Gear oil in a g80

[Piratehunter]

just my preferences, when I replaced the oils in my '97 K2500 nv4500, g80, and transfer case, I used the GM/ACD recommended numbers. Some were more costly and harder to find, but I had time to get them. paid a bit more, but that was my preference to stick with factory spec ACDelco fluids. When I drained them all at 120K miles, they didn't have metal or look contaminated, so I figured if they've held up good for 120K, I'll stick with them. at the end of the day, I'm sure that most brands that are of the same spec will work just as well.

 

[boy&hisdogs]

I learned this one the hard way, you need plain oil, NO FRICTION MODIFIER!

The shop that did my gears put friction modifier in it without asking and surprise surprise, the G80 didn't work when I needed it to and I had to get a friend to pull me out.

 

[Schurkey]

I bought Valvoline gear lube for my K1500 with G80. Back of the bottle says it's for "top-off only" on limited-slip differentials. Which means that it doesn't have friction modifier blended-in.

Saw a similar product at O'Reillys--for top-off only on limited-slip differentials. May have been the O'Reilly's house-brand.

GM also has a bulletin on synthetic gear lubes, and how they're not to be used on axles that have RTV Silicone sealer. They claim that the synthetic lube will degrade the RTV Silicone. There's model-year breaks for axles produced with and without the silicone sealer; and retrofit part numbers for converting older, silicone-equipped axles to mechanical gaskets. If you still have RTV Silicone sealing your axle assembly, you shouldn't use synthetic gear lube.

Sounds fishy to me. Guys have been using RTV Silicone on differential housings since Fido was a pup. UNPROVEN SUSPICION: AAM who made the axles, used the cheapest, crappiest RTV Silicone on Earth; and that one silicone product failed when tested with the one synthetic gear lube they used--which is probably also the cheapest, crappiest synthetic gear lube on Earth.

But what do I know?

 

[Orpedcrow]

Just to add, Make sure it’s a GL5 rated oil.

 

[Rocket Surgeon]

GM also has a bulletin on synthetic gear lubes, and how they're not to be used on axles that have RTV Silicone sealer. They claim that the synthetic lube will degrade the RTV Silicone. There's model-year breaks for axles produced with and without the silicone sealer; and retrofit part numbers for converting older, silicone-equipped axles to mechanical gaskets. If you still have RTV Silicone sealing your axle assembly, you shouldn't use synthetic gear lube.

Bizarre.

Is the only RTV on the case cover???

also, last few times I have done anything related... I used Permatex Moto-seal. It is not an RTV product and is designed to strongly resist oil....

 

[454cid]

I always use paper gaskets. My 14bff had one originally, and I've used a factory gasket each time I've gotten in there. Even if it were a crappier than normal rtv it's not like its reusable, nor would the gear oill be the same.

Last time I did my rear axle I found a oem kit on ebay.....bolts, gasket, and cover. I think it was surplus, as I didnt pay alot.

 

[Schurkey]

The differential cover gasket/sealer, and on the full-float axle, the axle shaft-to-hub seal.

 

[Erik the Awful]

GM ... claim that the synthetic lube will degrade the RTV Silicone...

Sounds fishy to me.

Yup. Wouldn't modern gasketless engines start spewing synthetic oil out of their RTV seals?

 

[someotherguy]

I've read that warning on oil manufacturer's websites, so it's not just GM that makes the claim.

I suspect it's probably "old" information that came when synthetic lubes were new to the general market, and RTV formulations may have changed by then. It's probably still relevant info for vehicles that were made back then and haven't yet had those seals broken and renewed, which are going to be in the minority at this point.

All of the above except the first sentence would be WAG's, of course.

Richard

 

[Schurkey]

Yup. Wouldn't modern gasketless engines start spewing synthetic oil out of their RTV seals?

Engine oil and gear lube are different products with different additive packages.

In addition, the axles were not made by GM, they're made by AAM. No idea where AAM sourced their lube or their RTV Silicone. AAM also supplies axles to "Ram", so it'd be no surprise to find Dodgy bulletins on the same subject.

The crucial bulletin info:
The TSB is Bulletin No.: 99-04-20-001 Date: June, 1999

The specific car Models:
1999 Cadillac Escalade
1988-99 Chevrolet and GMC C/K, G Van and P1-3 Series Models Built before the VIN Breakpoints (C/K) listed in the TSB (mid 1998).

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.