GM 14-bolt FF Rear End with 149k miles
Hi to all, Our TV is a GMT400 1997 GMC K2500 7.4L Burb with 149k miles. It is 8-lug, 3.73, GVWR 8,600, with GAWR RR of 6,000 lbs for the full floater rear axle. We believe the rear end also has 149...
Forum Discussion
MartyW wrote:
They were happy to do a differential service but they would not add synthetic fluid. They said the synthetic fluid would cause the sealer to leak as the stock setup has no gasket.
No gasket, as in the cover is sealed with a bead of RTV, that must be removed and replaced at every fluid change. It is true that synthetic fluid will attack some types of RTV sealer and cause a leak. BUT there are types of RTV or sealer that are NOT affected by synthetic fluid. There have to be because synthetic fluid was installed from the factory.
From my Owner's Manual:
Rear Axle Lubricant: SAE 75W-90 Synthetic Axle Lubricant (GM Part No. 12378261) or equivalent meeting GM Specification 9986115.
The only thing the Lube-Lock gasket does is save you from the mess of having to scrape the old RTV off and re-RTV at every fluid change.
Not sure if things were different for your year truck, but the axle is the same, and there's no reason not to use synthetic.
Of course, I also run Mobil 1 oil in the big block...
I wouldn't sweat it too much though. Since you have fresh fluid in there, run it for a season and see how it does. You can always add synthetic at the next fluid change. You might want to ask the dealer about the P/N referenced in my owner's manual and see what they say.
On edit: the 1997 owners manual says:
Differential, Front and Rear Axle: Axle Lubricant (GM Part # 1052271) or SAE 80W90 GL-5 Gear Lubricant.
Bear in mind that the neither manual distinguishes between the 1500 and 2500 series trucks, so that means the half tons got the same lube, either regular in 1997 or synthetic in 2001.
