentioned that you didnt have real world experience, but now that YOU bring it up, you may be onto something. Alot of things look real good on paper and on the puter screen, but a whole different ball game when put into practice. 
And I have yet to see you offer Murray or Alan an idea of how to fix this problem. At least I ahve done that much.
At any rate, the idea that I passed along is an easy and rather quick one to try. One could start with 1/2 a coil removed, reinstall the spring and see what happens. If it actually worksand you are not comforstable with a cut spring, at least they have direction to go in. If not, then a 2.00 spring from GM puts them back to stock, and no gets hurt.
Worse case scenario, they would have to much rear bias, and they rear would lock up. Since they need to do a gravel drive skid pad test, no harm would be done. I dont think anyone is advocating modifying the braking system to point of being dangerous, quite the opposite, the modification would make the system safer.
I dont know why you make such a big deal about this idea, except that you didnt come up with it. Come to think of it, unless its your idea, your not to fond of anyone elses.


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## thelawnguy (May 20, 2001)

The brake bias on these trucks is set very low in the rear from the factory, due to the fact that they are primarily small cars with big trunks. For the occasional golf bag in the bed the bias is fine; for anything heavier then a picnic basket, modifications seem in order.

I said it before, on my Dodge I replaced the original 15/16 dia rear wheel cylinders with 1 1/16 dia wheel cylinders and it made a world of difference for all of $25. Maybe a scan of the parts counter catalog will help you find a larger wheel cylinder which will give you more pressure on the rear shoes. My guess is that a cylinder from a Caprice/Roadmaster/Brougham would be the same, and they come in various diameters depending on the application.


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## Alan (Mar 2, 2000)

> _Originally posted by Chuck Smith _
> *I guess no one else noticed the copper tubing used on this brake system in the pic. Copper tubing on a brake system is a NO NO! It's too soft, and flexes much more than steel. Actually, you won't find copper lines on any vehicle. It is not DOT approved.
> 
> Just out of curiosity, doesn't the S-10 have seperate reservoirs for the front and rear brake fluid?
> ...


Chuck,

The copper stuff is apparently the British standard for brakeline replacement tubing. It is NOT the copper we would use here for fuel lines, but an alloy of several metals and is rated for some pretty extreme pressures. If you ask for brake line tubing "over there", this is what you get, the same as we get steel line here. The "copper" line is not the issue.


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## Alan (Mar 2, 2000)

> _Originally posted by plowking35 _
> *In fact the local dealers when my mechanic called to ask about TSB on this matter, mentioned that several s-series vehicles with bad rear brakes were sold as scrap because they couldnt get more rear braking. CT has a skid pad test that requires all 4 wheels to lock before passing. So GM doesnt have a fix for this either.
> Yes a new adjustable valve is the perfect solution, however the simple fix can work. KISS
> *


Dino, luckily VT doesn't have a skid pad test for brakes. If they did I know where there are three S models that would fail. And Murray is fighting with his brakes because his S won't pass the inspection in Scotland. I had grand plans to get into the worst one of my three, but haven't dared rip into it for fear of making it worse and having it down should we get snow.

I think my course of action will be to pressure bleed the system first and see if there is any improvement from that. Second step will probably be to go with an adjustable valve. It's not that I don't "trust" the spring clip but it's a pain to bleed things several times to get the spring right. Adjustable valve is $50 plus shipping and would give me the option of playing with pressure bias to see just what it takes to get things to work the best.


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## Murray (Dec 17, 2001)

Alan, thanks for your support on the brake line issue here. As I said before, the copper-nickel alloy used in the U.K., is common practice, and although more maleable than a steel line, is well up to the job, and capable of working pressures more usually found in hydraulic systems in general, not the pressures of automotive brake systems. This is what everyone uses here, dealers included!! I don't understand why they don't put it on from new, then we wouldn't be replacing the damned things! Maybe it's because it is of a higher spec than required, and of a more expensive material, therefore the cost per vehicle is prohibitive.
It does worry me though, that you have dealers over there who would rather admit defeat and I quote;

"In fact the local dealers when my mechanic called to ask about TSB on this matter, mentioned that several s-series vehicles with bad rear brakes were sold as scrap because they couldnt get more rear braking. CT has a skid pad test that requires all 4 wheels to lock before passing. So GM doesnt have a fix for this either." 

That DOES worry me. I only hope I haven't bought into a vehicle, made by the biggest vehicle manufacturer on the planet, that is impossible to get a working and safe brake on! 
I would find that prospect hard to swallow.
Further, I cannot buy into the possibility that a working brake system isn't acheivable without after-market or race-type equipment being fitted;
" Yes a new adjustable valve is the perfect solution "
Surely the proportioning valve as fitted and specified by Chevrolet is capable of providing the correct bias for the brakes on this car? If not, I don't think Chevy would be buying from that supplier.
And why would the brake bias NOT be set at the factory? In this country, the car arrives at the dealership with the plastic to take off the seats, and the shipping wax to pressure wash off, and she's ready to go!! Surely the dealers there are not expected to first-off go clipping springs in valves, and second, pressure bleed a brake system on a brand new car?
I'm intrigued. I didn't realise things were so different on your side of the pond!
But seriously, if this is a manufacturing problem, then should I, or we, be mailing Chevy?
Your thoughts, please. 

--------------------------------------------------------------------------------


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## plowking35 (Dec 21, 1999)

Yes I do think that anyone with this problem should contact GM. They need to have a repair for this type of item. Murray I agree with all that you have said, but sometimes it takes backyard wrenching to fix what GM wont / cant.
Dino


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## DaveK (Jul 9, 2001)

> And I have yet to see you offer Murray or Alan an idea of how to fix this problem. At least I ahve done that much.


Dino, since you somehow came to the conclusion that I offered no possible solutions, perhaps you should re-read this thread.



> I mentioned that my mechanic is one of the most knowledgeable people in the auto industry, but you dave are by far the smartest person I have ever met. You must be since you seem to know everything. I also never mentioned that you didnt have real world experience, but now that YOU bring it up, you may be onto something. Alot of things look real good on paper and on the puter screen, but a whole different ball game when put into practice.


 Well thank you Dino. But I don't exactly know *everything.* And I didn't say that you have ever mentioned that I don't have real world experience; I said that you implied that. I do have relevant knowledge in brake systems. (I have actually worked as a mechanic certified in brake and braking systems) You on the other hand, bring up totally irrelevant information about an airline on your nail gun. All I did was explain how and why it is irrelevant, so that others that read this thread won't get confused by comments that are essentially meaningless. If you take offense at that, I appoligize. 
-----



> I only hope I haven't bought into a vehicle, made by the biggest vehicle manufacturer on the planet, that is impossible to get a working and safe brake on! I would find that prospect hard to swallow. Further, I cannot buy into the possibility that a working brake system isn't acheivable without after-market or race-type equipment being fitted.


 I agree with that 100% Murray.

-----

Chuck, all cars since the 50s-60s? have seperate reservoirs and essentially seperate front and rear brakes. I think you already know that. So I am wondering why you posed that question.


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## CT18fireman (Nov 30, 2000)

DaveK 

I agree with you. Although sometimes a resevoir may appear single although it has a feed tube supplying two different parts of the master cylinder. This is how it is on both my Toyota pickup and 4runner. They actually only have one resevoir though.

I would agree that this problem should be able to be fixed without aftermarket parts. I cannot beleive that one of the most popular small trucks would have been made this way. Then again maybe that is why Japanese mini trucks are so popular. 

I would think that their must be a way to fix this problem without cutting and playing with internal parts of a valve. Further I always say with brakes you should replace parts not repair them. Do you really want to trust a spring that you had to cut inside a valve that controls the stopping of your vehicle? Not me.


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## John DiMartino (Jan 22, 2000)

I know the options dont sound good,but it looks like its cut the spring,which shouldnt be a big deal,or put an aftermarket valve in it.Id cut the spring,try a little at a time.It isnt any good now with no rear braking.Ct 18,I agree with you,i usually do not ever open,or rebuild wheel cyl,Master cyl,or or any brake parts/components anymore,just replace them for liability reasons alone,not to mention,its not worth your time to rebuild them anymore,but it looks like this one isnt going to get fixed any other way.My 84 S10 pickup had excellent brakes,the pedal was nice and high/firm,and the truck would lock up the rears first empty,which is how it should be.Some have the problem,others it seems do not.My 89 GMC,2500 has this problem,while my 91 stops great,weird.


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## DaveK (Jul 9, 2001)

I have a question for Murray and Alan. 

Do you both have the identical problem with your brakes? 

The way I understand it:
Murray has a low/spongy pedal with very poor braking as a result.

Alan has a "very similar" problem. "Front brakes work so-so at this point, rears are a joke." No mention of pedal travel or low/spongy pedal.

Part of the problem here is that there are attempts to diagnose two different trucks with problems that may or may not be related. 

So that you both won't describe the same symptoms using different descriptions, maybe it would help if we just have you answer a few questions with yes or no.

1. Does the pedal travel too far before applying brakes?
2. Is the pedal very spongy after resistance is felt?
3. Is the pedal slightly spongy after resistance is felt?
4. On gravel, will the front brakes lock-up?
5. Were the rotors recently re-surfaced?
6. Were the drums recently re-surfaced?
6. Is the firewall solid? (brake booster not moving when applying brakes)


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## TurfPlus (Dec 19, 2001)

Just a thought since I haven't followed the entire thread. Have you tried adjusting the brake booster rod or checked it to make sure its adjusted properly? I can walk you though it. Also are the rotors and drums with in specs?


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## DaveK (Jul 9, 2001)

TurfPlus, I mentioned the booster rod earlier.



> I just thought of another posibility. There is an adjusment (not totally sure on the S10) for the gap (or lack of) between the rod that applies pressure and the piston in the master cylinder. If it is adjusted to far, it wouldn't let the piston return fully to the normal state. If the gap is to large, the pedal would move quite a distance before beginning to apply the brakes. And remember, I do know that on some vehicles it is adjustable, but I am not 100% sure on the S10, so don't go breaking anything trying to adjust something that can't be adjusted.


Staley52 replied with


> I have rarely come across a push rod adjustment problem. The only time that I have adjusted them is when replaceing boosters, when replacing master cyinders I never adjust. The machining of the master cylinders are almost always identicle. pehaps if they put the incorrect master on the truck the push rod may be off but this is NOT fixed with adjustment it is fixed with the correct part.


Being that I was not 100% sure that it could be adjusted on the S10, I didn't bring it up again.


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## Murray (Dec 17, 2001)

Thank God, someone with a logical mind!! Can I borrow it? DaveK, thanks, the questionaire is a good idea. I have corresponded with Alan outside this thread, and I think we are both pretty much talking about the same thing. That is, very poor braking, especially at the back. Unfortunately, our s10's are about 3000 miles of ocean away from a mutual test drive! But to address your questions for my case;
1. Yes, pedal is travelling too far, almost all the way.
2. Yes. Brakes are very spongey after that.
3. No. not a little, a lot!!
4. Just locking the fronts, but not on pavement, even wet.
5. No.
6. Yes. The drums were milled out by the previous owner, but the parking brake would hold on a cliff, and the adjusters are only about one-third out to contact the shoes and drum.
6.(?) Yes, the firewall is solid, the only rust on mine seems to be the rocker panels and box sections underneath.
Hope this helps to picture the fault.


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## CT18fireman (Nov 30, 2000)

Will the parking break hold tight without being pulled out very far? In other words are the rear shoes close to the drum? I know this may seem trivial but better to cover simple things.


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## Murray (Dec 17, 2001)

Yes, the parking brake is very good, only needs about half the pedal to hold on quite a steep driveway. The adjusters were set as tight as would allow the drums back on.


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## DaveK (Jul 9, 2001)

After doing much thinking, I have came up with a few conclusions.

*1. Cutting the spring will not help with low pedal and/or poor braking.* Regardless of the timing of the rears being applied in relation to the fronts has nothing to do with the final pressure at the wheels. And regardless of the bias or ratio of braking power, you would still have a firm pedal. 
The proportioning valve limits the flow to the rear brakes *after* a certain pressure has been reached, and this split point can be anywhere from 200 to 500 psi. Above that, force in the rear lines is allowed to rise at only a portion of the maximum available. *The valve does absolutely nothing in normal, low-pressure stops.*

*2.* Just as in my second post in this thread says (even though Dino says I haven't offered any useful information), "Once you are confident that all the air is out of the system, which could be quite a bit with new calipers, master and wheel cylinders, everything points to the master cylinder." "The proportioning valve (really a combo valve) won't effect pedal travel. It warns you when you lose front or rear brakes through the brake warning light. It applies pressure to rear brakes slightly before the front. And it gives the rear brakes a lower percentage of breaking power than the front. None of which, if not working correctly, would give the symtoms you have now."

You guys that are sure that it has to do with the proprtioning valve, pay close attention to this paragraph. 
If the spring in the proportioning valve were too long/short or too strong/weak, there would still be a firm pedal AND either the front or rear brakes would be getting MORE pressure than usual, which would certainly give more than adequate brakes for that half of the system. The idea of giving more bias to the rears is ridiculous in the sense that you would be taking more of the total braking power AWAY from the front brakes, which are not very good on Murray's or Alan's vehicles as it is. And the majority of the braking power SHOULD be at the front wheels where most of the weight is when standing still let alone when the weight is transfered forward as when stopping. If anyone still feels that it is the proportioning valve, re-read the above paragraph until you fully understand it. This expanation is more in depth and gives a better "picture" than the one in the second post I made in this thread.

Now this is obvious, or shoud be. 
*The real problem is that the pressure needed at the calipers and wheel cylinders is not being achieved.* So let's attack this in depth.

The first cause could be air in the system. Both trucks have had new master cylinders installed. If not "bench bleed" there could be trapped air in the master cylinder. Both truck have had new lines installed. If there are loops or many ups and downs in the line, it can be hard to get all the air out without a good pressure bleed.

Now, if there is absolutely no air in the system, then the only other hydraulic posibility that would prevent the lack of needed pressure at the calipers and/or wheel cylinders, is an internal leak in the master cylinder. Just for the sake of mentioning it, if it were an internal leak in the proportioning valve, there would still be no loss of pressure in the total system, just an equalized pressure between the front and rear.

So here is my final "useful" advice. 
If you did not bench bleed the master cylinder, you can still do it after it is installed on the truck. However, you should raise the rear of the truck so that the master cylinder is sitting level. Then attach hoses from the output lines looped back up into the reservoir to below the fluid level. SLOWLY depress the brake pedal and release. Wait about 10 seconds and repeat. Continue this till there are no air bubbles.

Now, make sure there are no "high spots" in the new lines where air could "hide" and then pressure bleed the system. To be sure that you have gotten all the air out, allow for quite a bit of fluid to flow through the system (more at the rears of course).

After doing the master cylinder bleed and the system bleed, if the brakes are still poor. I would suspect an internal leak in the master cylinder, which isn't all that rare in a re-con.

Another possibility is the hoses or lines expanding and not allowing the pressure to build at the calipers and wheel cylinders. Although Murray and Alan seem confident that this is not the case. So, one other non hydraulic alternative is the push rod length. Which would be more of a problem if the booster was changed at some point in time. But can exist if physical stress has altered the gap or lack of (booster, firewall, pedal assembly, etc). Or if the master cylinder is not quite within specs. Another non hydraulic alternative is the pads/shoes being glazed over or the rotors/drums being glazed over. If the rotors and drums have been re-surfaced and new pads/shoes were installed, this is probably not a concern.

If anyone sees any flaws in my advice, feel free to post your reasoning. I have an open mind (unlike others).


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## CT18fireman (Nov 30, 2000)

Spongy pedal means air to me. I would think it would be air. This may require a LOT of bleeding to get all air out. Starting with the master cylinder and working throught the whole system. Only then do I think the culprit could be the master being bad. I think DaveK is on the right track. 

When I rebuit my Toyota and ran new lines to the rear it took quite a long time to get good pressure at the rear blakes. Make sure you have all the air out.


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## cj3859 (Aug 27, 2001)

so you have changed everything but the booster and proportioning valve, brilliant deduction would say change last two items(not simultaneously) rebleed and if that doesnt do it,you probably got hold of an expertly remaned peice of crap master cylinder.

ps for those out there who seem so much smarter than the rest of poh dum folk how come your wasting your time here helping us last time i checked advice is just that "ADVICE" you can use it or lose it. hope ya get it sused out dude


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## Murray (Dec 17, 2001)

Okay, a lot to take in there!

I agree,the problem IS that the pressure needed at the calipers and wheel cylinders is not being acheived, the debate is, where did it go!!
DaveK, I do not have your knowledge of this system, but surely there could still be a restriction in the proportioning valve, preventing not just operation of the rears, but full pressure to the fronts?
Also, it IS possible I didn't do a perfect job of bench bleeding this master, so I will try that.
If the master has an internal leak, what are the symptoms? There is no evidence of fluid escaping anywhere, and if the two valves were "bleeding" into one another, would it matter? I don't understand the workings of an American master cylinder, the way they puke fluid back into the reservoir is beyond my comprehension! When bleeding a Europian system, the lid can be left off, and you can pump away to your heart's content, without a geyser of brake fluid all over the underside of your hood! I learned that with my first American car!!
My gut feeling is that, other than a few restrictions in the system, thee is still air in there, that is how it feels at the pedal. Trouble is, I'll be damned if I can bleed it out! I haven't tried jacking the rear end to level the master though, so I will try that first chance I get.
There does seem to be an underlying problem here with this vehicle though, and I've been holding out for somebody to come up with a miracle cure.
Can someone answer the question of whether the system will operate without a proportioning valve? At this stage, I don't care if the rears lock up on me!
Sorry, DaveK, but I did see a flaw in that theory. If the master cylinder houses two separate systems, then no amount of adjustment or alteration of the rear braking force will detract from the force available to the fronts. The two systems, as I see it, are operating independantly, by means of the booster rod pushing on the double valve inside the master, they are not sharing a pressure between them. Sorry!


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## mowahman (May 6, 2001)

try this: open the front right bleeder, just a crack, fill fluid reservoir, then proceed to bleed rear brakes starting with the right rear until you get good solid fluid streams. Close off RR bleeder. Go over to Left Rear and bleed until you get good solid fluid streams. While doing the rears, check the fluid level often. After bleeding the rears, tighten up the front right bleeder, check fluid, try pedal. If necessary, you may have to bleed the fornts, starting with the Front Right then onto the Left. What happens sometimes, like when a brake line fails, the portioning valve will effectively "close off" the supply to the failed line. In doing the above, you have the portioning valve "think" that the fronts are losing fluid so the slide will close off the front, thus opening the port to the rear supply. This is the way the dealer did it to mine, charged me dearly only ONCE, as I was present and taking notes in this class !! Once done properly, with all the air out of the system, your brakes should work fine. This has happened to me more than I like, owning a 1974 Chevy K10 up here in "Rust Country". good luck. i have also done some work on the adjustable valve as mentioned in the thread, Wilwood brand on a ProStock race car that I am crewchief with. You can get all front to all rear brake, or adjust to somewhere inbetween (adjustment is usually done by the nut behind the wheel, I don't get in the thing.......just wind up fixin it !!!). As to running without the portioning valve, I myself wouldn't do that for the mere reason and none other than "just because". It's on there for some reason so taking it off or bypassing it may cause ??????????? I don't know.


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## DaveK (Jul 9, 2001)

> I did see a flaw in that theory. If the master cylinder houses two separate systems, then no amount of adjustment or alteration of the rear braking force will detract from the force available to the fronts. The two systems, as I see it, are operating independantly, by means of the booster rod pushing on the double valve inside the master, they are not sharing a pressure between them.


Yes Murray, they are seperate from each other. But the proprtioning valve divides 100% of available pressure. If the front gets 70% and the rear gets 30%, then by using an adjustable (or modified) proportioning valve and giving the rears 40%, the front is reduced to 60%. If there were no proportioning valve, then "no amount of adjustment or alteration of the rear braking force will detract from the force available to the fronts" would be true.

It would depend on what type of an internal leak in the master as to what the symptoms would be. It could be low pressure to one half of the system or to both.



> but surely there could still be a restriction in the proportioning valve, preventing not just operation of the rears, but full pressure to the fronts


 I really don't think there is a restriction. More likely is that there is still air in the system (anywhere from the master to the end) that is causing the excessive pedal travel and well as being spongy and "preventing not just operation of the rears, but full pressure to the fronts".

BTW Murray, I replied to your PM as well.


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## plowjockey (Dec 3, 2000)

I don't know if I gave this reply already or not, the post is so long at this point. 
When I used to build Harley's sometimes the systems would not want to bleed up to pressure. When all else failed I would drain the system and then fill from the bleeders thereby pushing all of the air out the master cylinder and having no bubbles. I don't really know if this would help in this situation.

Bruce


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## thelawnguy (May 20, 2001)

When you changed the rear wheel cylinders, did you make sure the new one sat nice and flush against the backing plate? Did you make sure the cylinder was tight, and didnt have the least bit of side to side movement? Those @#$%^ing GM cylinders with the round retainer clip will cause all sorts of problems. They are notorious for loosening up and rocking in their mounting hole and roundingit out. If there is any play at all it will magnify itself through the system. Whenever I change the wheel cylinders of this type I also install the repair kit sold specifically for these, consists of a heavy bracket and two self-tapping 1/4 inch bolts, you install the cylinder best you can, mark the retainer bolts drill two 15/64 holes through the backing plate and mounting flange and bolt it down.

Brought the pedal on my Bonneville from near floor level to high and hard lol.


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## RALMETER (Jan 31, 2002)

Where is the proportioning valve located? I have a 84 Silverado with a valve leaking on the rear axle, the break line goes in and comes back out, there is a round rubber disk on the side of this valve which is leaking. 
Thanks in advance for any help

Ron


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## plowking35 (Dec 21, 1999)

Ron what you have is totally different than the s-10 series trucks.
Your valve is located on the most forward crossmember under the front of the engine. The valve in the rear is a weight sensitive unit, it will allow more rear braking as the truck lowers due to weight in the bed.
Dino


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## chevy (Jan 21, 2002)

Just my two cents, but I had a problem with my c-30 with crummy brakes for about a year. Tried every thing, then I bought a Clitons total car care book. After reading the brake section, I found out that the way to bleed those brakes was quite odd to me. Open the bleeder(farest away) depress the brake pedal, hold down, tighen the bleeder, and repeat the procedure until clean fluid comes out. Do this for the rest of the brakes and see what happens. Sounds a liitle unorthadax, but it worked for me really good. I thought that pressure bleeding was the best way. I was wrong in this case. For nothing give it a try got nothing to lose.


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## Murray (Dec 17, 2001)

Hi, welcome to the biggest thread on the site!
Looks like the Brits are exporting to the U.S. after all!! That is the common method of bleeding brakes over here, and normally involves falling out with your wife, as she presses when she shouldn't, or gets bored and wants to stop half way through. The concept of pressure bleeding is new to me, and I have cobbled together a bleeder from odd bits, including a pressure vessel from a friend's set. U.K. masters have screw-on caps, like your clutch slaves , which makes it easy to fit a cap with a pressure line. These clip-on lids don't make things easy, and I made up a frame of screwed rod and flat bar, with a rubber end to fit over the outlet from the reservoir.
Short answer is, thanks, but tried both methods of bleeding, and still mushy brakes. I have stuff coming from the U.S. now to re-pipe the car, new proportioning valve, new flexy lines, mentioned way back, the works. I will jack the car up to level the master, and bleed that too.
Any new ideas are gratefully received though!


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## Murray (Dec 17, 2001)

Here's a picture of my home made bleeder.


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## DarrellD (Nov 4, 2007)

*DarrellD*

New guy here with a very similar problem.
I have a 1979 Chevrolet C-10, 6 cyl, 4-spd. that I bought brand new.
Problem:
When I step on the brakes, they will stop the vehicle just fine, however,
the pedal will go all the way to the floor. The wheels will lock up and the truck will skid,
and this happens when the pedal is halfway to the floor, but the pedal will continue
to travel to the floor.
I have replaced the rotors, drums, rear wheel cylinders, front calipers (twice), all brakes,
vac booster (twice), master cylinder (4 times). 
After all of this, the problem has not changed.
On the master cylinder, when I plug the front brake line outlet at the master cylinder and the 
rear brake line outlet, the pedal is hard and firm with zero fade.
When I connect the rear brake line and leave the front plugged, the pedal is hard and firm with zero fade, just normal travel as the rear brakes are applied.
The parking brake is rock solid with very little travel in the parking brake pedal when stepped on.
When I plug the rear brake line at the master cylinder and connect the front brake line,
the pedal fades to the floor.
I have zero loss of brake fluid and zero air in the lines.
There are only two things yet to replace.
The proportioning valve, and the front brake hoses. The section of hose that runs from the 
frame to each front caliper is rubber.
My conclusion: Either the proportioning valve is faulty, or the rubber section of front brake hoses are swelling under pressure (which I have not observed yet), or maybe I need to purchase a fifth brand new master cylinder. You guys sound like experts to me, any
suggestions?


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## DarrellD (Nov 4, 2007)

After reading DaveK's response earlier about the proportioning valve, It makes sense
that it's not the culprit. So I will examine the front brake rubber hoses. They are the original hoses (28 years old) with over a million miles on them. I'll post my findings and anxiously await any response. Thanks


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## wild bill (Feb 10, 2007)

*woah !*

just a thought but how thin are the brake drums and rotor's you loose a lot of brake travel on thin drums ,you can only turn them so much . and nobody arches shoe's to fit the drum's any more the brake fluid is a valid thing to look at some time's you have to flush the system out if you have moisture and contaminant's in it .


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## DarrellD (Nov 4, 2007)

Thanks for the response, and I forgot to mention,
I did replace the rotors and drums with new ones.
I have inspected the front hoses under pressure, and there is
no swelling.
However, while watching the booster and master cylinder while the
pedal is depressed, I noticed forward to back movement of the booster and master cylinder.
I cant tell yet if the firewall is moving, or if it's more of an expansion of the booster itself.
The firewall does not appear to be moving, but the travel at the master cylinder is about
1/2 an inch.I


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