Kelly:

It could be the front flex disk. It mated the transmission to the drive shaft. If it si worn, it gets loose and then the clunk.

I head these disks run between 80 to 100 kmi.

Saw your 82 SD for sale. I am in Big Rapids, MI and am interested. Cold you email me to give me more information? You can click on the email button near the top of the message.

Thanks.

Bo