85 300D throbs at idle when automatic is in"D"
 

My 85 300D, which is well maintained, shudders and throbs, when I apply the brakes to stop it at a Red Light and the Automatic Transmisson is in "D" position. The shuddering/throbbing seems to come from somewhere in the Exhaust System, believe it or not. Other ideas I am thinking that cause it may be the Pilot Shaft being Loose, Transmission misadjustment, Transmission or Engine mounts...

The shuddreing throbbing goes awy when I place the gear selector in "N" vice "D".

I will put the car on JackStands this week to do a full investigation, but does anyone have any ideas?

Do you feel a pulsation at all when you apply the brakes? I had a similar problem when braking, it only surfaced after I replaced my engine and tranny mounts. It turned out that the rack damper pin was out of adjustment.

What is the Rack damper Pin?
 

Thanks RC. Where do I find it and how do I adjust it? Thank you. When you mention the word Rack, what do you mean?

Thanks RespectfullY RC

Throbbing
 

First thing to check is engine and transmission mounts,make sure they are in good condition.
While you're under the car checking the mounts inspect the exhaust system including the bracket that attaches to the trans.
As always use jack stands and work safe!
M.F.

You can find the rack damper pin at the back of the fuel injection pump. I think you'll need 12mm and 14mm box end wrenches. Do a search and you might get more detailed info. I replaced mine because it was screwed in all the way and could not be adjusted anymore. I really don't know what is meant by rack, I just know that's what the thing is called.

The rack is the final actuator link inside the inj pump. Similar to a rack and pinion. All of the pump barrels are geared to the rack so that through one action all delivery chambers change accordingly by rotation.

The pin acts as a dampener, at idle delivery, against the rack. It keeps engine vibrations from influencing delivery amount and causing an oscillation in engine speed.

Your problem sounds more like mounts as Mike said.