Braking Vibration - Confirm my diagnosis

[kring]

Hi all,

I've been struggling with a fairly violent brake vibration on my 92 525i for awhile now. The vibration happens under light-to-medium braking starting at about 50 MPH and getting worse until about 40 MPH, where it promptly stops. It started about the same time I changed my rear pads and rotors, so of course my first thought was to blame the rotors. I have since replaced all 4 rotors (including significant time spent with WD40 and a wire brush thoroughly cleaning the rotor mounting surface) and still the vibration persists.

I've also had 4 new tires installed since the vibration started, with no difference there, either.

My next thought is that this is a control/thrust arm problem. I do have the characteristic 55 MPH-ish non-breaking vibration, but it is nowhere near as severe as the braking vibration. Also, I've inspected the bushings visually, and to my untrained eye they don't look "that bad".

The caliper on my front drivers side does look a little sketchy, though. Could it be related? I've included a picture below:

http://www.kotachrome.com/P1020270.JPG

Thanks for your thoughts!

Kevin

[Alexlind123]

Im afraid i cant help you with your braking problem, but since you have the 55 shimmy, it might be a good idea to fix that first and then if the braking problem sitll exists try to fix it then.

[Traian]

That sounds like the thrust arm bushings. I had a very similar problem, very violent vibration only under light braking from about 55 mph (so a tad faster). New arms and bushings solved it. It will probably cure your other shimmy as well.

[632 Regal]

kevin, that seal on the caliper piston isnt a good thing, they make kits to rebuild them. Yours maybe rusty from that bad seal and could be binding a bit causing the rotor to overheat and cause the shimmy. I agree that the thrust arm bushings are most likely shot, if you can see micro cracks in the rubber part its time for new ones. Get Lemforder arms with the 750 bushing pressed at bmaparts.com, call them and you wont have to deal with their online site. They also have the caliper rebuild kits.

[Kalevera]

Were the front or rear rotors cut or turned, versus being replaced with new parts?

[632 Regal]

also do you have factory stock wheels? If not you probably need hubcentric rings.

[uscharalph]

Hi all,

I've been struggling with a fairly violent brake vibration on my 92 525i for awhile now. The vibration happens under light-to-medium braking starting at about 50 MPH and getting worse until about 40 MPH, where it promptly stops. It started about the same time I changed my rear pads and rotors, so of course my first thought was to blame the rotors. I have since replaced all 4 rotors (including significant time spent with WD40 and a wire brush thoroughly cleaning the rotor mounting surface) and still the vibration persists.

I've also had 4 new tires installed since the vibration started, with no difference there, either.

My next thought is that this is a control/thrust arm problem. I do have the characteristic 55 MPH-ish non-breaking vibration, but it is nowhere near as severe as the braking vibration. Also, I've inspected the bushings visually, and to my untrained eye they don't look "that bad".

The caliper on my front drivers side does look a little sketchy, though. Could it be related? I've included a picture below:

http://www.kotachrome.com/P1020270.JPG

Thanks for your thoughts!

Kevin
My BMW just started the same violent shimmy around 55 mph. Hopefully it's the rotors which I plan on replacing in March.

I know the shiimy isn't due to any of the suspension parts. I've recently replaced the upper and lower arms, the idler arm, the left right and center tie rods and the sway bushings alon with the lft and right sway ties. The car handles extremely well. So like I said hopefully it's the rotors.

[gale]

My BMW just started the same violent shimmy around 55 mph. Hopefully it's the rotors which I plan on replacing in March.

I know the shiimy isn't due to any of the suspension parts. I've recently replaced the upper and lower arms, the idler arm, the left right and center tie rods and the sway bushings alon with the lft and right sway ties. The car handles extremely well. So like I said hopefully it's the rotors.

I can say with a high degree of certainty that it's your rotors. I just went thru that ordeal with mine and put new rotors & pads on it today and just got back from bedding them in:

http://www.zeckhausen.com/bedding_in_brakes.htm

The rubber boot on your caliper piston looks like it is either torn or has merely pulled off of the lip of the caliper and needs to be pulled back into the groove. New boots are cheap if it's torn. I doubt the caliper is making it shimmy but it could have contributed to a warped rotor if the caliper were sticking and let the pads drag on the rotor for a long time and caused the rotor(s) to overheat.

I put new Balo blanchard ground rotors & Raybestos QS ceramic pads and so far I like them very much, firm even controlled braking performance right from the beginning. It's only been 20 miles or so and will have to give them more time to come to a conclusion, but as for the shimmy, it's gone completely. I just did new tires & a Hunter 9700 S roadforce balance on it, the wheels are like new, the shop said the roadforce numbers were great, and it drove smooth until applying the brakes with the old rotors and the shop said it was definitely rotors (as opposed to control arms), so took them at their word, bought new rotors -- problem solved!

[Alexlind123]

Avoid having the tire shop install new tires or wheels. I know that many times this is hard to do, but they will almost without fail torque your lug bolts way to high or with uneven torques. The most common cause of warped rotors is uneven or incorrect lug bolt torque.

[uscharalph]

Avoid having the tire shop install new tires or wheels. I know that many times this is hard to do, but they will almost without fail torque your lug bolts way to high or with uneven torques. The most common cause of warped rotors is uneven or incorrect lug bolt torque.
Is that really true???

[kring]

Thanks for the input, everyone. To answer some questions:
lowell, all 4 replacement rotors were new parts.
632 Regal, my wheels are the stock 15 in bottlecaps.

gale, when you say it is almost certainly a rotor problem, are you talking specifically to uscharalph, or would you apply that to my situation as well? I'm hesitant to replace the rotors again, as you might imagine, since it really didn't make any difference at all the first time. If it really does sound like a rotor problem, I would be inclined to believe that the rotor mounting surface itself is bent (though it doesn't look it...)

In any case, I think my next step will be to replace the thrust arms. As Alexlind123 said, since they probably need replacing anyway I might as well do that first and see if it fixes the brake vibration.

Thanks again to everyone for the advice.

Kevin

[uscharalph]

Thanks for the input, everyone. To answer some questions:
lowell, all 4 replacement rotors were new parts.
632 Regal, my wheels are the stock 15 in bottlecaps.

gale, when you say it is almost certainly a rotor problem, are you talking specifically to uscharalph, or would you apply that to my situation as well? I'm hesitant to replace the rotors again, as you might imagine, since it really didn't make any difference at all the first time. If it really does sound like a rotor problem, I would be inclined to believe that the rotor mounting surface itself is bent (though it doesn't look it...)

In any case, I think my next step will be to replace the thrust arms. As Alexlind123 said, since they probably need replacing anyway I might as well do that first and see if it fixes the brake vibration.

Thanks again to everyone for the advice.

Kevin
Probably the way to go.

[uscharalph]

I can say with a high degree of certainty that it's your rotors. I just went thru that ordeal with mine and put new rotors & pads on it today and just got back from bedding them in:

http://www.zeckhausen.com/bedding_in_brakes.htm

The rubber boot on your caliper piston looks like it is either torn or has merely pulled off of the lip of the caliper and needs to be pulled back into the groove. New boots are cheap if it's torn. I doubt the caliper is making it shimmy but it could have contributed to a warped rotor if the caliper were sticking and let the pads drag on the rotor for a long time and caused the rotor(s) to overheat.

I put new Balo blanchard ground rotors & Raybestos QS ceramic pads and so far I like them very much, firm even controlled braking performance right from the beginning. It's only been 20 miles or so and will have to give them more time to come to a conclusion, but as for the shimmy, it's gone completely. I just did new tires & a Hunter 9700 S roadforce balance on it, the wheels are like new, the shop said the roadforce numbers were great, and it drove smooth until applying the brakes with the old rotors and the shop said it was definitely rotors (as opposed to control arms), so took them at their word, bought new rotors -- problem solved!
New Rotors and Pads fixed the shimmy 100% in my case.

[joshua43214]

Is that really true???

Yes