Front End Vibration

A couple of weeks ago i noticed a slight vibration in the front in at certain speeds. I had the wheels rotated and rebalanced that did not solve the problem my mechanic noticed that i have some burn marks on the front driver side brake rotor. The car shakes rather violent and then it is gone but it only reacts at speeds of 45 to 55 mph. It isn't even a consistant thing it comes and goes and hits at different times and varys in strength if any one can give a thought or has had the problem before any advice would be of some help:banghead::banghead::banghead:

You do not give us year and model, however, the upper control arm bushings (thrust) are notorious for wearing out around 70,000 miles and the condition you describe fits with those bushings being toast.

As bear said, upper control arms (also called thrust arms) are one factor. Tie rod ends can also cause it, and lower control arms can cause it too. Upper strut mounts both front and rear, rear dog bones, rear subframe mounts can cause it. This shimmy is feedbacked through the steering wheel. Unless you have vibration not felt through the steering wheel, then you may have a warped rotor.

We just had this very same problem with a customer's 2001 740il last week.

While bushings may be the problem, the clue here is the burn marks on the rotor. This indicates the rotor has overheated, which can only be caused by contact with the pads. So this tells me that you probably have a sticking caliper or bad flexible brake hose to that side.

Get the caliper off the rotor and try to compress the pistons. If they won't compress, try cracking the bleeder. If the caliper will compress after cracking the bleeder, it's probably the hose. If it won't compress upon cracking the bleeder, the caliper is stuck and you'll have to replace the caliper.

These calipers are hard to find aftermarket if you don't want to pay for new ones from a dealer. I found a pair at autopartswarehouse.com

http://www.autohausaz.com also have some good deals on parts. I live in Canada and they are still the cheapest by far!