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RE: Vibration at 50mph

schneller — Wed, 02 Apr 2008 09:33:54 GMT

The 55 mph shimmy on that chassis in my experience is attributed to the thrust arm bushings.

If you're interested in the mechanical details this is how it happens....Typically, one bushing is weaker than the other. Since the thrust arms position the wheels front to back, they also take the brunt of all braking loads which are absorbed by the thrust arm bushings. When one bushing gets weak, it allows that thrust arm, even while not braking, to drift rearwards. When this happens the suspension pulls that tie rod along w/ it, the steering wheel turns & then the suspension on the other side pulls the whole mess back to center & the oscillation starts all over again producing your shimmy, which seems to show up best in the 45-55mph range.

There are 3 reasons for weak bushings: 1) age. 2) Improperly installed..these bushings need to be preloaded evenly after install, else your new 750il or e34 M5 bushings will shimmy too!. 3) Cheap after market bushings will fail quite soon...you get what you pay for.

I hope this info steers your mechanic in a direction that will solve your shimmy.:)

Mike Morris
Schneller BMW Performance
26 Middle Rd
Newbury, MA 01951
978.465.2002

RE: Vibration at 50mph

danarussian — Mon, 31 Mar 2008 18:35:46 GMT

If you have 17" wheels on stock upper control arm bushings you are likely to have shimmy, even if the bushings are new. For heavy wheels and tires, you need either poly bushings or what I use, milled 750i bushings. Meyle also now makes a HD bushing, but I do not have personal experience with them.

RE: Vibration at 50mph

00BMW540i6 — Mon, 31 Mar 2008 16:08:02 GMT

This is typically due to a thrust arm bushing on E39's as well.

RE: Vibration at 50mph

KenM10759 — Mon, 31 Mar 2008 11:52:52 GMT

Pardon me for jumping in Mike -

Do you get it more on acceleration or deceleration? On my '88 E28 (similar if not identical front suspension setup) I got it on decel at the 50-45 zone. It was corrected by installing new thrust arms.

Yours sounds more like wheel bearing or balancing issues. Have you had the tire/wheels raod force balanced? The Hunter GSP9700 balancing machine applies force to the tire as it rotates in the machine, giving a more accurate reading because it'll take tire out-of-round conditions into consideration. If you Google for Hunter's site, they have a search function that will find shops in your area that have the GSP9700 (or other models that may now be out there with the feature.)

Vibration at 50mph

85_635csi — Mon, 31 Mar 2008 08:48:00 GMT

Have replaced the front end almost completely but havent touched the steering. When driving I get an intermittent strong vibration in the steering wheel at 50 -55 mph. You can drive through it and doesn't happen all the time. The car has 17" tires on aftermarket wheels. Have tried the balancing and front end alignment but it still is present. I have been told that 1) the wheels are too much for the 1985 front end and 2) that the spline in the steering is worn (and was tightened) Any ideas?