My dif. In my stock s80 hydro transmission blew up at the track and I ordered an OBX lsd dif for it and syncrotech carbon syncros 1st-5th. I bought a back up s80 trans and put everything in that one because of all the metal in the other one. Had both lsd and syncros installed threw a reliable shop ( I hope) and from what I have heard and read you normally have to do some shimming but in this case they didnt need to and the differential actually sits about 4mm higher. They said nothing was touching and put the case back on with no problem. Then they tested the gear shifting. All gears shift fine, but said it was a little stiffer/tighter when changing gears. Is this normal or am I missing something? Any info would be great because i dont want to put all this money into and time for something to be wrong and have to take it back out or damage anything. Ideas?

 

The diff sitting 4mm higher is not functionally possible... so either that value is incorrect or misunderstood OR you will have problems with the transmission... likely a failure. A proper diff installation will not affect the shifting feel of the transmission, however, the carbon synchros will likely firm up the shifts, at least for a while during the period of time that the carbon coating wears in.

 

x2

0.04mm is enough to alter some things in a trans. 0.4mm is enough to cause catastrophic failure almost immediately. 4mm is, well, as JRCivic1 said, impossible.
Shifting an un-spun freshly built trans is always going to be stiffer on the bench, with or without fluid. It will smooth out almost immediately after driving it for a bit. Unless the engagement teeth on the gears and sleeves are worn. In which case those should have been replaced

 

4mm is impossible, I'd verify that number with them. Reputable transmission shops don't install OBX LSD's.

 

How much taller is the differential assembly if you accidentally install GSR roller bearings in place of the LS roller bearings ??? Could that be the 4mm the OP discussed ??? I know this won't allow the case to properly snug up... and God forbid you install this transmission in car and put it in gear and let the clutch out... this leads to blowing the side of the transmission case out. Don't ask me how I know... LOL.