On the '87, I've got a high frequency rhythmic vibration that's slowly gotten worse over time. Sort of a "droning" or "thrumming" that others have mentioned in other posts. Starts being noticeable around 55-60 mph, eases up around 70, and comes on strong around 80-85 mph. I can feel it in the seat of my pants, through the accelerator, against the door, and through the gear shifter. Have finally decided it's bad enough that it will be the next repair item, once my credit card recovers from a new set of tires and front end work on the '91.

-Suspect engine, which has a slight stumble at idle, and a much lighter version of vibration when revved in neutral to 3000 or so.
-Motor mounts changed a few months ago, helped a little, but not for very long.
-Rotating/balancing/new tires made no difference.
-Center bearing support changed (for a different vibration, which went away, then came back... fun!) a couple of months ago, no difference.
-Vibration worses when accelerating, lightens up as I ease up on the gas pedal. As speed falls away, the vibration goes from high frequency to low frequency, then disappears eventually.

Looking for a place to start..

thanks,
anthony

When troubleshooting a vibration, you must first determine if it follows the speed of the engine, the speed of the car, or maybe the speed of the driveshaft.

If it is the engine, you will probably have it when you reve the engine in neutral.

If it is driveshaft related it will be very high frequency, about three times as fast as if it were a wheel. Either one of these will be proportional with vehicle speed regardless of what gear you are in.

BTW, a ridiculously high percentage of vibration complaints turn out to be wheel/tire related. Just because they've been balanced does not mean they are not the culprit. First of all many tire stores won't balance Benz wheels correctly because they insist on static balancing with weights only in the inboard lip for cosmetic reasons. You will rarely eliminate vibration this way.

Secondly, tires can have stiff spots. The only way to determine this is by having them run on a Hunter GSP9700 machine. You can find the location of one in your area by going to: www.gsp9700.com.

Good luck,

did this show up after the driveshaft was monkied with? if so, try splitting it and rotating it 180 degress at the joint.


Joe

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Acme Automotive Inc.
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Just wanted to follow up.. Turned out it was the driveshaft. Apparently the "Inner drive line bushings" were binding, and preventing the joint from rotating freely. Had the shaft R/R'd and sent to a local driveline shop, which replaced those. That plus the front flex disc has more or less taken care of the vibration.

-anthony