Fluids Change

[Dean Barker]

In preparation for the fluids change in the rear axle and 6 speed transmission in my 1996 LT4, I poured over all the service books for the wrench sizes for the trans drain and fill plug and the rear axle fill plug. Couldn't find the information anywhere, so took it for a 20 mile drive to mix things up, put it up on jack stands, and took a look. The "special tool" that the 101 Corvette projects book called for was simply a 3/8 allen wrench. The transmission drain and fill plugs required a 17 mm allen wrench which I borrowed from the local Chevy dealer. I replaced the the trans oil with the GM 5W-30 transmission oil. I sucked out the rear axle fluid thru the fill hole and replaced it with Mobil 1 75W-90 synthetic gear lube with a bottle of GM limited slip additive. Would have been nice to have had the proper wrenches on hand before starting. Am going to look into the drain plug kit for the rear axle from Corvette Clinic in Florida.

 

[boomer]

Are you changing them b/c of miles or another reason? Also, how bad was the changing process? Doesn't sounds all that difficult.....
Thanks,
Oliver

 

[Dean Barker]

The car has 33,000 miles so a change was probably not needed. Any vehicle that I buy, new or used, I always change the fluids to flush out any machine chips, etc and that way I know what is in everything.

I bought the suction gun from NAPA, and used it to suck the old fluid from the rear axle. I cleaned it up and used it to fill both the rear axle and the transmission. It worked good; not hard at all. The reason I went with the Mobil 1 synthetic gear lube for the rear axle was GM seems to be screwed up lately on their gear lube. They installed lube in the front axle of 4X4 pickups that caused the units to fail. They replaced thousands of front axles in new pickups. This is according to the local Chevrolet service manager. He said all the local Chevy dealerships were using the Mobil 1 instead of the GM recommended fluid, because of quality and price. I did buy the GM positraction additive. Hope I answered your questions. Dean Barker

 

[boomer]

It does, thank you Now I know what I'm doing next weekend... :L

Oliver

 

[Hib Halverson]

GM, via the factory service manual, specifies no interval for rear axle lubricant service but...that's based on GM durability targets which, in turn, are based partially on the idea that GM wants you to buy a new car or at least buy rear axle parts.

You can significantly extend the life of a Corvette rear axle by changing the lubricant every 3 years or 36,000 miles whichever comes first. Mobil 1 axle lube and the GM limited slip additive (only if needed to eliminate limited slip chatter or squeal) are good choices.

The tool needed to remove the plugs on the ZF S6-40 six-speed is very common. Go to any parts house selling foreign car parts and buy a Volkswagen transaxle too. It's a 17mm hex bit which fits a 3/8-drive rachet.

When installing a "drain plug kit" make absolutely sure no metal chips are left inside the axle after the drilling is done.

 

[Dean Barker]

I should add a comment on how the old fluids looked to me. The old transmission fluid looked ok, clean, clear, and new looking. However, the rear axle fluid looked like black, thin diesel fuel. Maybe not quite as thin as diesel fuel, but it didn't look too good. I was glad to get it out of there. I checked with Corvette Clinic on the rear axle drain kit; $55.00 plus shipping. I thot it was kinda high so am going to find a Corvette friend to share the cost. I'll be ready for the next change. I'll be careful with the chips; the fluid coming out will bring the chips? We just got home from a 1800 mile ride in the Corvette; what a ride!!!! My ecomomy car; 27 plus mpg!!!