i had the same question so i studied the dark art and now i can build very smooth diffs.
Firstly i watched these videos
http://www.youtube.com/watch?v=IIYPo...eature=related
(He mentions it once briefly but you need to tighten your slipper clutch when you breaking in the diff)
The slipper clutch needs to slip before the diff.
The problem with the above method is the way he sets the diffs before first drive, i found the diffs to still slip. this way that Rich D mentions is the best, this will ensure there is zero slip before you go for a drive.
''To set the diffs, this is my method.......
Car facing away from you, hold left rear wheel with left hand. Hold spur gear with left thumb. Turn right rear wheel forward slowly at first still holding the left rear wheel and jamming the spur. You should see the slipper plates turning. If they arent then either your diff is too slack or your slipper is set too tight.
Its a balance that you`ll get a feel for. When its set right, then the diff action should be smooth but it shouldnt slip when you test it on the bench.
For the front, just face the car nose towards you and repeat the method above. I try turning the right wheel slowly at first until im happy that it`s not slipping. Once its somewhere near, i turn it more quickly, kind of "jerk" - this is more like the motor would turn the transmission. If you hear it slip, just tighten it 1/8 of a turn further.''
The slipper clutch setting is just as important as the diff setting. If the slipper is too tight then the diff will slip no matter.
for 2wd just hold the back wheels and try rotate the spur, if the slipper nut moves then its too loose, if its unable to be turned then its too tight, you want to be able to turn the spur without the slipper nut moving.
whenever i rebuild a diff now i always rebuild my slipper aswell.
hope that helps
