Rear axle backlash

[auret]

I have a 1970 280sl auto with 176,000 miles. There is a clunk in the rear end when changing in and out of gear. It appears to be more on the right side. There is also a clunk in the right rear when it changes from 2nd to 3rd, less so when changing from 3rd to 4th. This is far more noticalbe when driving downhill. I replaced the upper differential mount and it made no difference. There is no noise when the car is going over bumps. The rubber mounts on the trailing arms and springs seem to be fine. With the car jacked up and the wheels off the ground there is slight side to side and up and down movement with stress and you can produce a faint knocking sound on the right - not the left. When you rotate the wheel there is a slight lag before the opposite wheel starts to rotate in the opposite direction. If you change the direction of rotation quickly there is an audible clunk and slight lag before the other wheel starts to turn. The is no howling in the rear end and no noise that would suggest worn bearings.

I would value any thoughts on what the problem is and advice on how to go about repairing it.

Thanks

[Naj ✝︎]

Could be a worn differential housing where the pinion pin fits in it  

naj

[JimVillers]

Aurnet .... It is hard to guess the problem.  My thought is that the U-Joint for the swing axle is the most likely area for a clunk.  Bearings make noise but not a clunk.  I would also inspect the U-Joints in the drive shaft as they might have been turning when you turned the rear wheel.