diff service

**jz28** · 05-12-2008, 08:57 PM

i need to service my diff but need some input on wat kind of oil i should use..
another question is does the stock diff have a drain plug? or what would i have to do?

**Spikito** · 05-12-2008, 10:32 PM

I dont know if the 98-02 are different than the 93-97, but on mine there isnt a drain plug, you have to pop the cover off. and that i dont know anything about. Think i use something like 80 weight in my diff, i just topped it off today and i cant remember.

**konigandy6** · 05-13-2008, 02:50 AM

Just stick with the GM synthetic fluid. It is pretty pricey but worth it!

**txturbo** · 05-13-2008, 05:48 AM

No drain plug. You have to remove the rear cover, or suck it out through the fill hole.

**346ci** · 05-13-2008, 08:43 AM

You'll have to pull the rear diff. cover off to drain it, so you will need a new diff. gasket. Refill it with 75W-90 gear oil; I highly recommend GM synthetic although it's $20 a bottle and I think you will need 2 to fill the diff back up.

**camarojunky74** · 05-13-2008, 09:24 AM

you can just suck it out you will save time this way, i use mobil 1 75-90 synthetic and its a little over 2 quarts to fill it back up,

if you decide to pop the cover, the gasket works the best as stated above,

good input here guys.
also there is a possibility you may have the auburn rear, if your car is slp optioned you will find the options in the pass door, if thats the case you will need some lsd additive, and honestly the motorcraft shit at the ford dealer

**BrntWS6** · 05-13-2008, 09:49 AM

I always just suck it out the fill hole with a baster. Saves time and I don't have to worry about leaks in case I didn't seal up the new gasket correctly.

**konigandy6** · 05-13-2008, 11:49 AM

In the long run it is always good to change the gasket every time you your diff. service. This is just cheap insurance for leaks and you get to inspect your gears with the cover removed.

**aerojt** · 05-13-2008, 02:04 PM

Maybe I am wrong, but don't all of the ss/z28 rear ends need limited slip additive? Thanks!

**SSMichael** · 05-13-2008, 02:44 PM

I have a 2002 SS heres what my Owners Manual said.
STANDARD DIFFERENTIAL
Use SAE 75W-90 Synthetic Gear Lubricant ( GM Part No. 12378261 )

LIMITED-SLIP DIFFERENTIAL
Use SAE 75W-90 Synthetic Gear Lubricant ( GM Part No. 12378261 )
Add 4 ounces of Limited-Slip Differential Lubricant Additive
( GM Part No. 1052358 )
And all that is for a completely refill after draining.

**02fbody35th** · 05-13-2008, 04:25 PM

definatly us the diff addative, when i did mine i forgot to put it in and it squeeled until i put it in then it went away

**jz28** · 05-13-2008, 09:07 PM

Thanx for all the info guy's. helps alot.

**Spikito** · 05-14-2008, 03:13 PM

where can i get this additive?

**thearborbarber** · 05-14-2008, 04:45 PM

Most parts stores carry one brand or another of posi additive. My local parts store carries ATP brand and Kendall brand. I have't sen any difference between the two.

**chaosinfinite** · 10-16-2008, 09:03 AM

Good information to know.. I am going to be doing the rear diff this weekend. Does anyone know how much the additive is? What if you buy Mobile 1 syn...does that come with the additive?

**konigandy6** · 10-16-2008, 09:14 AM

Originally Posted by chaosinfinite

Good information to know.. I am going to be doing the rear diff this weekend. Does anyone know how much the additive is? What if you buy Mobile 1 syn...does that come with the additive?

No, it does not come with the additive, you will have to pick that up at your dealer. I dont believe it is that pricey.

**chaosinfinite** · 10-16-2008, 11:12 AM

I seen some of that additive at AdvanceAuto...is it the same quality? Or should I still pick some up from the Dealership?

**konigandy6** · 10-16-2008, 11:40 AM

Originally Posted by chaosinfinite

I seen some of that additive at AdvanceAuto...is it the same quality? Or should I still pick some up from the Dealership?

Completely your call, I only use the dealership stuff.

**Crimson Sin** · 10-16-2008, 11:51 AM

Not much you can get at Advance is OEM level. If you want OEM don't go Advance/Schucks/PepBoys. NAPA / Carquest may have better, then again maybe not. Only thing truly GM is GM, for a few bucks more. I would go GM.
Just my 02.

**jcws6** · 10-18-2008, 08:28 PM

I use the $4 stuff at AutoZone with Mobile1 synthetic oil. It's called "Trans-X Posi-Trac Limited Slip Gear Oil Additive." It says on the label "Meets OEM recommendations... GM# 1052358."

The additive is just a friction modifier that makes the oil more slippery for clutch-style posi differentials. A lot of people say a good synthetic is slippery enough to do the same thing, but I use the additive anyway (it doesn't hurt).