# Fluid changes



## RichG53 (Sep 16, 2008)

I searched but did not find what I was looking for....I have an 01 2500 HD ... I would like to know what fluid to use in the diffes I have posy or locking rear..I was told by dealer that they use Mobil synthetic...Do I use the same in front & rear .. How much in each to drain and refill ..I would also like to know what to use in tranfer case..Manual says Auto Trak II fluid...How much for a drain & refill... How much to drain and refill transmission with filter...


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## B&B (Nov 4, 2006)

Any good name brand synthetic fluids are fine, doesn't have to be Mobil 1. The rear diff will be factory filled with synthetic, but not the front diff...but synthetic in the front isn't a bad idea as well. Use 75W-90 in both diffs.

There has been much confusion as to the correct fluid to use in the T-cases in these trucks as I'm well aware that GM themselves for a time recommended the Auto Trak fluid in them....even though they *are not *an auto style T-case. They originally called for Dexlll ATF...and then changed their mind. It then seemed that GM felt that the Auto Trak fluid was the best thing they had for a while so they then recommended that. But has now superceded their info to use their MTF (manual trans fluid GM p/n 88861800). But ultimately you can run any brand of manual trans lube, doesn't have to be GM's. Many guys run Royal Purple's Syncromax MTL with excellent results. Redline's MTL is fine as well. Many home brew guys even run straight 5W-30 engine oil or a mix of ATF and 5W-30 together.

For APPROX capacities your going to need:

4 qts for the rear axle
3 qts for the front diff
2 qts for the T-case
8 qts for the trans fluid & filter change


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## RichG53 (Sep 16, 2008)

...MTF is what weight.. ? ? ? Thanks a lot I could not find anything in my manual...I will print this out for future reference.......Does the oil need to be detergeent or non....MTF is what weight .. ? ? ? ?


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## BigLou80 (Feb 25, 2008)

B&B
thanks for the info I have been running Autotrak2 fluid which is expensive and requires a trip to the dealer

Lou


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## B&B (Nov 4, 2006)

RichG53;592355 said:


> ...MTF is what weight.. ? ? ? Thanks a lot I could not find anything in my manual...I will print this out for future reference.......Does the oil need to be detergeent or non....MTF is what weight .. ? ? ? ?


MTF = Manual Transmission Fluid.

MTF isn't based on weight/detergent/non detergent etc. If it's MTF it's...well MTF. No choices..

But strictly for comparison purposes it's approx the same viscosity as ATF.


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## RichG53 (Sep 16, 2008)

I was referring to the motor oil you said some were using deter or non....? ? ?


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## B&B (Nov 4, 2006)

RichG53;592382 said:


> I was referring to the motor oil you said some were using deter or non....? ? ?


 Doesn't matter as far as the transfer case is concerned. And I know of no oil manufacture that currently makes 5W-30 *non detergent *oil with the correct classifications for automotive use anyway.


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## tuney443 (Jun 25, 2006)

To further clarify{or muddy up the water,depending on how you look at it},the manufacturer of the transfer case actually recommends 5/30 synthetic engine oil,GM does NOT however.They state in their article that ATF vaporizes too easily in their TC and to use 3 qts.of oil.You have to add that third qt.into the speed sensor hole right above the regular fill plug.I've done this on my '06 Dmax for about a year now and all is well.


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## aeronutt (Sep 24, 2008)

I've been very pleased with the Amsoil synthetics in my truck. Contact your local dealer for applications or look it up yourself on their website. Don't pay full retail. It's a stupid marketing stunt, but if you pay $10 to be a "prefered customer" you end up saving much more than $10 on your first order.

I order mine online through a dealer I met at another forum. THIS LINK will let you order directly by mail order and give my dealer the credit. I make nothing from this endorsement, just spreading the word...


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## RichG53 (Sep 16, 2008)

Well B B do you have ant comments on the above replys... ? ? ? ?


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## B&B (Nov 4, 2006)

I'm well aware that NVG does now recommend 5W-30 SYNTHETIC in these 261/263 T-cases due to previous problems with misting. Which is why GM no longer recommends the Dex3 ATF that they once did like I previously mentioned. And thats the trick, the synthetic part. The synthetic fluid (whatever type it may be) solves the misting issues that they had with these T-cases when they were speced to run on straight ATF.

GM's MTL is synthetic, AutoTrac ll is synthetic, Royal Purples Symcromax is synthetic, Redlines MTL is synthetic...and all of these are fluids that I recommended. Do you see the trend here? 

As long as you run a synthetic fluid there is no need to overfill either. Since with the synthetic you have no misting issues.


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## brad96z28 (Aug 21, 2005)

Wonder why they dont run dex 6 in them? Maybe thats whats next. Anyone wana bet?


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## B&B (Nov 4, 2006)

brad96z28;593560 said:


> Wonder why they dont run dex 6 in them? Maybe thats whats next. Anyone wana bet?


Possibly. But GM's speced Dex VI is not full synthetic (which again is what you want to run in these T-cases) it's a synthetic BLEND, as is some of the aftermarket classified Dex VI that meets GM's specifications for it.

But several of the aftermarket oil companies do now have a fully synthetic Dex VI. Amsoil is one I know.


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## brad96z28 (Aug 21, 2005)

Funny how must manufacturs leave out that little detail. (blend).


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## brad96z28 (Aug 21, 2005)

Valvoline dex 6 is full synthetic. I think Im gona flush my tranny with that actually.


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## ChevKid03 (Dec 23, 2007)

brad96z28;593674 said:


> Valvoline dex 6 is full synthetic. I think Im gona flush my tranny with that actually.


Just picked up a few quarts of this for my T-Case...


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## B&B (Nov 4, 2006)

brad96z28;593674 said:


> Valvoline dex 6 is full synthetic. I think Im gona flush my tranny with that actually.


If your talking about the Allison equipped truck in your sig Brad don't waste your time or money on a Dex VI fluid....use Allisons own Transyd or TE-295 fluid. Better fluid for your money.


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## brad96z28 (Aug 21, 2005)

Where do u get it from?


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## B&B (Nov 4, 2006)

brad96z28;593684 said:


> Where do u get it from?


Any Allison dealer will stock it since it is of course Allison recomended for their transmissions. Some places online have it as well if you search around.


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## brad96z28 (Aug 21, 2005)

How about amsoil Torque-Drive Synthetic? Made for the allison. http://www.smartsynthetics.com/articles/amsoil_torque_drive_synthetic_atf.htm


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## B&B (Nov 4, 2006)

brad96z28;593697 said:


> How about amsoil Torque-Drive Synthetic? Made for the allison.


Very good stuff as well.


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## 70monte (Feb 5, 2008)

I know that the newer trucks have different requirements than my two 98's but I'm still leery about using synthetics in the diffs, tranny, and engine. I bought my 98 ECSB Z71 brand new and switched over to Mobil 1 tranny fluid in the trans and Mobil 1 75W-90 diff fluid in both front and rear diffs at about 20,000 miles. The tranny started feeling like it was slipping and not shifting right. I switched back to regular Dextron III and the tranny felt normal again.

At about 55,000 miles my rearend started making noise. It wasn't very loud at first but by 75,000 miles it was pretty loud. I took it to a driveline shop and they discovered my pinion bearings and another type bearing in the diff were going bad. This was a truck that was never abused and hardly towed anything and the largest thing it had towed was a 5x10 utility trailer. Also my front diff makes some noise but I haven't had it looked at yet since its not very loud yet. I now run regular 80W-90 in both diffs. I don't have proof, but I feel that the Mobil 1 caused my early noise and diff problems.

I used to run Mobil 1 oil(switched over at 3,000 miles) in my 5.7L but after doing oil analysis for a two year period and my results not coming back that great, I switched to regular Havoline and my oil analysis results became very good. I didn't feel like I was getting my money's worth and my engine was noisier and used more oil with Mobil 1. I was a huge Mobil 1 fan at one time and synthetics in general but now I just stick to conventional oils.

If I ever buy a new truck again, I will probably have to reevaluate my feelings about synthetics since I think they are a requirement in some components now.

Wayne


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## B&B (Nov 4, 2006)

I'm not a big fan of the Mobil brand myself Wayne. I feel there's better out there. The Mobil name isn't what I feel it once was.

Many times on the older stuff when switching to synthetic they will get noticeably louder as most synthetic is a bit thinner for a given temp. The older stuff depended on the fluid viscosity to help with noise reduction..the thicker it was the quieter it would run. Front diffs are famous for it.

Not defending Mobil here, but I doubt the pinion bearing deal was strictly due to the Mobil gear oil...I've put a TON of pinion and diff carrier bearings in low mileage GM 8.5/8.6/9.5 rears. Just did an '06 1/2 ton Avalanche today with only 41,000 on the ticker. Sounded like a spinning coffee can full of marbles before the repair...as many of them do.

Differential bearings have been an issue off and on with the GM's for years. The worse ones are the '93-up half ton 8.5's. The 7 1/2-7 5/8 rears in the S10's/Blazers/Astros are bad for it (any year) also.


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## 70monte (Feb 5, 2008)

The guy who replaced the pinion and carrier bearings(thanks for jogging my memory on the other bearings going bad) told me he also repaired a ton of the 8.5 10 bolts. He told me that the reason they went out so much was that they were undersized for the job and that the design did not allow for larger bearings to be installed. He said that he hadn't had many repairs for the 99 and up new body style trucks.

My truck had a loud whining sound when letting off the gas between 45-55 mph. The truck now has 104,400 miles on it and so far the rear is still quiet. I guess I can expect to have to have this repaired again in the future Of course I have known people with similiar trucks with high miles and no noise and never had repairs, so who knows.

Wayne


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## Sydenstricker Landscaping (Dec 17, 2006)

Not to steal the thread......But since we are on the topic of fluids and changing them. What do you do if you cant get the plug out of the rear diff?? I tried and dont want to strip out the thing. And what is the easiest way to do the front diff?? Thanks


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## B&B (Nov 4, 2006)

Sydenstricker Landscaping;594930 said:


> Not to steal the thread......But since we are on the topic of fluids and changing them. What do you do if you cant get the plug out of the rear diff?? I tried and dont want to strip out the thing. And what is the easiest way to do the front diff?? Thanks


Generally what I do if the plug is un-removable (even after some heat or after welding a nut on it if possible) is to drill a new hole in the the cover and weld a new fill bung in the cover at the same height as the original fill hole.

Front diff is easy to drain just pull the plug with a 13mm. Filling can be a bit of a problem if your not filling with a bulk pump. If the gear oil you purchase has one of those small reducing nipples on it you can lightly clamp a 2 ft section of rubber or vinyl 3/8" hose on it and then squeeze it in through the wheel well.


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## Yaz (Apr 13, 2005)

Not to get of the topic to much with rear ends but there has been lots of posts on other sites that GM actually puts in the absolute min fluid from the factory in the diff. So when you drain it don't be surprised if you only get a little out of it. If you haven't checked it, do it ASAP. For every rear end they sell it adds up as a cost saving!

Also..keep and eye out for a pin hole leak from the pump rubbing from the inside out in the transfer case. Unfortunately it's way too common. :crying:


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## BigLou80 (Feb 25, 2008)

Yaz;595711 said:


> Also..keep and eye out for a pin hole leak from the pump rubbing from the inside out in the transfer case. Unfortunately it's way too common. :crying:


My pin hole leak turned in to a large hole, I realized when it only took a day to get a new transfer case housing that it must be a pretty comon problem


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## aeronutt (Sep 24, 2008)

It's VERY common. This is an item that SHOULD have had a multi-million dollar recall, but since it's not a safety issue they just fix 'em as they wear out. It's not a matter of IF it happens, it's a matter of WHEN.

There are a couple of repair kits available that put a hardened washer for the pump to rub against rather than the aluminum casing. There is also one that is basically a new rear half of the t-case with an improved bearing surface already machined in. Price ranges from $50 to $300 depending on which option you choose. The cheaper ones are better if you don't already have the leak. Here's a link that will get you started. A search at dieselplace.com for "pump rub" will give you a month's worth of reading.


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