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  #1  
Old 06-06-2012, 09:18 PM
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'84 300sd Replaced Engine Mounts, still shaky

Hi all,

I had a pretty bad shake at idle. I replaced my engine mounts, one of which was literally in two pieces. When I first started the car with the new mounts, it seemed really smooth. However, I notice now that the car is shaking at idle again- in P, N, D, R, whatever. I tried to change the idle with the rack screw (I have a new one), but I couldn't seem to find a smoother spot with it. Should I change my trans mount? Is there something else I should try first?

Thanks,
Jack
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1984 300SD. 115k miles.
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  #2  
Old 06-06-2012, 09:25 PM
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Location: Bethel VT
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Sure sounds like rack damper bolt, it'll cause a pretty severe shake at idle (and kill mounts quickly) Did you inspect it or attempt to adjust it?

Otherwise, it may be missing at idle due to some air in fuel or dirty injectors?
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  #3  
Old 06-06-2012, 10:07 PM
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I replaced the rack bolt with a new one from peachparts a few months ago. With the engine at idle, I am turning the rack bolt in and out to try to find a spot where it runs smoother. It seems smoothest almost tightened all the way, and when I loosen it more than a few turns, the shaking gets absolutely wild, and the RPMs drop. Now it idles 600-700RPM.
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  #4  
Old 06-06-2012, 10:22 PM
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I certainly would replace the rear mount if it looks as bad as most of them do.Don't you get some relief from that shake in neutral? You should.
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  #5  
Old 06-07-2012, 01:14 AM
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What I had to do to get rid of the my when Engine hot vibration/shaking:

Raise the Idle speed within the normal range (this helped some; it was around 700rpm). I raised it to about 750 rpms.

I bought a new Rack Damper Bolt but it did not help much. I have a turbocharged 300D Tubo and it has a Rack Damper Bolt.

Rebuilt my Injectors with new Nozzles (This took away most of the shaking)

Doing a Valve Adjustment (took away some more shaking). If you can adjust the Valves yourself do that first except for the new Valve Cover gasket is free.

Changed Motor and Transmission mounts (took away some more vibration)

Found that I had a small air leak that showed up when the Engine was hot due to hard fuel inlet lines that did not seal even with the clamps tight.

Finally was able to use the Rack Damper Bolt to tune out a little more shake. (that bolt was made to reduce the shake on a new engine; not to compensate for a bunch of worn and out of spec parts.
Somewhat the same for the Motor and Transmission Mount.

Do the cheap stuff first.

Long Fuel Pressure Relief Valve/Overflow Valve Thread
Fuel pressure relief valve adjustment
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  #6  
Old 06-07-2012, 01:29 AM
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I would try backing off on the idle speed adjustment screw (back side of the IP) before adjusting the rack damper bolt.
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