# Torsion bars breaking?



## mkwl (Jan 21, 2005)

Has anyone ever heard of (or experienced) cranked torsion bars snapping under load (i.e. plow) before? I wan thinking about it today and wanted to see what your experiences ahd been.

Matt


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## wild bill (Feb 10, 2007)

*give me a break*

i have never seen one break from normal loading (ie) plow ,i saw a f150 break both one right after the other ,just pulling out of the drive with no plow .


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## millsaps118 (Aug 13, 2006)

I never broke one but I know they will snap like a tooth pick if you crank the T-bars up and hit a pot hole or something to that effect, ie. sudden/brunt impact or jolt to the front susp. This can happen with or w/o a load on the front.

Exact reason I never turn my T-bars any more than 8 turns-in.


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## lehmand1 (Dec 17, 2007)

I don't think cranking a torsion bar would make any difference wether on not it will break. I have never heard of it happening.

Cranking the torsion bar doesn't put any more stress on it. The only thing that it stresses are the driveline angles of the cv shafts. You are just in a sense re-indexing the torsion bar, it still has the same spring rate and can carry the same load. It doesn't make it any stiffer. If your plow makes your front end drop 1", it will drop that same amount no matter where your torsion bars are set at.

Some people think that cranking them up makes there truck ride rougher, this is not because it is stiffer. If you crank them all the way up, your suspension is close to reaching its maximum downward travel (shocks, a-arms, etc) then when you go over a bump or pot-hole, your suspension can't travel down far enough to compensate.


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## millsaps118 (Aug 13, 2006)

lehmand1;495019 said:


> I don't think cranking a torsion bar would make any difference wether on not it will break. I have never heard of it happening.
> 
> Cranking the torsion bar doesn't put any more stress on it. The only thing that it stresses are the driveline angles of the cv shafts. You are just in a sense re-indexing the torsion bar, it still has the same spring rate and can carry the same load. It doesn't make it any stiffer. If your plow makes your front end drop 1", it will drop that same amount no matter where your torsion bars are set at.
> 
> Some people think that cranking them up makes there truck ride rougher, this is not because it is stiffer. If you crank them all the way up, your suspension is close to reaching its maximum downward travel (shocks, a-arms, etc) then when you go over a bump or pot-hole, your suspension can't travel down far enough to compensate.


I don't know where you get your Torsion bar info from but they WILL SNAP. "TORSION" is derived from the word "TORQ", so in relation to a torsion bar, a twisting or turning effect (torq) is being exerted on that log skinny piece of steel that connects from your lower control arm (susp. component) to a cross member . When your IFS moves up and down, that torsion bar twists. 
When you turn your T-bar bolt in (raising up) you are twisting/turning the T-bar through the "key" applying load to it causing the front susp to ride higher than stock. When you apply a load to something no matter what it is, it's just a matter of time before it fails.
The tension on a torsion bar can only take so much and steel can only be twisted so far before it breaks.

Lehmand...you be the ginnie pig and turn your T-bars in as far as they will go and drive around for a while over ruff pavement, post back and update us all when they snap.
BTW turning the bars does make the truck ride stiffer and ride ruffer....., why do you think you feel it when its done????????


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## lehmand1 (Dec 17, 2007)

First of all, I did not say that they will not snap. I said that they won't snap as a direct result from cranking them up. When you crank up a torsion bar, you are not putting any more twist into it than it had before. The amount you crank on the key is the amount it raises your lower control arm. The only way cranking it up would put more twist into the bar would be if your lower a-arm didn't move at all. But that wouldn't give you any lift would it.

As to a truck not riding rougher I think I explained it pretty well in my post. It does feel rougher but it is not stiffer. If you hang an 800# plow on your truck and it drops the nose 2 inches you would expect if cranking them up made it stiffer it would then only drop 1 inch.
But this is not the case, because the "spring rate" is the same. GM sets the suspension up from the factory for it to be able to travel a fair amount in both directions(bound and rebound). When you turn your bars up you are taking away a lot of downward travel and adding it to the amount of upward travel. Then when you go over a pothole or bump, your suspension and wheel do not travel far enough downward to take up the jolt, thus making the truck ride rougher because your suspension cant travel any farther.

On a final note, I bought my truck new, I have 78,000miles on it, hauled countless loads of wood across rough fields with it, I live on a gravel road, and have plowed with this truck for the last 3 years, and I have had the torsion bars cranked all the way up since the first year I owned it. So I guess I already am the ginnie pig.


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## NBI Lawn (Oct 15, 2007)

millsaps118;495052 said:


> I don't know where you get your Torsion bar info from but they WILL SNAP. "TORSION" is derived from the word "TORQ", so in relation to a torsion bar, a twisting or turning effect (torq) is being exerted on that log skinny piece of steel that connects from your lower control arm (susp. component) to a cross member . When your IFS moves up and down, that torsion bar twists.
> When you turn your T-bar bolt in (raising up) you are twisting/turning the T-bar through the "key" applying load to it causing the front susp to ride higher than stock. When you apply a load to something no matter what it is, it's just a matter of time before it fails.
> The tension on a torsion bar can only take so much and steel can only be twisted so far before it breaks.
> 
> ...


X2, I cant understand why people dont get this. Cranking your T-bars is not a good idea ! Sure if you do like one turn you would probably be fine but dont try to get a 3" lift out of it. Cranking them does cause added stress. When you turn the key you are just twisting the bar more, they can only twist so far before they fail. 
I have seen them break before. I dont think they will crack, with the stress on them they will probably just break right away.


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## lehmand1 (Dec 17, 2007)

But you are not twisting the bar more. The only way to twist the bar more is to add more weight to the front end. And then you would be twisting the bar regardless of wether you crank the key up or not. All cranking the key does is re-index the bar, it does not twist the bar or put anymore stress on it. 

The biggest thing that cranking them stresses is the CV shaft angles and it can sometimes over extend the shock absorbers.


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## ticki2 (Jan 10, 2006)

NBI Lawn;495575 said:


> X2, I cant understand why people dont get this. Cranking your T-bars is not a good idea ! Sure if you do like one turn you would probably be fine but dont try to get a 3" lift out of it. Cranking them does cause added stress. When you turn the key you are just twisting the bar more, they can only twist so far before they fail.
> I have seen them break before. I dont think they will crack, with the stress on them they will probably just break right away.


When you adjust the rear of the torsion bar you are not twisting the bar , you are turning it , thats why it raises the lower control arm. If you add weight (plow) it will twist the bar ( more torque) . The harsher ride comes from the other front end compnents not being in proper position relative to each other. The only way to stiffen the suspension is to change the bar rating , or add a component. Then again, maybe I don't get it.


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## NBI Lawn (Oct 15, 2007)

ticki2;495606 said:


> When you adjust the rear of the torsion bar you are not twisting the bar , you are turning it , thats why it raises the lower control arm. If you add weight (plow) it will twist the bar ( more torque) . The harsher ride comes from the other front end compnents not being in proper position relative to each other. The only way to stiffen the suspension is to change the bar rating , or add a component. Then again, maybe I don't get it.


Incorrect, so why is it that when you lift it properly with a lift key it doesnt ride like crap? You are changing the angle of the front end components.
http://images.google.com/imgres?img...v=/images?q=gm+lift+keys&gbv=2&svnum=10&hl=en

Every turn of the key twist the bar more. So lets just say as you tighten it the rear part of the bar closest to the key rotates 1/2 turn, the front has only turned 1/4 turn, the t-bar is twisting and under more stress in an attemt to raise the front more.


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## ticki2 (Jan 10, 2006)

NBI Lawn;495615 said:


> Incorrect, so why is it that when you lift it properly with a lift key it doesnt ride like crap? You are changing the angle of the front end components.
> 
> Every turn of the key twist the bar more. So lets just say as you tighten it the rear part of the bar closest to the key rotates 1/2 turn, the front has only turned 1/4 turn, the t-bar is twisting and under more stress in an attemt to raise the front more.


If by lift key you mean the green keys it will ride like crap if you don't some other things , like shocks and bump stops. If you go aftermarket lift , it will have a new control arm plus shocks.

If you rotate the rear a 1/2 turn , the front will rotate a 1/2 turn . The front weight is the same no matter what height.


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## lehmand1 (Dec 17, 2007)

The link to those keys didn't say anything about not "riding like crap". Them keys do exactally the same thing that the adjuster bolt does. It re indexes the rear of the torsion bars. The only difference is "without the chance of stripping out the stock adjusting bolt."
They lift the vehichle at the same point, in the same way(by re-indexing the rear of the bar).

They even admit that the angles in the front end will be changed, but they say "PLC believes that the small increase in driveline angle is not enough to cause concern among 4wd owners, however a slight increase in CV boot wear is possible and should be watched.

There is absolutly no difference in this lift and a "crank them up" lift as far as your front end and ride quality is concerned. The only difference is the method as to how they re-index the torsion bar.


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## lehmand1 (Dec 17, 2007)

ticki2- Im glad someone out there agrees with me on this on.
I was begining to think I was fighting a loosing battle.

Well off to go cut firewood for the daywesport


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## NBI Lawn (Oct 15, 2007)

ticki2;495620 said:


> If by lift key you mean the green keys it will ride like crap if you don't some other things , like shocks and bump stops. If you go aftermarket lift , it will have a new control arm plus shocks.
> 
> If you rotate the rear a 1/2 turn , the front will rotate a 1/2 turn . The front weight is the same no matter what height.


They call them keys, did you follow the link? Real lift kits do not come with new control arms, not for a 4x4 anyway. They lower the cross member for the control arms. Some come with taller spindles.

They do not turn equally. As the stress is increased one side will rotate more.


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## NBI Lawn (Oct 15, 2007)

lehmand1;495629 said:


> ticki2- Im glad someone out there agrees with me on this on.
> I was begining to think I was fighting a loosing battle.
> 
> Well off to go cut firewood for the daywesport


Unfortunatly you guys are wrong. The reason the ride is stiffer is because the t-bar cannot twist much more.

Lift keys are made so the t bars are not twisted more than stock while at the same time allowing the the position to be in a lower spot. Make sense? Here is a picture that may help.

I dont care what you do but you are twisting the t-bars more than they should be especially after you put a load on them, ie plow.


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## JD Dave (Mar 20, 2007)

NBI Lawn;495697 said:


> They call them keys, did you follow the link? Real lift kits do not come with new control arms, not for a 4x4 anyway. They lower the cross member for the control arms. Some come with taller spindles.


I'm not exactly sure what your talking about. When you buy a Cognito Leveling kit it does come with new UCA's. They move the bump stop so when your bars are cranked, your truck isn't resting on the stops. The kit comes with shock extenders also but I would recommend longer shocks. Another thing is on most 2001 and up 3/4 and 1 ton pickups your stock keys are fine. There is nothing wrong with running your tb adjusting bolt all the way in if that's the height you want. I wouldn't run fully cranked with my blade on the truck though but some guys do. I've levelled alot of trucks over the years and I've never needed green keys. A spindle lift is for a 2wd truck if I'm not mistaken and I'm running the new UCA's on the 4" Cognito on my new GMC 4x4.

On edit. I just read your link and I guess some 4x4 lifts are knuckle lifts. I would like B and B to give his thoughts on this but I see no use to putting the keys in unless you can't get enough height out of the old ones. I have never stripped my t-bar bolts and my truck did ride like crap untill I put the shock extenders in. I'm just debating this, not trying to start a fight. BTW I've never even heard of a t bar snapping.


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## JD Dave (Mar 20, 2007)

lehmand1;495627 said:


> The link to those keys didn't say anything about not "riding like crap". Them keys do exactally the same thing that the adjuster bolt does. It re indexes the rear of the torsion bars. The only difference is "without the chance of stripping out the stock adjusting bolt."
> They lift the vehichle at the same point, in the same way(by re-indexing the rear of the bar).
> 
> They even admit that the angles in the front end will be changed, but they say "PLC believes that the small increase in driveline angle is not enough to cause concern among 4wd owners, however a slight increase in CV boot wear is possible and should be watched.
> ...


I should have just agreed with you, instead of posting. These shops selling keys lifts like to really stretch the truth to get you to buy something you don't need. JMO


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## millsaps118 (Aug 13, 2006)

lehmand1;495600 said:


> But you are not twisting the bar more. The only way to twist the bar more is to add more weight to the front end. And then you would be twisting the bar regardless of wether you crank the key up or not. All cranking the key does is re-index the bar, it does not twist the bar or put anymore stress on it.
> 
> The biggest thing that cranking them stresses is the CV shaft angles and it can sometimes over extend the shock absorbers.


Little article from Truckin' mag. 
http://www.truckinweb.com/tech/susp...pension_handling_performance/torsion_bar.html

Who ever wrote this must have miss-informed A LOT of people then......... :waving:

Here's another link to a thread on PS back in JAN '08. go down to post 15 and check the link out. http://www.plowsite.com/showthread.php?p=487781


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## NBI Lawn (Oct 15, 2007)

JD Dave;495708 said:


> I'm not exactly sure what your talking about. When you buy a Cognito Leveling kit it does come with new UCA's. They move the bump stop so when your bars are cranked, your truck isn't resting on the stops.


I guess I dont know but if you raised the truck wouldnt the control arm be further away from the bump stop, not resting on it?

Why do they even make a leveling kit if all you have to do is crank the piss out of you t bars


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## saabman (Sep 20, 2007)

When you crank the bar, it moves the lower control arm down (raising the truck). This moves it away from the bump stop. When the jacked suspension compresses, the lower control arm has more distance to travel before hitting the OEM bump stop. As such, it sweeps a greater angular distance, it will twist the TBAR more than it could of when the lower arm sat closer to the bump stop. This is why new bump stops are offered on some lift kits. They make sure the suspension does not "over travel". If you the suspension twists the bar to much, it will break.

This is similar to putting lift blocks on a leaf springs and not lengthening the bump stops. In this case the spring can "invert"


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## millsaps118 (Aug 13, 2006)

NBI Lawn;495948 said:


> I guess I dont know but if you raised the truck wouldnt the control arm be further away from the bump stop, not resting on it?


NBI...just the opposite of what your thinking, when you raise the front via t-bars it brings the LCA (lower control arm) closer to the bump stop. You increase travel height and lose downward travel. That's why you get a ruffer ride, the LCA is closer to the stop impacting it much sooner than if it were set at stock height.


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## ticki2 (Jan 10, 2006)

millsaps118;495912 said:


> Little article from Truckin' mag.
> http://www.truckinweb.com/tech/susp...pension_handling_performance/torsion_bar.html
> 
> Who ever wrote this must have miss-informed A LOT of people then......... :waving:
> ...


The Truckin' article is not miss-leading , it says that as the suspension travels ( while driving) the twisting of the torsion bars is adding stress to the bar , and over time it will fatige and fail . It says nothing about adding stress with the initial height adjustment. When going down the road one end of the bar is fixed so any movement in the other end will add or subtract torque. When adjusting the bars both end are able to move so no torque is being added or subtracted. The initial torque on the bars comes from the weight of the front end.


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## JD Dave (Mar 20, 2007)

millsaps118;495962 said:


> NBI...just the opposite of what your thinking, when you raise the front via t-bars it brings the LCA (lower control arm) closer to the bump stop. You increase travel height and lose downward travel. That's why you get a ruffer ride, the LCA is closer to the stop impacting it much sooner than if it were set at stock height.


Actually it's the upper contol arm where the steel stops are. The steel stops limit up travel and the rubber stops limit down travel. Here's a good right up about the Cognito kit.http://norcaltruck.com/cognito-2-3.html


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## saabman (Sep 20, 2007)

Perhaps we need to qualify the model of truck. But on a classic K1500 the factory bump stop limits upward travel (to keep your suspension from bottoming out on compression). As you can see in this picture of my Timbren install, the Timbren replaces the bump stop and acts as a helper spring during compression.










Cranking the TBAR will move the LCA down (away from the bump stop, and effectively raising the front end). My earlier point is that the greater distance from the bump stop, in the extreme, can cause the TBAR to over twist and break on full compression


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## B&B (Nov 4, 2006)

First of all I want to clarify for reference, "cranking" and "turning" the TB's are two completely different things in reference to making an adjustment. When a person refers to "cranking" the TB's, this is saying that they're adjusting them as far as they would physically go. Either by running the adj bolt in until it's out of threads, or if the bars are stiff enough for the weight capacity, raising the truck with the adj bolt until the UCA is pushing directly on the bump stop (thus eliminating all droop travel, resulting in a rougher ride). "Turning" is making a reasonable adjustment to gain a proper height, or to help LEVEL up the truck. Not to raise it beyond it's intended range of suspension travel. If you've ever noticed in any of my posts, I never say "crank" when referring to a TB adjustment, I always say "turn". They are two completely different things.

Now to adding "pre load" to the bar with the adjuster bolts or replacement keys..

This is a direct quote out the the Truckin article that millsaps posted and describes why turning the adjuster bolt DOES NOT PHYSICALLY "TWIST" THE BAR AT STATIC RIDE HEIGHT (and saved me from having to type it all LOL)


> Another con is as you increase the ride height by adjusting your keys, the ride gets worse. Now it's a common misconception that there is more of a load on the bar and this is the cause. That is impossible since the LCA moves as well, so there is no more torsion on the bar than before, the spring rate does not actually change like many believe. The twisting action does not add pre-load or change the tension on the bar directly, so cranking your bars is just like adding a block in the rear or a coil spacer. It is simply changing the position of the spring. Just to clear things up, pre-load is the amount by which the torsion bar can't return to its original (unloaded) position due to be installed in the truck. The reason for the bad ride quality is instead a combination of things. First of all, when you adjust the height up, the angle between your LCA and the ground is increased which effectively does reduce your pre-load by reducing the leverage your LCAs have on your torsion bars. This negatively effects the ride by taking the torsion bars out of the preload range they were designed to work in. In combination with that, if you crank too far your UCAs have very little room left between them and the lower bump stops, reducing downward travel.


The only way you can add actual pre load or tension to the TB (besides adding weight to the truck) is if you would have enough adjustment that you could raise the truck to the point that the UCA was tight against the bump stop and you continued to turn the bar. Since the suspension couldn't move anymore, you would _then_ be twisting the bar with the adjuster. This is the only way to add pre load. When you change keys or turn the adjuster bolt, your ROTATING THE ENTIRE BAR, and pivoting the suspension downward in relation to the frame. As long as the suspension can move AS YOU ROTATE THE BAR, your *not *adding actual preload to the bar. Although when you do rotate the LCA down in relation to it's pivot point, it does slightly change the "leverage" factor the suspension has on the T-bar and will add a little resistance for the LCA to twist the bar, but it's not pre load. I covered some of this in a previous post before also.



millsaps118;495962 said:


> NBI...just the opposite of what your thinking, when you raise the front via t-bars it brings the LCA (lower control arm) closer to the bump stop. You increase travel height and lose downward travel. That's why you get a ruffer ride, the LCA is closer to the stop impacting it much sooner than if it were set at stock height.


This is correct EXCEPT the bump stop is under the UPPER contol arm, not the lower one. The only travel limiter on the LCA is the shock. Which will also give a rough ride if it's too short. The two major causes of a rough ride after a T-bar adjustment are 1) Like millsaps says here, that the suspension physically runs out of droop travel (either by the bump stop or the shock travel. And 2) due to changing the arc that the suspension travels which also changes the pivot point that the T-bar has on the LCA. (I described a bit about this in a previous thread.)



saabman;495960 said:


> When you crank the bar, it moves the lower control arm down (raising the truck). This moves it away from the bump stop. When the jacked suspension compresses, the lower control arm has more distance to travel before hitting the OEM bump stop. As such, it sweeps a greater angular distance, it will twist the TBAR more than it could of when the lower arm sat closer to the bump stop. This is why new bump stops are offered on some lift kits. They make sure the suspension does not "over travel". If you the suspension twists the bar to much, it will break.
> 
> This is similar to putting lift blocks on a leaf springs and not lengthening the bump stops. In this case the spring can "invert"


Generally speaking saabman is also 100% correct...but the T-bars GM uses are more than strong enough to take any amount of "twisting" that the truck would ever see even with the bars "cranked" or a set of keys installed as the suspension can only travel so far up and down, and the bars have more than enough elasticity to cope with the range of motion that these trucks have.

So what it all boils down to, and to answer the original question, sure "crank" them up all you want, it won't have a direct impact on the life of the bar. Might damage the shocks if they're too short or shorten the ball joint or CV joints life some, but it won't be a direct cause of a broken bar.


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## saabman (Sep 20, 2007)

My lanquage is colored by car setup and my summer pursuit of historic racing and autocross.. Droop stops are the rubber bumpers that limit downward travel of suspension (as it found when the front end is off the ground and the suspension is "drooping"). Bump stops limit upward travel under compression.

As I have stated in other threads, I much prefer to use the Timbren helper spring than changing the static ride height. My plow is off the truck more than it is on it, and I would not like the front end posture that is often associated with TBAR adjustment to compensate for plow load. My truck sits level with the plow on or off. As you can see from the picture I posted the Timbren does not contact the LCA at rest and most often does not contact it in unladen driving.

I have only been on this board a couple of months and this topic comes up in different flavors over and over again.


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## JD Dave (Mar 20, 2007)

I new B and B would make sense of it all!! Thanks.


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## B&B (Nov 4, 2006)

saabman;496163 said:


> My plow is off the truck more than it is on it, and I would not like the front end posture that is often associated with TBAR adjustment to compensate for plow load. My truck sits level with the plow on or off.


 My plow is off most of the time too..as is many guys. The T-bar discussions seem to mostly come from the fact that the GM trucks set low in the front to begin with (some more than others). And after you install a plow, they appear even lower. Most guys just want the truck raised a bit in the front, not "cranked" in order to carry the plow at a higher height in relation to the ground. It's when they're looking to go beyond that point is when the questions start to come up.

My practice when doing a plow install is to FIRST level the truck, and then add the plow. I never turn the bars farther than necessary to level the truck _*unladen.*_. If it doesn't have enough height after the plow install, I then add the Timbrens.


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## millsaps118 (Aug 13, 2006)

B&B..... sa-bout time you chimed in. 

These torsion bar Q's have been beaten' like a dead horse. I think this is a topic that will always be viewed and told by a million different opinions. 

One person says turning your tbars won't make 'em break, the other guy will say, yeah they will cause 'em to break. It's a never ending debate. IMO I still think that turning them all the way in (up) will eventually cause them to break. JM.02


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## B&B (Nov 4, 2006)

millsaps118;496270 said:


> B&B..... sa-bout time you chimed in.


 Had too, JD was gettin worried...



millsaps118;496270 said:


> These torsion bar Q's have been beaten' like a dead horse.


 I agree, the T-bar discussions have been around since the first ones came out...but sometimes it just takes a little different explanation, or an extra example than the last thread for the next guy to understand it. So I feel all questions are worth an explanation, or at least a referral to a previous thread. 



millsaps118;496270 said:


> I think this is a topic that will always be viewed and told by a million different opinions.
> One person says turning your tbars won't make 'em break, the other guy will say, yeah they will cause 'em to break. It's a never ending debate. IMO


 I agree with ya there too mill, but....my explanations aren't just my "opinion".. believe me, I know a thing or two about the T-bar suspensions on the GM trucks.


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## Detroitdan (Aug 15, 2005)

I'm just glad that my impression of how turning the bars up actually affects the t-bars tension turned out to be right. After reading some of the posts I began to question if I was actually misinformed too.


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## ticki2 (Jan 10, 2006)

I agree with ya there too mill, but....my explanations aren't just my "opinion".. believe me, I know a thing or two about the T-bar suspensions on the GM trucks. [/QUOTE]

B&B , I'd like your thoughts on another part of the front suspension , the lower bump stop ( or jounce as GM calls it). In stock form this jounce is in contact with the LCA in the static position. If the TB's are turned to raise the front end they no longer touch. Same thing with the timbrens in the above post. My thought is that they are part of the suspension design and relieve some of the torque on the bars when the front end comes down . Having a space there may be contibuting to the harsher ride that some experience with the TB turned up. Do you think they should be repositioned (blocked down) to contact the LCA if the TB are turned up ?


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## saabman (Sep 20, 2007)

I dont have experience with the front suspension of a great many of these trucks, but it seems wrong the LCA, to rest on the bump stops at rest. The factory stop is very hard rubber. It is truely there to stop the upward movement of the LCA. When the LCA hits the stop, suspension travel is all over. If is starts contacting the stop, then it effectively defeats the shock/spring on upward excursions (from the rest position). Most suspension are set up to allow up and down motion from the static position. 

As a general rule, the higher the spring rate the closer you can statically set the supension to the bump stop. In a classic tuned sports car suspension you LOWER the front spring (shorter spring w/ higher rate) and modestly trim the bump stop. The latter must be done to allow the suspension to compress from the new squat stance.


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## ticki2 (Jan 10, 2006)

It doesn't seem that these "bump stops" on the GM's are bump stops in the traditional sense , they are more like rubber springs similar to timbrens that will also limit total travel. They are located close to the pivot point so they don't have to compress very much to be functional. When I installed the timbrens on my Dodge they made contact at the rest position. Still learning


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## NBI Lawn (Oct 15, 2007)

saabman;496077 said:


>


This is what I was trying to say. When the T-bar is cranked up it will push the LCA down making the distance to the bump stop greater.


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## Motorman 007 (Jan 11, 2005)

B&B;496306 said:


> but....my explanations aren't just my "opinion".. believe me, I know a thing or two about the T-bar suspensions on the GM trucks.


Does that say it all or what??


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## B&B (Nov 4, 2006)

ticki2;496581 said:


> B&B , I'd like your thoughts on another part of the front suspension , the lower bump stop (or jounce as GM calls it). In stock form this jounce is in contact with the LCA in the static position. If the TB's are turned to raise the front end they no longer touch. Same thing with the timbrens in the above post. My thought is that they are part of the suspension design and relieve some of the torque on the bars when the front end comes down . Having a space there may be contibuting to the harsher ride that some experience with the TB turned up. Do you think they should be repositioned (blocked down) to contact the LCA if the TB are turned up ?





ticki2;496639 said:


> It doesn't seem that these "bump stops" on the GM's are bump stops in the traditional sense , they are more like rubber springs similar to timbrens that will also limit total travel. They are located close to the pivot point so they don't have to compress very much to be functional. Still learning


 tiki2, I have to say I think you have a superb understanding of the GM T-bar suspension and your thinking is right on line. And you are correct, GM does refer to the lower "bump stop" as a jounce bumper. Personally, I still use the term "bump stop" as it's easier for guys to grasp, but jounce is the correct term. You are also correct that the jounce bumpers are not used in the traditional sense in this application (as well as other non GM stuff). No longer using the bump stop in the traditional sense was one of the reasons GM switched to the term "jounce" as they aren't just there to stop the upward travel of the suspension and as you suspect, They are in fact actually used along with the T-bar to create a progressive rate in the suspension. It's very cost prohibitive to make a progressive rate T-bar (although they are out there). So GM decided to incorporate the JB directly into the effective spring rate of the suspension by engineering it to be in contact with the LCA at ride height. Thus making the spring rate of the bar stiffer as the suspension compresses (exactly like a progressive coil or leaf spring does). The JB itself is also progressive, it gets stiffer the more it's compressed. It actually works quite well for ride comfort and handling. Have you ever seen me refer to the term "Z-height" in some of the other T-bar threads? The Z-height is actually an important measurement on these trucks as it determines the relationship between the LCA and the JB thus setting the correct effective spring rate. I think by now to most guys it's quite clear how sophisticated these IFS trucks really are since all the components are interrelated with each other. Changing one thing on them, can and will affect the operation of the other components that make up the suspension.

You also mentioned moving the JB down to reestablish contact between it and the LCA, and while it sounds like a good idea, in practicality it's not quite that simple. Once you raise the height of the truck with a T-bar adjustment, it changes the angle of the LCA in relation to the JB mounting point on the frame. If you only space it down, it will contact the LCA at an incorrect angle and will damage the JB within a period of time. If you tip the JB in toward the center of the truck to reestablish the correct angle with the LCA, it moves the JB too close to the LCA pivot point, in the process removing a certain amount of the compression traval out of the suspension...not good. Anybody that has installed a set of Timbrens on one of these trucks knows that they also include a wedge to tip the Timbren inwards so it contacts the LCA at the correct angle, so why can't you do the same thing with the JB? Because when you move the JB closer to the LCA pivot point it loses a good amount of it spring rate effectiveness since the LCA now has much more mechanical leverage on it from moving it closer to the pivot point. It could still be used effectively as a bump stop, but not as an additional means of spring rate (like a Timbren is used for). The Timbrems on the other hand work a little differently due to their composition, that's why they're a better alternative than the stock JB in this application. Spacing the Timbrens down is also a good idea, but you have to be careful how far you actually move them down or they greatly limit the compression travel in the suspension. It would have to be done on a truck by truck basis for however much the truck was raised over the stock height.


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## saabman (Sep 20, 2007)

B&B, that is a facinating and informative read. Makes me more comfortable with the contact that LCAs make with Timbrens since from your description that is just what they did on the "jounce stops".


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## B&B (Nov 4, 2006)

saabman;497359 said:


> B&B, that is a facinating and informative read. Makes me more comfortable with the contact that LCAs make with Timbrens since from your description that is just what they did on the "jounce stops".


 Glad to hear you found it useful saabman. Usually when I get into the details on why IFS isn't as simple as it looks (not that it's complicated either LOL), I usually get the "deer in the headlights" kinda look from guys.. But there's plenty of guys out there that have been running these trucks for years and don't totally understand why they work or don't work the way they should...and is the reason I have no problem with taking the time to try and explain it as best I can. You having experience in the racing suspension field, have probably encountered the same types of situations as far as explanation goes I'm sure.

It's not rocket science...it's just force and geometry, both of which can be taught.


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## ticki2 (Jan 10, 2006)

B&B
Thanks , that is one of the clearest explanation I've heard to date. At the risk of being a pain in the a** , one more question. I have not installed timbrens on an IFS yet. In the stock height ( Z height spec ) do you know if the timbrens contact the LCA ?


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## saabman (Sep 20, 2007)

B&B said:


> You having experience in the racing suspension field, have probably encountered the same types of situations as far as explanation goes I'm sure.


You've got the right. Explaining topics like ackerman, anti-dive, and caster are some of my favorite blank stare evokers.



ticki2 said:


> I have not installed timbrens on an IFS yet. In the stock height ( Z height spec ) do you know if the timbrens contact the LCA ?


It depends on how far you have the TBARS cranked. That is my truck in the picture in this thread. I did not crank the TBARS, but I think the previous owner may have. Which is surprising to me given the fact that it did not have a plow prior to the one I installed.


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## B&B (Nov 4, 2006)

Glad you also found it informative ticki. You ask excellent and highly intuitive questions...

Specifically on a 2500HD, if the truck is at the recommended Z spec, they will set on the Timbrems just a bit...and is totally normal.

And also just to specify for reference, just because the truck was bought new at the dealer or the truck has never had a T-bar adjustment since new (that the owner is aware of) doesn't necessarily mean that the truck is at the correct Z spec. Many truck's roll off dealer lots with the incorrect Z height. That's why theirs variation in the fact that some guys will find their trucks do set on the Timbren and some don't.


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## B&B (Nov 4, 2006)

saabman;497534 said:


> You've got the right. Explaining topics like ackerman, anti-dive, and caster are some of my favorite blank stare evokers.


My favorites are dive, lift, squat and fore/aft dynamic load transfer...they usually think I changed the subject to aerobics when they weren't paying attention..


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## JD Dave (Mar 20, 2007)

B&B;497546 said:


> My favorites are dive, lift, squat and fore/aft dynamic load transfer...they usually think I changed the subject to aerobics when they weren't paying attention..


Ahhhhh B And B found a friend he can talk shop with.


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## Motorman 007 (Jan 11, 2005)

B&B;497546 said:


> My favorites are dive, lift, squat and fore/aft dynamic load transfer...they usually think I changed the subject to aerobics when they weren't paying attention..


You guys are starting to scare me.......


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## ticki2 (Jan 10, 2006)

I agree, the T-bar discussions have been around since the first ones came out...but sometimes it just takes a little different explanation, or an extra example than the last thread for the next guy to understand it. So I feel all questions are worth an explanation, or at least a referral to a previous thread. 

[/QUOTE]

B&B , can't tell you how much I appreciate that attitude . So many times on this and other forums important questions get turned into pi**ing matches. and the ones with real knowledge just stay out of it. I can see why you are respected here.

Thanks also for the info in your responses , it will help a great deal in setting up the suspension for my needs.


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