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Old 06-19-2018, 12:57 PM   #1
rumatt
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Pulsing f*cking brake rotors

The E46 has been fantastic since getting it back from JV, except one thing. I'm still struggling with pulsing brake rotors. I put on new rotors and pads a while back and it was perfect - for about 2 weeks. Then it slowly came back.

How to fix it

I have bed them multiple times. It makes it better, but doesn't fix it entirely. I can still feel the pulsing ever so slightly (I have PTSD over this so I can feel it coming on well before most people ) and sure enough it gets worse and worse over time.

Am I not bedding them enough? I usually stop when I feel the brake pedal getting soft because I'm worried I'm going to boil the brake fluid. Am I supposed to keep going?

Zeckhausen recommends using race pads to remove a layer from your pads to start fresh. I might try this and then re-bed them with the stock pads... (or bed with the race ones?). I need to try something different this time so it's not more of the same.


How to prevent it

I do my best to avoid stopping with my foot on the brake, to the point of being obsessive. Maybe I'm doing it without realizing it? But I mean, how fragile should these things be? I have to be able to stop on a hill once in a while without needing to re-bed my brakes, right?

I also don't drive very aggressively any more or get them particularly hot. Maybe that's part of the problem? Maybe if I get them bed in properly once the problem will go away?

And this hasn't happened on the Cayman or the Colorado so I'm having a hard time blaming my driving. And with the auto in the truck I'm on the brake every time I stop to prevent the truck from pulling me forward. And at 3K miles the rotors are smooth as could be.

Last edited by rumatt; 06-19-2018 at 01:13 PM.
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Old 06-19-2018, 01:27 PM   #2
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Hmmm...

I'm more inclined to think of something more subtle. Are your calipers sliding smoothly and evenly? Perhaps it's binding more on one side than the other causing uneven pressure. I suspect it's far too recent to be able to see physical signs of said wear on the pads or rotors, right?

It's just a theory.

Can you narrow it down to a particular axle or wheel?
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Old 06-19-2018, 01:46 PM   #3
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It's definitely the front rotors. Changing them makes the problem go away entirely. Until it comes back.

I can't really tell if it's just one side or both. Part of me wants to say it feels like it's coming from the driver side, but I'm not sure what it is that makes me think that.
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Old 06-19-2018, 01:59 PM   #4
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If the caliper(s) is hanging up a little would it cause the rotor to heat unevenly and warp? Basically what FC said, maybe a pad is dragging a bit and heating a portion of the rotor
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Old 06-19-2018, 02:14 PM   #5
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Bedding does make it better though. Would it do that if they were actually warped?
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Old 06-19-2018, 02:21 PM   #6
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I'm a certified brake mechanic and my first guess was that you have at least one fucked up caliper that's causing uneven wear.
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Old 06-19-2018, 02:32 PM   #7
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Does your certification allow you to drive to my house and fix my car?
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Old 06-19-2018, 02:33 PM   #8
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If I put race pads on the car, drive around for a while, and the vibration is gone then it blows a hole in the damaged caliper theory, right?
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Old 06-19-2018, 02:55 PM   #9
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Quote:
Originally Posted by rumatt View Post
If I put race pads on the car, drive around for a while, and the vibration is gone then it blows a hole in the damaged caliper theory, right?
EDIT: Yes, likely. But at that point I'd be out of ideas as to what is causing the issue. I am not an expert in braking systems at all. But here is my analysis nevertheless from what little I know.

The pulsating thing can only be caused by one of two things (as far as I can think of right now):

1. Something is causing you brakes to wear unevenly and and you are feeling the uneven surface as it comes around every revolution.

2. The hydraulic pressure itself is going up and down. I don't know enough to postulate a reasonable theory for this could happen, so I am gonna conveniently ignore this possibility.

So on to things that can warp your rotor:

A. Uneven wear due to uneven pressure as I explained on the post above.
B. Thermal shock if you splash your (VERY hot) rotors on a deep puddle.
C. Intermittently sticking capilers. Weird, and unlikely without you noticing something is really wrong.

Last edited by FC; 06-19-2018 at 03:13 PM.
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Old 06-19-2018, 02:59 PM   #10
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Quote:
Originally Posted by rumatt View Post
If I put race pads on the car, drive around for a while, and the vibration is gone then it blows a hole in the damaged caliper theory, right?
Hmm, I'm stumped.
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