I just had my rear diff apart to change the pinion seal and axle seals, after doing so I put new gear oil in (75W140 GL-5) and some friction modifier. While checking the seals for leaks after driving at hiway speed, I noticed that the diff was quite hot, almost too hot to hold my hand on. I had never noticed what temp it ran at before but found that the front diff was stone cold (though I hadnt used 4x4 at all) Is it normal to be this hot? Should I stop worrying? I might be a bit paranoid considering I just put that axle in after blowing my last diff...

 

Is the rear end making any noise, a whine or moan while under acceleration? If it is, then the pinion bearing preload was probably not reset when the pinion drive flange was reinstalled after the seal installation.

Anytime the pinion shaft nut is backed off and removed to make a repair a new crushable spacer must be installed and the pinion bearing preload readjusted; otherwise, the pinion/ring gear mesh will not be correct and might cause noise, wear and overheating.
By the same token, if the preload has been set too high, the gear set may be quiet, but the overloaded pinion bearings may generate a lot of heat.

 

That is normal....the housing should be fairly hot to the touch after a decent drive.

 

Thats what ive been hearing from a lot of people I ask, I did set the preload the same as it was previously but did not repalce the spacer. It doesnt make any nosie, I just didn't realize they ran that hot. Should be fine but i'll keep an eye on it, thanx for the advice

 

After reading this thread I made it a point to climb under my truck after about an hour long drive at highway speed and feel the diff. Mine was pretty cool. Cool enough to keep my hand on it without any discomfort. IMO, I would have your diff checked to be safe. Last thing you want is for that thing to lock up on you on the road.