Rear diff. not locking in!

[Rhoward225]

Normally I have no problem in the mud w/ my 4X4, but I have gotten myself stuck twice this week. Come to find out the reason why is my rear end is not locking in as normal. I have never had a problem in 327,000 miles w/ plenty of off road time. All fluids are checked and changed on regular basis. Can anyone suggest what might be going on? Thanks,

[More Power]

After 327K miles, the clutch discs in the locking diff may be worn enough to not provide a lockup. New clutch discs can be installed. :)

Jim

[Rhoward225]

Thanks Jim, is this something easily replaced? I've never pulled the rear cover to get a good look at the internal make up. I use Lucas gear oil in both my diff. and the fluid still looks pretty good. Could I need to try and change out the fluid and clean it all up. Or more than likely the disc are just work out? Thanks,

[More Power]

The G80 locking rear diff I have experience with is not easy to work on. A drivetrain mechanic friend and I took a AAM-950 GM corporate rear G80 apart a few years ago to replace the spider and axle-end gears. It was a pain. While in there, I saw the clutch discs, and they would have been easy to replace - once you get it apart.

The following image of an AAM-1150 rear diff was taken at Randy's Ring & Pinionin Everett, WA. It was removed from a GMC 2500HD. Not sure if this is a locking G80 or not.

http://www.thedieselpageforums.com/photopost/data/500/2500hdrear01.jpg

Jim