It would probably be helpful if you better described the problem. When does it clunk? Every launch? Only hard launches? When driving when you come on/off the power? At regular intervals?
Normally a worn diff will whine. Clunks in a Spider I’d be looking at the driveshaft first: either center support and bearing (even if done at some point in the past) or maybe the splines.
Thanks for your thoughtful reply.
Frankly, after doing considerable research on repair of our differentials, I fear the challenge (including special measuring tools) is beyond my feeble abilities, although complete R&R of the axle is not out of the question.
To answer your question, driveline clunk in my 120k Quad has existed since I bought her @70k and over the years, the problem was attacked through replacement of the center bearing (much improved, since the bearing had been movable by hand), R&R of all universal joints (also were loose), Guibo (cracked and dry), and front diff seal (leaking). R&R of the tranny mount also helped considerably, and I feel foolish for enduring that problem for so long.
Guidance on the driveline forum indicates only 1/4" (or something?) of lash should be felt using fingertips with rear of drive shaft disconnected at diff. Without disconnecting, I have probably 1/2" (!) in each direction.
Clunk presents on each take off and all on/off throttle conditions.
I have come to accept the issue as "character" and franky, unless something breaks during Autocross, feel disinclined to pursue the matter further.
So why am I posting, you may ask?
See my comments on "repair in a bottle".
Again, thanks for your interest.