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Suspension & Braking
Have some questions about suspension or brake setups for your E46 BMW? Get all your answers here!

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Old 01-03-2013, 10:32 AM   #1
JokerElite
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Steering Wheel Twitch when Braking

I've been having this problem since a few days after rebuilding the front passenger side brake caliper because I had a "sticky caliper".

Basically, what happens is when braking, when the brake pedal is down about 50% the steering wheel twitches once and there's a kind of thump noise that sounds like it's coming from the front passenger side caliper. It doesn't do that when the pedal is less than 49% down or after 51% down. But when releasing it and passing the 50% mark, it'll twitch again.

Also after the steering wheel twitch and the noise (or when the brake pedal is pressed down more than 50%) the car will slightly pull to the right.

Not sure what could be causing this. I followed caliper rebuild DIYs thoroughly and the process went smoothly. I bled the brakes but could there be more air in the system? Any help would be appreciated.

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Old 01-03-2013, 11:01 AM   #2
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Most likely front control arm bushings. How many miles are on the car?
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Old 01-03-2013, 11:32 AM   #3
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I've been having this problem since a few days after rebuilding the front passenger side brake caliper because I had a "sticky caliper".

Basically, what happens is when braking, when the brake pedal is down about 50% the steering wheel twitches once and there's a kind of thump noise that sounds like it's coming from the front passenger side caliper. It doesn't do that when the pedal is less than 49% down or after 51% down. But when releasing it and passing the 50% mark, it'll twitch again.

Also after the steering wheel twitch and the noise (or when the brake pedal is pressed down more than 50%) the car will slightly pull to the right.

Not sure what could be causing this. I followed caliper rebuild DIYs thoroughly and the process went smoothly. I bled the brakes but could there be more air in the system? Any help would be appreciated.
Agree with jesse. Check this out.


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Old 01-03-2013, 11:36 AM   #4
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FCABs can cause that. How is it when you go over uneven road surfaces. Does the steering wheel pull then?
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Old 01-03-2013, 01:05 PM   #5
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Most likely front control arm bushings. How many miles are on the car?
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Old 01-03-2013, 04:23 PM   #6
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Ck your brake rotors.

Ck lcab.

Then replace steering guibo.
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Old 01-03-2013, 05:24 PM   #7
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Someone on another forum suggested it's not the FCABS and explained why. The car drives straight over uneven roads. The only time it pulls is when I'm braking, and when the pedal is past 50% down. I highly doubt it's the FCABS.

Since I just rebuilt the caliper it's probably something with that brake. But I don't know what exactly.
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Old 01-03-2013, 05:41 PM   #8
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Someone on another forum suggested it's not the FCABS and explained why. The car drives straight over uneven roads. The only time it pulls is when I'm braking, and when the pedal is past 50% down. I highly doubt it's the FCABS.

Since I just rebuilt the caliper it's probably something with that brake. But I don't know what exactly.
No. it's the FCABs. that's textbook FCABs. raise the car and turn the wheel all the way to one side (either side is fine) then shake the wheel with your hand. Can you see the control arm move within its control arm bushing bracket?
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Old 01-04-2013, 03:36 AM   #9
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Someone on another forum suggested it's not the FCABS and explained why. The car drives straight over uneven roads. The only time it pulls is when I'm braking, and when the pedal is past 50% down. I highly doubt it's the FCABS.

Since I just rebuilt the caliper it's probably something with that brake. But I don't know what exactly.
If you ignore FCABs and other steering alignment issues then you are looking at unequal traction between pads and disc on both each side ie: the right caliper is gripping or engaging before the left one. Since that is the caliper you have replaced it is likely that the new caliper is acting more efficiently than the old one on the opposite side. This is why you should really replace both sides when you replace either pads, discs or calipers. Other possibilities? Air in left caliper pipe? Contaminated pads on left affecting traction? Uneven pad thickness on either side? You should bleed the system again for sure. Both sides not just the passenger side. Open both bleed screws at the same time. But sounds to me like you need to take a look at the efficiency of the remaining caliper with view to replacing that one as well.

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Old 01-05-2013, 11:49 AM   #10
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No. it's the FCABs. that's textbook FCABs. raise the car and turn the wheel all the way to one side (either side is fine) then shake the wheel with your hand. Can you see the control arm move within its control arm bushing bracket?
Will try this. Any other ways of telling it's the FCABs?

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If you ignore FCABs and other steering alignment issues then you are looking at unequal traction between pads and disc on both each side ie: the right caliper is gripping or engaging before the left one. Since that is the caliper you have replaced it is likely that the new caliper is acting more efficiently than the old one on the opposite side. This is why you should really replace both sides when you replace either pads, discs or calipers. Other possibilities? Air in left caliper pipe? Contaminated pads on left affecting traction? Uneven pad thickness on either side? You should bleed the system again for sure. Both sides not just the passenger side. Open both bleed screws at the same time. But sounds to me like you need to take a look at the efficiency of the remaining caliper with view to replacing that one as well.
Do calipers/brakes normally become less efficient/effective over time? I guess a rebuilt one is different than one that doesn't show any problems?
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Old 01-05-2013, 02:05 PM   #11
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Do calipers/brakes normally become less efficient/effective over time? I guess a rebuilt one is different than one that doesn't show any problems?
For the record. Yes. Most things with seals do. When caliper seals leak it may not be noticeable. Minute leaks might accumulate behind the boot and dry up. Calipers get jolly hot. Nevertheless, air gets into the system past the seals and instead of the hydraulic force from the pedal acting on the piston it squashes the air instead leading to a reduction in the force available for braking. So it depends on the condition of the caliper left behind. It generallly works on this premise. You find it necessary, for some reason, to replace one caliper. Assuming both calipers are of the same vintage, it is only reasonable to propose that internal seals wear at the same rate in both calipers over time. There are other factors, of course, that might accelerate the deterioration of one with respect to the other : split rubber boot for example and corrosion preventing the piston from fully retracting. But in an ideal world both calipers should apply the same force to their piston and thereby to the pads at the same time resulting in the same traction between pads and disc. The whole point of changing both discs, both sets of pads and both calipers when they need replacing is so that they are the same vintage at the outset and so that they act and deteriorate uniformally. Like I said, you need to ensure that both are properly bled and, if the problem persists, you need to check the remaining caliper, pads (for contamination) and disc. Its all about ensuring uniformity of applied braking. Although, as most have already pointed out (myself included), it is most likely you FCABS.

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Old 01-05-2013, 02:11 PM   #12
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For the record. Yes. Most do things with seals do. When caliper seals leak it may not be noticeable. Minute leaks might accumulate behind the boot and dry up. Calipers get jolly hot. Nevertheless, air gets into the system past the seals and instead of the hydraulic force from the pedal acting on the piston it squashes the air instead leading to a reduction in the force available for braking. So it depends on the condition of the caliper left behind. It generallly works on this premise. You find it necessary, for some reason, to replace one caliper. Assuming both calipers are of the same vintage, it is only reasonable to propose that internal seals wear at the same rate in both calipers over time. There are other factors, of course, that might accelerate the deterioration of one with respect to the other : split rubber boot for example and corrosion preventing the piston from fully retracting. But in an ideal world both calipers should apply the same force to their piston and thereby to the pads at the same time resulting in the same traction between pads and disc. The whole point of changing both discs, both sets of pads and both calipers when they need replacing is so that they are the same vintage at the outset and so that they act and deteriorate uniformally. Like I said, you need to ensure that both are properly bled and, if the problem persists, you need to check the remaining caliper, pads (for contamination) and disc. Its all about ensuring uniformity of applied braking. Although, as most have already pointed out (myself included), it is most likely you FCABS.
Indeed some of the problem seems to be the FCABs. Just checked them and the front passenger one looks bad. Will be replacing both FCABs as well as rebuilding the other caliper. Thanks for all the help throughout my troubles RayPooley, it really means a lot and makes it easier for me!

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Old 01-05-2013, 02:31 PM   #13
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Indeed some of the problem seems to be the FCABs. Just checked them and the front passenger one looks bad. Will be replacing both FCABs as well as rebuilding the other caliper. Thanks for all the help throughout my troubles RayPooley, it really means a lot and makes it easier for me!

Wow dude. That one might as well not exist. Don't replace just that one. Replace them BOTH. Same reason as explained for brake components. The policy also applies to suspension components, struts, shocks, springs, anything to do with the stability of the vehicle. But that's the one on the right (passenger side in the US). So you can undestand what's happening when you apply the brake. The weight of the car pushes forward against the steering components when you brake. That FCAB is supposed to prevent the steering assembly from moving backwards. Its easy to see why it isn't doing its job. This distortion manifests itself in tha car as the steering wheel turning to the right because the whole steering assembly on the right hand side is moving backwards. You need to get this done as a matter of urgency and hope it hasn't damaged any of the other ball joints in the steering gear/suspension assembly. BTW, you DO NOT necessarilly need an alignment after this job is done. Take it for a run after the job. If it is tramlining then you would need to check other ball joints for excessive wear and fix them before an alignment would be expected to truly align the steering. But get these replaced first of all before you go anywhere in that vehicle. It is dangerous in it present condition. See the vid I posted earlier. Not a big job.

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Old 01-05-2013, 02:55 PM   #14
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it is going to be your other caliper . A new rebuilt caliper will react quicker because the seal is firm. All it is is a new oring, but it seals the caliper more precisely.

Just buy a rebuild kit (oring) and just rebuild it.

You can buy it at autohausaz.com

Last edited by BMWCaptain; 01-13-2013 at 10:58 PM.
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Old 01-05-2013, 02:57 PM   #15
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it is going to be your other caliper . A new rebuilt caliper will react quicker because the seal is firm. All it is is a new oring, but it seals the caliper more precisely.

Just buy a rebuild kit (oring) and just rebuild it.

You can buy it at Azautohaus.com
No its not. Check out his passenger side FCAB in the vid above.
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Old 01-05-2013, 03:38 PM   #16
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Yeah, both are going to be replaced. I just went for a short drive somewhere and noticed something. Replacing the FCABs will fix the pulling possibly. But there's still that steering wheel twitch when the brake pedal is at 50%. When braking usually it happens twice, because you press the pedal past that amount and then release it past that amount. When I was driving and braked to stop, it twitched once at the 50% mark. Then when I was at a complete stop I released the pedal and it twitched again, this can't be the FCABs right? Because the car isn't moving? And it can't be the other caliper being a little more worn either for the same reason.

I'm not sure what's causing this thump. It feels like it's the piston some how on the side I rebuilt. It seems like it when you press the brake it can go smoothly from 1%-50%. But after you press it 50% down, maybe the piston just comes out to 100%.

By the way, the pulling doesn't happen until the thump does. I could be driving at a faster speed and brake before the pedal is 50% down and come to a stop with no pulling at all or thumping. It's kind of difficult to explain.
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Old 01-05-2013, 03:48 PM   #17
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Yeah, both are going to be replaced. I just went for a short drive somewhere and noticed something. Replacing the FCABs will fix the pulling possibly. But there's still that steering wheel twitch when the brake pedal is at 50%. When braking usually it happens twice, because you press the pedal past that amount and then release it past that amount. When I was driving and braked to stop, it twitched once at the 50% mark. Then when I was at a complete stop I released the pedal and it twitched again, this can't be the FCABs right? Because the car isn't moving? And it can't be the other caliper being a little more worn either for the same reason.

I'm not sure what's causing this thump. It feels like it's the piston some how on the side I rebuilt. It seems like it when you press the brake it can go smoothly from 1%-50%. But after you press it 50% down, maybe the piston just comes out to 100%.

By the way, the pulling doesn't happen until the thump does. I could be driving at a faster speed and brake before the pedal is 50% down and come to a stop with no pulling at all or thumping. It's kind of difficult to explain.
Its a process man. Fix the FCABS first and then see what happens after that. But one thing is for sure. While your steering is flopping around like that you can't really diagnose whether your braking is uniform or not. One step at a time. Try to understand that at this point in time you do not have any FCABS. They have gone. So ANYTHING that the sterring does is largely unpredicatable because its structure is incomplete. At the moment you are puttting loads and strain on all components that they were not designed to take. Even the the three bolts that are holding your struts in place against teh body and the metal surrounding them at the top of the strut towers which can fatique and fracture. That would write off teh car.

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Old 01-05-2013, 04:40 PM   #18
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Its a process man. Fix the FCABS first and then see what happens after that. But one thing is for sure. While your steering is flopping around like that you can't really diagnose whether your braking is uniform or not. One step at a time. Try to understand that at this point in time you do not have any FCABS. They have gone. So ANYTHING that the sterring does is largely unpredicatable because its structure is incomplete. At the moment you are puttting loads and strain on all components that they were not designed to take. Even the the three bolts that are holding your struts in place against teh body and the metal surrounding them at the top of the strut towers which can fatique and fracture. That would write off teh car.
That's true. I planned on replacing both FCABs anyway. I was just wondering what could be the sole cause of the thumping. Will be ordering these parts soon.
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Old 01-05-2013, 06:24 PM   #19
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Worn FCABs can do crazy things. The improvement you'll feel afterwards will be pretty awesome. If your FCABs are worn and you haven't done your RTABs either, it might be time to start thinking about doing those as well.
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Old 01-07-2013, 09:48 AM   #20
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I plan on doing the RTABs in the spring or summer. For now I ordered both FCABs and another brake caliper rebuild kit for the other front caliper. Just waiting for these to come in so I can start doing some work.
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