Rebuilding Rear Diff in 94 F-350 question

Iv rebuilt the rear diff in my 94 f350, but seem to have tore it all up again just a week later, i have heard people say your supposed to shim your dif but dont seem to see how that is possible as there are only two 1/4 inch thick washers that go on each side of the diff and the whole thing goes in only one way and sits in a really tight space, i never changed the pinion gear(the one that attaches to the drive shaft) or its bearings and wondering if that is what caused it to fail.

well i rebuilt it again with spare parts, cept pinion gear is finished and wondering if i get new one if this will be a problem as they might be worn differently?

"i have heard people say your supposed to shim your dif but dont seem to see how that is possible "

I know very little about it, but AFAIK, you shim to correct end play of pinion gear. if you are not checking end play and shimming to specs as necessary, your differential will fail again.

Certainly it is admirable taht you want to learn how to do this kind of repair. Still and all, you want to get someone who knows what they are doing to do this kind of work or to watch closely over your shoulder, otherwise major repairs might fail in just a week.

You shim the gears to get the correct backlash between the ring gear and the pinion. The ring gear and pinion gear must be a matching set. The way you adjust the backlash is to purchase different size "washers" for the sides. I believe the backlash range is from .008 to .015 inches. There are approximately 35 different size washers. To set it up properly takes patience and practice. I have not really seen anyone set one up properly the first time they try to do it. It also takes a ceretain "feel" for the set up. There are no shortcuts. As the other poster said, have someone that is experienced watch or tutur you on the repair. Good luck