my service manual states the 75 140 synthetic oil in my truck's rear axle is a lifetime synthetic oil and only needs to be changed if it's submerged in water or leaking. does this oil not break down like all other lubricants? the truck is an 01 with 56000 miles and I'm just tryin to swap out all necessary fluids before its too cold out up here.

 

I think most people are changing it out at the 100,000 mile mark if not before.

 

If you have limited slip, you should change it at least every 100k, and use friction modifier. Otherwise, the LS clutches are going to start to chatter.

 

Thanks guys. It is an open diff. I'll wait till I hit 100 and change it out at the same time I do the front just to make sure its good and clean.