Full synthetic in diffs on a 99 Suburban

[Ralph_S]

Is it a good idea? I read somewhere that you shouldn't do it because the additives in synthetic gear oil deteriorate the seals. Has anyone here used synthetic gear oil in an older GM truck?

 

[Boomer]

I used Mobil 1 in a 97 Chevy truck for years (almost ten) with no real issues.

 

[hounddog]

Do what? More old wives tales.I've been using synthetic gear oils for decades.

 

[Warstud]

That's a new one!

 

[JHZR2]

lol, have been running syn in my 98 S10 since new.

 

[Jim 5]

I ran synthetic in the front and rear diffs on my '98 Chev K1500, my 04 Chev Avalanche and my current 07 GMC Sierra. No problems.

If I'm not mistaken, GM trucks come from the factory with synthetic diff fluid if they were made for the Canadian market. That should give you the comfort you need.

 

[xxch4osxx]

I run Amsoil SVG in the front and rear diffs on my 2004 Silverado and there are no leaks at all.

 

[dparm]

If synthetic really caused the seals to deteriorate, don't you think they'd stop making it? And that no one would buy it?

 

[CharlieJ]

I have synthetic gear lube in my 1984 Rx-7. No worries.

 

[OVERKILL]

Many OEM's use synthetic diff fluid, like Ford for example. Have no fear using it.

 

[Steve S]

Syn works great in differentials . If a seal is going to leak it will leak no matter which oil is used. If you want to run a "dino" gear oil go to a Chevron oil jobber and get some Delo ESI gear lube. Delo ESI is about as good as most syn oils and is a dino oil prices. The syns do better in the cold.

 

[Pablo]

Originally Posted By: dparm
If synthetic really caused the seals to deteriorate, don't you think they'd stop making it? And that no one would buy it?


Bingo!

 

[Ralph_S]

There you go Pablo, straight from Amsoil.com

[3] 1988-99 models
Do not use synthetic lubricant in axles using RTV sealant.
Synthetic lubricant will chemically attack RTV sealant.
American Axle has only approved the use of Synthetic
Lubricant 75W-90 GM part no. 12378261, as follows:
a. All 8.6 inch rear axles are compatible.
b. All 9.5 inch rear axles built before mid-February 1998
(RTV sealant used to seal cover pan) are not compatible
c. All 9.5 inch rear axles built after mid-February 1998
(equipped with cover pan & gasket) are compatible.
d. All 10.5 inch rear axles built prior to March 3, 1999 are
compatible if axle shafthub RTV sealer is replaced with GM
gasket part no. 327739.
[

 

[Ralph_S]

That's why i specified 99 Suburban. I'm aware a lot of manufactures have been using synthetic gear lube in differentials. Also aware that a lot of people switched to it without any issues. I guess Amsoil must be making this [censored] up to sell less oil.

 

[Pablo]

Ralph - we are talking seals, not gaskets. If you would have said gaskets in your OP, then I would have said something more.

That said - the fault lies with the cheapie RTV used by American Axle. If you have "b. All 9.5 inch rear axles built before mid-February 1998 (RTV sealant used to seal cover pan)...." then I would simply remove the cover after draining and re-seal it with a good RTV - problem solved.

 

[unDummy]

They also don't specify "which type of synthetic" dissolves or loosens up their cheapie RTV. Unless AA wants to be specific, there is something wrong with THEM.

 

[cronk]

My 93 Chevy p/u has a paper gasket on the rear cover.
I switched over to Valvoline Synthetic 75w140 about a year and a half ago with no issues.

 

[Ralph_S]

That's my bad, thanks for clearing it up.

 

[Pablo]

It's no big thing. I'm most curious what differential you actually have.

 

[cchase]

I drained the diff fluid in my 93 2 years ago with M1 75w90 synthetic after ~360k miles and have not had any problems so far. No guarantees in life but it seems fairly safe.