I have 1985 300D auto trans. I hear a clunk sound when I shift into neutral on my way to drive. I also notice from the rear of the car that if I tap the pedal during neutral or park (if the parking pin isn't engaged yet) the driveshaft rotates clockwise and lightly bangs against the inside of the diff. I have clunk noises everytime i downshift. I replaced trans mount, carrier, and diff mount. I hear a clunk sound on the highway when i let off and on the pedal too...

Car has 145k on it.

Sounds to me like a CV Joint, on one of the axles, with a lot of wear. The most obvious is the boot is cracked and slinging oil. However, mine didn't have that symptom initially. When I had it in the air, on jackstands, one of the CV Joints had an odd angle.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

This is possible.. I'll look into it. Since i got this car a year ago I have changed front shocks, both flexdiscs, trans mount, carrier mount & bearing, diff mount, both rear axles, and diff fluid. subframe bushings and rear shocks are next on my list.

It is very possible that your driveshaft u-joints are either frozen, or bad altogether. Mine was clunking similar to what you describe, and when I changed the driveshaft center bearing, I soaked the u joint with rust penetrant, and then a lot of penetrating oil/grease and freed it up. Now, no more clunks and muuuch smoother on the highway. Just my .02

__________________
2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

Just an idea the micro switch on your throttle quadrant might be shot check to see if it clicks as you push on the arm .