1985 300sd side to side shake (kind of loping) at idle when warm.
 

Well, I bought the 85 30sd I went to look at 280miles away. I was drooling when I saw the $2600 receipt for a recent "tune up" from a local mechanic which included all new hoses(even transmission cooler), belts, waterpump, and almost complete front end rebuild. The paint sucks, but cant be too choosey...
Anyway, I could tell that the man always babied it and he admitted to never driving over 60-65mph, well the first time I took her to WOT I lost sight of my civic that a friend was following me with on an on ramp. It poured black smoke. After a few rounds of that and 75-80mph driving for 5hrs, she doesnt smoke. BUT, she shakes really bad. And by shake, I mean the whole care moves side to side slowly, almost like extreme loping. Only at idle, and if I pick the idle up to 800-900 it goes away.
After some searches I decided the issue may be worn out engine damper shocks, so I went out to look at them. NEITHER ONE WAS THERE! Completely gone, just empty holes for where they mount. So Im alittle pissed I didnt see this when I was looking at the car, bc now I have to spend another $250+...
Also, am I correct in that a 85 300sd should have a 120mph speedo, bc this one has an 85 like out of an 81-82?? Need to replace that soon, drives me nuts to be doing 65, and looking down and thinking im doing 100mph at first glance.

Rack Damper.....Do a search here for a replacement.

Answer
 

Check the salvage yard for good used engine shocks and upper mount.



so, what does that rack damper bolt (617) actually do?
so, what does that rack damper bolt (617) actually do? - PeachParts Mercedes ShopForum

Part# rack damper pin for 1985 300SD
Part# rack damper pin for 1985 300SD - PeachParts Mercedes ShopForum

Adjusting the Rack Damper Bolt
Adjusting the Rack Damper Bolt

Replacing Rack dampener pin
Replacing Rack dampener pin - PeachParts Mercedes ShopForum



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Replacing the shocks won't do anything for your idle. When the engine is running, they serve no purpose. Since the engine mounts are relatively soft, the shocks keep the engine from tearing them up when it's started and stopped.

As has been suggested, the rack damper is most likely your solution.

Agreed.

Disagree
 

The FSM clearly states they are for idle rock damping.

A bad or failing rack damper pin exacerbates the issue.



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Thanks for all the info guys!! looking into the rack dampener this week. The car only seems to do this side to side shack once it has been completely warmed up. So I was starting to think that it had to be something in addition to the engine shocks, because It wasnt doing it all the time.

Quick question before I dive into new engine shocks this weekend, is it possible to install these without removing or the bolts from the engine mounts? I am at school and tools and jacks and what not are limited, if its going to require removing the engine mounts I may just wait another week or so until I can get it home and use the car lift at home. Any insight would be appreciated. Basically can I do this in the student parking lot with limited tools in my emergency tool kit?:rolleyes:

Mine has no engine shocks, I took them off when I had the engine out a few years ago, makes no difference as I fine tuned the rack damper and idle to the point where it doesn't move at all. Just did it on my dad's SD also which was shaking, calmed it down about 95% with a new bolt and some adjustment.

Adjusting the rack damper is on the agenda this weekend as well (replacement if needed) I was under the assumption that without the engine shocks, that the engine mounts were under more stress at start and shutdown even with a nicely adjusted rack dampener?

You could also have an engine like mine that has new mounts, shocks, and injectors, but intermittently shakes at idle. Im going to put an RD into it, though mine is fairly low mileage and it has the gold bolt... See what happens.

So it could be air in the lines or something else...