differential fluid

[scottac]

I am doing the differentials this weekend and was wanting to know how much fluid to buy.

 

I am buying at the gm parts department. the guy in the parts department didn't know how much I would need.(gofigure right).

 

I am doing the front and the rear. and will also be doing the automatic transfer case.

 

anybody got experience with this and know how much of each fluid I will need.

 

thanks in advance for all the replies.

[Black02Silverado]

If you have a 1500 then you will need just under 2qts for the front diff and just over 2qts for the rear, and the transfercase takes just under 2qts as well. At least my autotac did.

 

Why go to GM for the fluid? You can get a good synthetic at your local parts store. Do a search on here and read all about it, there is a ton of good information on here already posted.

[JayMan]

Well, assuming it's a 1999-2003 GMC or Chevy pickup/tahoe/yukon, etc:

 

Front axle: 3.5 pints or 1.75 quarts

Rear axle: 2.1 quarts claimed, will hold 2.7 quarts

Total gear oil: Get 5 quarts

AutoTrac transfer case: 2.3 quarts, so you will need 3 quarts

 

You need a synthetic for the rear axle, there should be a tag next to the fill plug stating so. The Goodwrench Synthetic 75W-90 is like $24 / quart. A substitute is Amsoil gear oil 75W-90 (About $9/qt) or Mobil 1 75W-90 gear oil ($5/ qt). If you have the G80 GovLok rear axle, it wouldn't hurt to put in a tube of friction modifier, something like CRC Trans-X PosiTrak LS additive.

 

The front axle needs a 80W-90 GL-5. There was a TSB a while back warning to use a synthetic 75W-90 if the temps drop below -5 F in your area. I would run a synthetic in the front axle anyway for better wear protection.

 

Note: you may want to take the rear cover off the axle to clean the magnets off. Depending on how many miles you have on, especially if this is the first gear oil change, there will be a lot of filings on the magnets. Fuzzy filings are normal, chunks and actual pieces of gear are NOT normal.

 

You may want to remove the skid plate, if equipped, to make servicing the front axle easier. The front axle drain plug has a magnet on it, and I bet it will be full of black sludge and heavy filings. Mine was at only 600 miles! If it makes you feel better, refill with a cheap 80W-90 like I did, drive it a few days, and drain again. Keep doing this until the magnet stays clean, then refill with your gear oil of choice.

 

You may want to invest in a gear oil pump of some sort, the type that screws onto the bottle of gear lube, to make filling the front axle easier. I have pails of commercial synthetic gear oil around my shop, so it's too easy for me to just put the fill nozzle into the fill hole, give the pail pump 2-3 pumps, and it's full.

 

If the AutoTrac fluid drains out red (Older factory fill) or appears dirty, the replacement AutoTrac II fluid is blue and has higher detergents. Wouldn't hurt to drain and refill again after a week or so of driving. MoutineerTom has excellent guides on the gear and autotrac fluid change, look at the left frame of this forum under "Guides."

 

FWIW: I did the initial service at 600 miles: Front and rear axles, trans, and autotrac. After towing the first time, did the rear axle 600 miles later. Did them again a year later with about 12,000 miles on it. The supplemental GM GoodWrench SmartGuide suggests initial axle service at 3,000 miles, then every 12,000 miles. If you tow for the first time, 600 miles after.

 

Why do you want to buy from this dealer if they don't even know how much fluid it holds? YIKES!

 

Good luck! All the fun in owning a truck is getting oily and greasy!

[JayMan]

Hey everybody:

 

Can anybody offer a reasonable explanation of why GM wants the LD rear axle fluid an inch or so below the fill hole? The bigger axles in the 1500HD, 2500LD/HD, and 3500HD are supposed to be filled to the fill hole.

 

I was always taught to fill it to the fill hole and let the excess seep out. I've always filled mine to the top this way and have never had any problems after 38,000 miles of driving.

 

Are they worried about thermal expansion and the excess peeing out the vent tube? Since they require a synthetic 75W-90 gear oil, that stuff is very stable and has little expansion under heat. Also, the vent tube on my truck is routed all the way to the gas fill. Have never seen gear oil gushing out my filler cap yet.

[JayMan]

If you have a 1500 then you will need just under 2qts for the front diff and just over 2qts for the rear, and the transfercase takes just under 2qts as well. At least my autotac did.

 

Why go to GM for the fluid? You can get a good synthetic at your local parts store. Do a search on here and read all about it, there is a ton of good information on here already posted.

 

Geez, why do we always post out of synch?

 

Had better chat before the next post!

 

BTW: I see that Amsoil has FINALLY offered an Allison TranSynd-compatible fluid. Bout time, that Castrol TranSynd was on the way to keeping Castrol and Allison on the gravy train.

[scottac]

thanks for the replies guys. the reason I am going to gm for the parts is becasue I went to pep boys for the gear oil and all they had was 80W-90. will any 80W-90 be sufficient.

 

I was also going to buy a gasket for the rear diff whil I was there and they didn't have that either.

 

I would really like to buy a cheaper product if it will do the same job.

 

any suggestions on parts stores that will carry the products I am looking for.

 

thanks.

[RyanbabZ71]

Can anybody offer a reasonable explanation of why GM wants the LD rear axle fluid an inch or so below the fill hole? The bigger axles in the 1500HD, 2500LD/HD, and 3500HD are supposed to be filled to the fill hole.

 

to much gear oil is bad. the fluid wont be able to cool as well and with the gears turning even if your diff is low there will be a splashing of fluid which will be enough to lubricate the gears.

[Black02Silverado]

thanks for the replies guys. the reason I am going to gm for the parts is becasue I went to pep boys for the gear oil and all they had was 80W-90. will any 80W-90 be sufficient.

 

I would really like to buy a cheaper product if it will do the same job.

 

any suggestions on parts stores that will carry the products I am looking for.

 

thanks.

Scottac,

 

Just get a brand name GL5 rated 80w-90 for the front axle.

 

I would not put a regular (dino) oil in the rear. GM put synthetic in there for a reason and I would stick with that. You can get Mobil 1 GL5 rated gear oil at Auto Zone and Wal-Mart here carries it. That would be your best bet since it is easy to get and if you think about it cost isn't all that bad. For the number of times you would change out the fluid the cost is minimal.

 

There are posts on here about using the additive. It doesn't hurt to put it in. It just covers yourself on potential problems that could "possibly" occur if you didn't install it. I can't speak for Mobil1 gear oil but I do Know AMSOIL has it already in there gear oil and in some cases more of the additive had to be added to it as well. This was in an Eaton Posi unit not the G80 that is in our trucks. In anycase it will not hurt a thing.

 

These 2 links are the 2 oils that AMSOIL has for the rear diff that is GL5 rated.

 

Series 2000 75w-90

 

Regular synthetic gear lube

 

The second link show a 80w-90 oil that is GL5 rated as well which works for the front diff.

 

So if you can find Penzoil, Castrol a good brand name regular oil for the front, just make sure it is GL5 rated. I live in a small town so not to many stores to choose from. Sorry I couldn't help there.

 

As for the transfer case. The Auto Trac II that the dealer carries is the only fluid available for an Auto Transfercase. If you fluid is blue when you drain it then you can't put regular Dextron in. You have to use the Auto Trac II. It was $5. a qt at the dealer here. Like "Jayman" stated above you can use it in place of regular Dextron and in some cases it has helped with individuals having a clunk sound in their drive tran. Again this site is awesome, do a search and you can find a ton of great information on here. Now if your like me an stuck with dial up, just be patient.

 

Hope this helps.

[JayMan]

thanks for the replies guys. the reason I am going to gm for the parts is becasue I went to pep boys for the gear oil and all they had was 80W-90. will any 80W-90 be sufficient.

 

I was also going to buy a gasket for the rear diff whil I was there and they didn't have that either.

 

I would really like to buy a cheaper product if it will do the same job.

 

any suggestions on parts stores that will carry the products I am looking for.

 

thanks.

If you never drive in temps below 0 F, like Black02Silverado sez, any 'ole GL-f rated 80W-90 should work fine in the front axle. GM will soon be issueing a TSB requiring a synthetic 75W-90 in the front axle if operated in cold temps.

 

If you have a regular floor-shift transfer case, use the Dexron III ATF. If you have the AutoTrac push-button transfer case (There will be a button "Auto 4WD" in addition to the usual choices) then you MUST use the dealer-specific AC Delco AutoTrak II fluid. Using the wrong transfer case fluid in the AutoTrac will cause problems with the clutch packs inside, not the least of which will be that CLUNK CLUNK sound.

 

I've only been able to find the rear axle cover gasket at my GM dealer. It was $6 and even came Shrink Wrapped For My Protection.

[JayMan]

Can anybody offer a reasonable explanation of why GM wants the LD rear axle fluid an inch or so below the fill hole? The bigger axles in the 1500HD, 2500LD/HD, and 3500HD are supposed to be filled to the fill hole.

 

to much gear oil is bad. the fluid wont be able to cool as well and with the gears turning even if your diff is low there will be a splashing of fluid which will be enough to lubricate the gears.

I've towed 7,200 lbs extensivly in +95 heat with no problems. I asked my local dealer service manager about this issue this morning over coffee: he claims it makes servicing easier!

 

The technician dumps in 2 bottles (Two quarts) of the expensive GoodWrench gear oil and is done. They actually make a habit of topping off the axle, no matter if LD or HD.

 

Run that low, the pinion bearing will have to depend on splash for lubrication. In very cold temps, I would worry about how well the pinion bearing gets "splashed" in oil the consistency of taffy. Keeping the axle topped off will keep the pinion bearing immersed in gear oil.

 

Same as the wheel bearings at each rear wheel. If you top off the axle, they will always be bathed in oil.

 

Some folks may wonder about seal leaks run this way. If you buy a Mag Hytek rear cover, they actually recommend overfilling the axle to keep the bearings immersed in gear oil!

 

My heavy equipment runs with immersed seals and I've had 2 seal leaks in 20 years (Bad seal from new). I had a bad pinion seal from new on my GMC. I noticed the drips a week after taking delivery, and they replaced the pinion seal under warranty. No leaks since, and I've always topped the gear oil off to the fill plug.

[scottac]

alright one more question. Gl-f rated or gl-5 rated. or is there a difference.

[bigdogs]

JayMan, when you hear they did issue the TSB for the front axle, please let me know, I'll bring it into the dealer and let them change it for free

[scottac]

what is the TSB and Where can I find 75W-90. I don't want to buy the overpriced gear oil from the dealership if I don't have to.

 

I have been to Wal-mart and to Pep-boys. neither place carries the 75W-90 ssynthetic.

 

anyway. thanks for all the replies.

[gnutruk]

On my gear oil changeouts (done them all), I went with the GM brand for one reason and one reason only.

 

Given how GM and their stealerships are prone to jump on any little thing you might do for an excuse to deny warranty work, I figured that having the receipts to show that I used EXACTLY the stuff they recommended would take just a little bit of wind out of their sails, if I ever got into a warranty dispute with them.

 

But after my three years - 36,000 are up, then I will be following some of the suggestions posted above on this topic.

 

quote: << Can anybody offer a reasonable explanation of why GM wants the LD rear axle fluid an inch or so below the fill hole? >> quote

 

Ryanbab answered that one:

 

quote << to much gear oil is bad. the fluid wont be able to cool as well and with the gears turning even if your diff is low there will be a splashing of fluid which will be enough to lubricate the gears. >> quote

 

A small trick that someone on this site mentioned quite awhile ago for checking the correct fill level on the 1500 G80 rear diffs. Take one of your standard type allen keys and dip it in there. The length is just about perfect for getting that approx. one inch depth below the hole.

 

For sure take off the rear diff. cover and clean that magnet. Removing the fuzz and generally tidying up in there is good for your confidence. Do this twice, the first change as soon as you can, the second at about 40,000 or 50,000, or immediately after your first big tow, and you will have a "no hassles" rear diff. for the entire life of the truck.

 

ALWAYS replace the gasket with new: that's just about the cheapest little insurance you will ever buy. Rear diff. cover gasket for the year 2002 4wd 1500 10-bolt G80 locker is GM Part #26066456.

 

Then, torque down the diff. cover bolts to the recommended setting. I think it's supposed to be 40 N-m, which is 30 ft. lbs. Tighten the bolts in a crosswise pattern. Last, fill with what you choose. Mine took 2.4 qts. Came in at 3/4 inch below the hole, truck parked level.

 

THEN, THIS IS IMPORTANT : go for a moderate drive so the rear diff. gets warm. Come back, let it cool, and then re-check those bolts to the correct torque. What happens is that things warm up and re-seat a little bit. The gasket seats in. You want to cycle it through once like that so everything gets right.

 

Rear diffs. naturally warm up a bit in use. A healthy diff. gets warm to the hand, but never hot. If you can't touch that rear diff. cover, you got problems. Even if the gears aren't over-heated, the fluid will be shot for its lube qualities. Even synth.

 

Front two diffs. (i.e. front diff. and transfer case) are simpler. No housings to remove or replace. Just drain and fill. Someone gave all the amounts above.

 

gnutruk

[JayMan]

alright one more question. Gl-f rated or gl-5 rated. or is there a difference.

Geez, I'm sorry, my bad!

 

I type real fast and sometimes I do hit the wrong key ...

 

I actually did mean a GL-5 rated gear oil. Sorry.