Shaking around 55 mph

My car seems to shake a lot at 55 MPH. I can't tell if it's the motor, like the mounts or, the front end. It only seems to happen at that speed and none other though...ANy ideas? how would I check the motor mounts?

[TonyFromWestOz]

Hold the transmission in 3rd gear, run the car until the engine RPM is the same as when you are doing 55 in "D".
Do you get any vibration?
If not, it is unlikely to be the engine, mounts or shocks.
When doing 55, slip the transmission into "N" and let the engine idle. Does the vibration stop? No? Then it is not the engine.

Check the front suspension, wheel balance (any weights fallen off?), flex discs and drive shaft.

As above. Try switching front tires and see if problem changes.

[P.E.Haiges]

greasy,

I'm betting its one of the front tires. To find which one is causing the shake, replace the front tires one at a time with the spare tire and see if the shake goes away. If the tire isn't too bad, you may be able to use it on the rear or keep it on the spare.

P E H

[lietuviai]

Any one know if new motor mounts would smooth out the vibration from the motor felt at idle.
I'd figure I'd ask here instead of starting a new thread.

Unfortunately my tachometer doesn't work, so I can't test that way. It seemed to start after I removed the tires for my brake job, but maybe I just never noticed it before that. I'll try the tire swap and see if that helps. Can I visually tell if my motor mounts are shot? I'm going to have the oil cooler lines done, so that seems an ideal time to swap the mounts.

[Tirebiter]

Steering stabilizer. Cheap part, easy to replace.

still shakes if i go neutral at 55 mph. So that means not the mounts but tires? How can I tell which one? I actually think this began when I filled my tires with air, could this have caused it somehow?

[P.E.Haiges]

greasy,

Are you dense? I told you to replace the tires one at a time to fine which one is bad.

P E H

[Wes Bender]

Greasy, you're not dense. Probably an oversight on your part, but P E H is right about the front tires being the culprit.

I've found that, when something suddenly changes for the worse, nine times out of ten the most recent work caused the problem. Not always the case, but often enough that I start my troubleshooting there.

Let us know what you find.

Cheers,
Wes

[SoyDriver Matt]

If the mating surface between the wheel and the rotor is a little rusted up, the can cause the wheel to be off just enough to vibrate...at

[TomJ]

Originally posted by lietuviai
Any one know if new motor mounts would smooth out the vibration from the motor felt at idle.
I'd figure I'd ask here instead of starting a new thread.

Try adjusting the rack damper (or whatever PEH wants to call the rack damper bolt)

If that doesn't work, then engine mounts and shocks should do the trick.

[lietuviai]

Originally posted by TomJ
Try adjusting the rack damper (or whatever PEH wants to call the rack damper bolt)

If that doesn't work, then engine mounts and shocks should do the trick.

Thanks Tom, I'll try adjusting the rack damper and then I'll look into the mounts.

[P.E.Haiges]

Wes,

I have found the same thing to be true, if something changes, always look at the last thing that you did that could possibly have caused the change.

TomJ,

FYI: I call it a rack damper bolt.

P E H

[joshhol]

Is there a rack damper bolt or anything on a 115 300D to smooth idle? Valve clearances, mounts and filters and all else being in spec.