Steering wheel jerk on light brake. Sticky Caliper?

[GreatFrog]

Hi guys, just bought a 2003 ZHP with only 34k miles on it. Everything is working beautifully except that the steering wheel jerks slightly when tapping the brake (light braking only, heavy braking does not produce the jerk). The mechanic inspection showed front control arm ball joints are in great shape. I just replaced front control arm bushings myself and it didn't cure the problem.

I jacked up the car at front and spun both the front wheels. The right front wheel spun completely freely. While I could feel some resistance rotating the left front wheel. I could hear periodic grinding noise from brake pad coming into contact with the rotor while the wheel spun, and it came to a completely stop after 2~3 revolutions. I took videos of both wheel spinning:

Front right wheel spinning freely

https://www.youtube.com/watch?v=CZMXN_XNpsg

Front left wheel got some resistance

https://www.youtube.com/watch?v=hOy5gkpEGbk

The video was taken after doing a brake fluid flush at all four wheels. It seems that the previous owner hasn't changed brake fluid for years.

My question is, judging from the video, do I have a sticky caliper? I would expect there might be some tolerance for pads coming into contact with the rotor, just not sure whether my case is in the normal range. Could this be the culprit for my steering wheel jerk at light braking?

Thanks very much!

[BMWCurves]

I have an ever so slight back and forth shimmy in the steering wheel under the same conditions (car still tracks straight under braking), but haven't tried spinning the wheels to see if one has more resistance than the other. It started after I did the brake fluid flush as well. I'd be interested in hearing if other people's suggestions beyond warped rotors.

[GreatFrog]

Mine actually had the problem before the brake fluid flush. After changing the bushing and brake fluid the situation seemed improved, the shake at heavy braking was gone. But still jerks at light braking.

[slater]

hmmm. i had that issue when i first bought my ZHP and it was the FCABs.

what FCABs did you install?

peter

[TheFinanceGuy]

Hi guys, just bought a 2003 ZHP with only 34k miles on it. Everything is working beautifully except that the steering wheel jerks slightly when tapping the brake (light braking only, heavy braking does not produce the jerk). The mechanic inspection showed front control arm ball joints are in great shape. I just replaced front control arm bushings myself and it didn't cure the problem.

I jacked up the car at front and spun both the front wheels. The right front wheel spun completely freely. While I could feel some resistance rotating the left front wheel. I could hear periodic grinding noise from brake pad coming into contact with the rotor while the wheel spun, and it came to a completely stop after 2~3 revolutions. I took videos of both wheel spinning:

Front right wheel spinning freely

https://www.youtube.com/watch?v=CZMXN_XNpsg

Front left wheel got some resistance

https://www.youtube.com/watch?v=hOy5gkpEGbk

The video was taken after doing a brake fluid flush at all four wheels. It seems that the previous owner hasn't changed brake fluid for years.

My question is, judging from the video, do I have a sticky caliper? I would expect there might be some tolerance for pads coming into contact with the rotor, just not sure whether my case is in the normal range. Could this be the culprit for my steering wheel jerk at light braking?

Thanks very much!

I would agree that it appears you have a sticky caliber or more likely a high spot in the rotor. Are the rotors new? Age if not new? Have they ever been turned on a lathe?
To test if you have a high spot, you would need to measure to rotor thickness all the way around. A visual inspection might show something first.


I have an ever so slight back and forth shimmy in the steering wheel under the same conditions (car still tracks straight under braking), but haven't tried spinning the wheels to see if one has more resistance than the other. It started after I did the brake fluid flush as well. I'd be interested in hearing if other people's suggestions beyond warped rotors.

I believe your shudder is a bit different from GreatFrog's original post. You seem to be experience front control arm bushing failure. To test this, jack the front end up, and try to wiggle the front wheel back and forth. If it wiggles, and shows very little resistance, then your FCAB's might have failed.

[NoVAphotog]

Hi guys, just bought a 2003 ZHP with only 34k miles on it. Everything is working beautifully except that the steering wheel jerks slightly when tapping the brake (light braking only, heavy braking does not produce the jerk). The mechanic inspection showed front control arm ball joints are in great shape. I just replaced front control arm bushings myself and it didn't cure the problem.

I jacked up the car at front and spun both the front wheels. The right front wheel spun completely freely. While I could feel some resistance rotating the left front wheel. I could hear periodic grinding noise from brake pad coming into contact with the rotor while the wheel spun, and it came to a completely stop after 2~3 revolutions. I took videos of both wheel spinning:

Front right wheel spinning freely

https://www.youtube.com/watch?v=CZMXN_XNpsg

Front left wheel got some resistance

https://www.youtube.com/watch?v=hOy5gkpEGbk

The video was taken after doing a brake fluid flush at all four wheels. It seems that the previous owner hasn't changed brake fluid for years.

My question is, judging from the video, do I have a sticky caliper? I would expect there might be some tolerance for pads coming into contact with the rotor, just not sure whether my case is in the normal range. Could this be the culprit for my steering wheel jerk at light braking?

Thanks very much!

Thanks for these videos. I have this exact same thing except on the front right. Do not have the steering wheel jerk at light braking though and I just replaced the FCABs with the Z4M ones in August. Had a shimmy on braking at higher speeds which went away after removing the spacers and new FCABs. As for the braking situation, do you notice when driving at low speeds in the morning or soon after startup you hear that same sound it makes when you spun it while driving, obviously softer, but still like a slight rubbing?

[GreatFrog]

hmmm. i had that issue when i first bought my ZHP and it was the FCABs.

what FCABs did you install?

peter

Hi Peter,

Thanks for your input. I replaced them with Lemforder's. I think they are OEM supplier for FCABs. I doubt if it is the FCAB to blame though. Because if it is the FCAB, shouldn't I also get shimmy steering wheel at heavy brakings? Because the heavy brakings put more stress on them and should amplify the problem, right?


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[GreatFrog]

I would agree that it appears you have a sticky caliber or more likely a high spot in the rotor. Are the rotors new? Age if not new? Have they ever been turned on a lathe?
To test if you have a high spot, you would need to measure to rotor thickness all the way around. A visual inspection might show something first.



I believe your shudder is a bit different from GreatFrog's original post. You seem to be experience front control arm bushing failure. To test this, jack the front end up, and try to wiggle the front wheel back and forth. If it wiggles, and shows very little resistance, then your FCAB's might have failed.

Hello TheFinanceGuy,

I think you are pointing me to the right direction. Yes, the rotor is OOOOLD. They were not changed during the last brake service and I believe they have been sitting on the car since 2003 when the car rolled out of the factory. They are worn down to or even below min thickness. I just didn't realize that there could be a high spot issue with aged rotors, cause I never heard of it. Now it makes sense to me. I will change the rotors and report back if cures the problem. Thanks very much!


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[GreatFrog]

Thanks for these videos. I have this exact same thing except on the front right. Do not have the steering wheel jerk at light braking though and I just replaced the FCABs with the Z4M ones in August. Had a shimmy on braking at higher speeds which went away after removing the spacers and new FCABs. As for the braking situation, do you notice when driving at low speeds in the morning or soon after startup you hear that same sound it makes when you spun it while driving, obviously softer, but still like a slight rubbing?

Hi NoVAphotog,

Thanks for your reply. I never heard that noise when I was in the cabin. I will pay attention to it next time when I drive the car and will report back. Thanks!


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[BMWCurves]

I believe your shudder is a bit different from GreatFrog's original post. You seem to be experience front control arm bushing failure. To test this, jack the front end up, and try to wiggle the front wheel back and forth. If it wiggles, and shows very little resistance, then your FCAB's might have failed.

Now that I think about it, I can't remember if I still have this issue since I replaced the FCABs with Genuine BMW Z4M FCABs recently (I've barely had the car). I'll check again when I finally get it back from the mechanic today. Appreciate the suggestions.

EDIT: Got the car back from the mechanic this morning, definitely doesn't do the shimmy like it did before the FCABs were replaced. Seems that has indeed solved my problem.

[GreatFrog]

I would agree that it appears you have a sticky caliber or more likely a high spot in the rotor. Are the rotors new? Age if not new? Have they ever been turned on a lathe?
To test if you have a high spot, you would need to measure to rotor thickness all the way around. A visual inspection might show something first.



I believe your shudder is a bit different from GreatFrog's original post. You seem to be experience front control arm bushing failure. To test this, jack the front end up, and try to wiggle the front wheel back and forth. If it wiggles, and shows very little resistance, then your FCAB's might have failed.

At a second thought, wouldn't high spot in rotor produce periodic shake in the steering wheel? i.e. every time the high spot meets the pad? I can only feel one back and forth movement at the steering wheel when initially applying the brake.


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