I recently finished my first rebuild and regearing of an 8.8 to 4.10s and just came back from my first test run. Ran it for about 15 minutes and got up to 50 mph. The diff housing seemed fairly hot but I'm not sure how much is too much. Is 5 seconds with my hand on it seem excessive?
Also it seems that I have a whine. Is there a sound it makes while the gears break in?

I had the recommended .012 thou back lash the Ford service manual wanted on the ring gear and the 21 in. ib. on the pinion bearing preload. I used a crush sleeve eliminator and had the right amount of shims there. I rebuild the limited slip while I was in there as well. The pattern looked really good to me and a few people I ran it by said the same.

Thoughts?

 

If it was Open diff I'd say something was off. If it continues to whine I would do some investigating on forums and on the truck for anything odd. I play allot of games with junk but wondering if or when the rear will lock solid and roll you is a game no one sane or likewise should play.

 

Whine is not really normal. The diff getting hot is normal, but you should be able to keep your hand on it, especially if you were just driving around normally.

I'd take the cover off and double check your pre-load, gear pattern, and make sure the main carrier bearings are torqued correctly.

 

Well I may have posted this in haste. I just took it for another test run (both runs being under 10 miles each) and the whining has stopped and the temperature is only warm. I could keep my hand on it indefinitely.

I had talked to quite a few people today about this issue and at least half had mentioned it may be the way the gears were cut. Some gears make more noise initially until they break in. I guess I'll chalk it up to that for now. Obviously I'll keep an ear out for the first 100 miles (just under 20 miles at the moment) and then change the fluid.

 

Brand new gears will get hot and whine a bit at first, some brands worse then others, this is why break ins are in short runs with plenty of cool down time and no working load or trailers for at least 500 miles!

-Enjoy
fh : )_~