Otherwise you need to replace them and they are $$$. Usually the outer joint gets loose internally and contributes to the clunk. Don't know which side is short 1/2 shaft. In future mark parts when you pull them. Also check the 2 piece driveshaft center support bearing rubber surround and the bearing and the tranny rear isolator that sags with age. The drive shaft universal joints could be worn. They are not replaceable, but some shops can do replacements. Excessive ring and pinion gears lash could also contribute to clunk. Also the rear sub frame bushings and the diffy bushings could be loose and produce clunk. It is usually the added affect of a bunch of things.
