In two of my Benzs ( an '84 500sel and an '84 500sec ) there is a loud clunk when decelerating. The noise just started in my sec. It only happens during medium braking and when the transmission shifts from second into first. It sounds like it is coming from the differential or one of the axles or even the rear of the transmission. The mechanic ( of course ) is having a hard time replicating the problem. It only happens during a specific degree of braking, any harder or lighter and there is no clunk. Any suggestions would be greatly appreciated.

I would think that from description that the noise is comming from transmission. There must be a very high vacuum to trans durning decel or it will have harsh downshifts. Possibly the modulator is starting to go bad(vacuum leak).

Thank you,
I will check it out this week!