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Steering Shimmy while Braking at Full Chock

1K views 3 replies 3 participants last post by  Mango 
#1 ·
Hi all,

Car is a 04 330ci that recently had the rack and rims replaced after hitting a pothole.

At or near full chock, like when pulling into a parking space, if I am coming to a spot a bit quickly and brake, I feel a shudder as if ABS kicks in. I am definitely not seeing an ABS light and it happens for such a short amount of time, it is difficult to diagnose. Also, this doesn't seem to happen at higher speeds. I only know this because I took a trip to Palomar recently and went through a few REALLY tight corners at full chock (stupidly with some braking).

I am just wondering if anyone else has noticed something similar or has any idea what this could be. The rack was installed at BMW, so I assume that they bled that system properly. I am thinking that maybe there could be some air in the brake lines? Could that cause something like this? Is it the FCABS or some other bushing?
 
#2 ·
If it's only there when you brake, then it has something to do with brakes, does it feel squishy or spongy when you brake??

Good thing to do, prop up your front end, take wheels off, disassemble calipers and clean up your rotors, calipers and inner wheel mounting. Make sure all mounting areas are nice and flush, the smallest deposit of dirt or paint can give shudder. Clean calipers thoroughly using a wire brush and Brake Cleaner, (I used a Bench grinder with buff attachment). Check for excessive pad wear, spin the rotors with the wheel off after everything has been cleaned up. Reassemble and try again.
 
#4 ·
While cleaning everything up is a good idea, it likely isn't your issue. The #1 culprit would be worn control arm bushings. This would allow your wheel to jerk as you apply the brake. The jerk would only be initial and would jerk again as you brake again. Another possibility is your control arm balljoints (for all intents and purposes, the control arms) which usually fail around 100k miles due to the nylon inserts used with the balljoints (ZHPs and M3s see less failures due to all-metal balljoints)

The last but least likely is pad deposits on your rotors. I say least likely because in my experience and opinion, BMW brakes are large enough to dissipate heat adequately enough as to not cause pads to heat up to the point where they sear onto the rotor. Of course, heavy use with OE pads and fluid can cause overheating but you'd also need to stand on the brakes while at a stop light. It's possible, but unlikely.

You could jack up your car and jiggle your wheel and see if you hear any noises and/or clunks. This method would only show severe balljoint or fcab failure and likely any force you're able to exert with your hands wouldn't be enough to reveal any slight issues with your balljoints or control arm bushings. It's a safe bet that if you have 100k on either, you should be replacing them anyway. Good luck!
 
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