Maybe this will be of help to someone with the same problem. A little back story. My car (auto) clunks when shifting from 1st to 2nd and sometimes 2nd to 3rd. Also if you give it gas, let off, then give it gas again it clunks bad. I have replaced LCA's, panhard bar, posi, ring/pinion, u-joints, and tranny mount trying to find out where it's coming from.

Well after a year or two of putting up with this problem I decided to jack up the rear today and try to find out what was clunking. I recently got a good floor jack so I put it under the rear diff and lifted both rear wheels off the ground. While turning the driver side wheel back and forth with my feet I found the slop in the drivetrain. It's coming from either the output shaft of the tranny or the front of the drive shaft. I'm thinking the splines are worn.

I don't have the time today to take off the driveshaft so my question is what is more likely to wear out the outputshaft splines or the front of the
driveshaft?

 

If the sunshell & the reverse/input drum have too much clearance between them, then this can happen, a clunk. This will be ok in most cases, just annoying till you have the unit rebuilt, at which time the sunshell is most likely to be replaced, and the reverse/input drum checked for excessive clearance with the sunshell.