Vibration, What to do Next


There have been many helpful articles on this problem, but where do you start when all parts look sound and in good condition?
I purchased a 92 400E new, now has 92,000 miles, maintained in excellent condition, and it has a vibration which is felt in the rear of the car. The vibration is felt more at higher speeds (as 67-71;77-81, and at certain speeds you feel little or no vibration. Basic problem solving tried: switched wheels and tires, replaced the rear shocks and front struts, checked wheel bearings & repacked, check alignment, visually inspected all suspension parts, driveshaft-flex disk, etc.
What do I/dealer start replacing, any suggestions as to a starting point, or what order in replacing parts? This can be expensive as you all know, and I'm not sure where to go next. Note posting below. M.B. DOC, is this vibration noticed without applying the brakes? Appreciate your help, Thanks Tim

M.B.DOC
Moderator

Registered: Mar 1999
Location: Snellville, Ga USA
Posts: 3416

As most of the 1992 400E's had rotor problems under warranty, (vibration) the fix was to use calipers & rotors from the 1993 model. Sounds like your car!

Mine is doing the exact same thing. Please post if/when you find out what it is.

urbanassault,

I've been chasing this problem, and from what I have found in all the posts, a vibration can be difficult to diagnose. I'm thinking about changing the lower control arm bushing, have you tried anything?

timreid

I fought my vibration problem for months and with too much $$$ replacing parts after parts.
I also had fairly severe vibrations between 50 and 70MPH.
New tires, tripple balanced, switch wheels, new flex disks, new center bearing, tripple check suspension components, balance drive shaft, etc, etc. . None of it changed anything.
I found a new ''old', specialist who diagnosed weak engine supports. He was so sure of his diagnostic that he told me he would not charge me anything if this would not fix the problem.
A few hours later, the engine mounts were replaced. VIBRATION TOTALLY GONE"
It's been over 70K since then and the car still runs very smooth.
That may be your solution.
JackD

Thanks JackD

As you stated there are so many directions on the road of the unknown cause of a vibration can take us, all which lead to $$$, without correcting the problem. My thoughts was to try the lower control arm bushings since there was a service bulletin issued, and then I did not were to turn to next. After reading your comments, maybe I should flip a coin, but that's why I’m asking for feedback like yours, someone who has walked the walk.
I’m going to let my dealer do the work, and I'll suggest the bushings or motor mounts first. Again thanks for your input, timreid

Have you tried sitting with the car in park slowly increasing the engine rpm's until you feel when you have noticable vibration (on mine around 1400 then again 2200 or so) which translates into around 75-80 on the road. . The vibration might be engine related transfered to the drive train. Bad mounts would allow this big time Also when you are getting the vibration while driving try going to a slightly higher speed then put the transmission in neutral again isolating the suspension from the driveshaft and engine. Might help pinpoint the problem. Good luck. I had a vibration problem by the way in the rear of my car for about 5 months. Did the balancing thing...Did the new Tire thing.. Finally did the new tire thing again (Michelin preformance) and still had vibration. Drivers rear less than 5k miles started to split on the sidewall. Dealer replaced it with a new one and low and behold no vibration so it's sure possible to get a bad brand new tire. Twice even.
Good luck.

Bzoo
I tried the rpm test yesterday evening and at the 2000 rpm there was some roughness, then I did the highway test as you suggested, the vibration did not change. I thought the vibration might change, when I shifted into neutral since there was some vibration at 2000 rpm test, but it had no effect on the vibration. Do you have an opinion of what direction this test would lead me, maybe it’s just suspension related? What Michelin tires did you buy for your 400E, and did you get the air/vent problem solved? The only tire blow-out I ever had was when my wife and I was returning from a Nascar race outside of Atlanta, she was driving our 89 300E, about 85, and a rear Mich x blew its side wall out. Other than the noise, the car tracked straight ahead!
Thanks, timreid

Hey guy I have Michelin XGT-H4's. If the vibration is still there in neutral the arrow points to the wheels / suspension. That has two primary flow chart directions. First question is is the suspension failing to control , maintain, the tire's contact to the road which is a suspension problem or is the tire reacting poorly to the road,, structure problem. If moving the tires around doesn't change the location of the vibration then your looking in the direction of the suspension. I should add here a big culprit in vibration problems is alignment. The tire is constantly bouncing/reacting to irregularities in the road surface.A good alignment and the suspension returns the tire to the road without the action being particularly noticed by the occupants but a bad alignment or worn parts leave the wheel under drag responding with an eliptical bounce instead of vertical and the suspension doesn't control that when it's constant. My pop is a GM tech last 32 years and what I have written above is what he has told me. I have used the theory with luck with my own cars. I hope it helps you diagnose the problem. It's also possible by the way that you have two bad tires.

and thanks for asking about the vent issue. haven't had a chance to try the diagnostic proceedure recomended yet. just can't seem to get a chance to work on my own car..maybe tonight

With your provided help, maybe it is those lower rear bushings that were updated for 92-400E’s, and I’m going to swap wheels/tires again, just to rule them out, before spending $$$.
Thanks