CAR Rear end fluid change on a y2k GMC

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I've been here a while (like a month), I read allot but do not post too much ......

I've got a 2000 GMC Sierra; I want to change the rear end fluid in it. I bought some Mobil 1 75-90 oil, but I'm not sure if I need to add a 'friction modifier' ... the truck has 4.10 gears with the locking differential. (I've got a 5.0 Mustang with the ford 8.8/clutch pack limited slip and I know it needs the additive, but I'm not sure about the truck)?

Any help would be appreciated …. Also if you do not know, could you post me some good websites for GM trucks … I know a lot of great sites for the ‘Stang, but I do not know of any good truck sites (with good forums).


OT's Master Tech
Nov 21, 2001
Yarmouth Port, MA
I think it depends on the type of locker.. some lockers are totally gearless and are sealed, and use thier own fluid, others have friction related parts tha that the oil could mess up. Go to your local dealer and ask them.


dont do it!
it needs special gm synthetic gear lube! this stuff is like $30-40 a quart + friction additive


Originally posted by OneBDGMC57
dont do it!
it needs special gm synthetic gear lube! this stuff is like $30-40 a quart + friction additive

Thanks!!! How do you know it needs the friction Mod? ... the book (owners manual) does not say it anything about it. I think I'm going to put Mobil 1 Synthetic 75w-90 in it but I was (am) unsure about the friction Mod.

are there any good websites that are dedicated to trucks .... like is to Mustangs?


Check your drivers side door. I know for Fords the gear ratio has a letter code that signifies limited slip. I would assume Chevy does as well. If you can find out what code they use to signify one you would know one way or the other. I know its not much help but hopefully that puts you on track to finding out.

OR....maybe just drive over to a dealer and have them look at it. They should be able to tell ya.
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