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 :lol:) 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. :dunno:

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?

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.

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

Bedding does make it better though. Would it do that if they were actually warped?

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.

Does your certification allow you to drive to my house and fix my car? :D

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.

Hmm, I'm stumped.

I think it requires him to. :D

Well, I didn't do it yet, so....

depends how they heat up and how they are worn... ie: if they are significantly thinner than your current pads, they may not drag (or drag as much) and not cause the rotors to heat.

Does it do it all the time / everytime, or only after they warm up? Does it matter how hard you press the brakes (does it get worse if you press harder or does it only start after a certain amount of pressure)? Any residual vibration not under braking?

It's there all the time. Any speed, any pressure. But as you would expect, the vibrations are faster at higher speeds, and stronger under firm braking.

Braking hard at high speed sucks, and makes me curse at my rotors.

What brake pads are you using?

Textar.
https://www.ecstuning.com/b-textar-p...116779652~tex/

I've had this forever. Dealer replaced rotors (and eventually calipers / mounting hardware) multiple times under new car warranty. Out of warranty, I tried various combinations of OEM / aftermarket rotors / calipers, and nothing fixes it 100%. I get the best results with Bavarian Autosport slotted + drilled rotors and OEM pads (had tried various aftermarket pads).

A good re-bedding clears the problem up for a while, then it comes back. So definitely not warpage - just some sort of build-up on the rotors.

Installed four new rotors and pads on the f10 535i at 49k miles. It was pulsing badly and the rotors were visibly rusty. I used Zimmermann rotors and I think Textar (OEM-equivalent) pads. After a few thousand miles, the pulsing is coming back.... To top it off, I'm feeling very slight pulsing on the Boxster (at 17k miles). :ack:

Could bad roads (braking on bumps e.g.) cause issues over time? I see a commonality among Rumatt, Terry and I and that's where we live and drive. :eeps:

I'm paranoid about holding down the brake pedal at a stop, will occasionally use hand brake or move car a bit to avoid hot spots.

I also have Zimmerman rotors.

My theory on the commonality is that we don't drive our cars every day. My theory is that the rotors get slightly rusty from rain / humidity, but not in the spot where the pads are resting on the rotors. Driving scrapes the rust off off the rest, but the rotor is never the same from that point forward.

Should I do an experiment where I remove my brake pads every time I park the car? :ack:

Double blind . . .you'll have to remove the rotors too :mad2:

Removing the rotors and store them in a humidity controlled environment.

Double blind means someone else does it and I don't know whether they did or not. Can you be that person? :D

I think it would be easy to tell that I didn't :D

The 535i pads were worn and the rotors needed replacing due to heavy rust; the OEM rotors were the most rusty brakes I've ever seen on any car at 50k miles. I'm not sure if it was Baltimore (where the car lived up to 42k miles) or the material that BMW has switched to. The Zimm's on the 528i never rusted or pulsated. They were installed at 50 or 60k and going strong at 130k. The 17-year old OEM rotors on the M3 never pulsated and that car wasn't driven frequently.

I don't see how - in my case, it is definitely pad material build-up on the rotors, since I can get rid of it with aggressive re-bedding-in. Now, I do have to get my rims straightened at Wheel Collision every 2 years, but that's a different issue. :irate:

May have more to do with driving style - I'm probably the only person that ever reviewed soft-compound A048's on Tire Rack and listed my driving style as "relaxed". :D

Is it just that we drive like old men? Never get them hot enough?

I may not be perfect at stop signs but I'm so obsessive about it that I refuse to believe that's the problem. If it is then no non-enthusiast would ever be able to drive a BMW without the brakes shaking the car to pieces.

Matt, there's nothing wrong with your calipers. At least, when I had the car there was nothing wrong with them. I've seen the stock BMW calipers go wrong, but usually it's when someone tries to grease the slide pins. And then the symptom is the brakes get hot because they aren't releasing fully.

When I had my ZHP I had the same problem with the brakes (occasional pulsation). I believe what causes it is not enough hard braking events. I never found a better cure than an occasional full-panic-braking stop from freeway speeds.

The Mazdaspeed suffers from this occasionally as well. It is what it is. :dunno:

I swapped my old Hawk Performance pads on today and made a trip to Home Depot. I did a few hard stops but didn't bed them - theory being the goal is to scrap the hell out of the rotors, not create an optimal braking surface.

In gentle stops they seem fine but in hard stops they still pulse like a bitch. I'm going to leave them on for a few days while commuting to work and see what happens.

I'm still failing here. :mad:

Short version: Bedding with race pads took the rotors from awful (shaking the front end to pieces while braking) to very good. But it's not right, it's getting worse again, and I'm cranky. I'm now avoiding driving the car because the brakes are annoying.

Long version

Here's exactly what has taken place:

1. I put on Hawk race pads on for a week (no bedding), screeching everywhere I went, with Dave Z's theory that it scrapes a layer off your rotors.
2. Bed rotors with the Hawk pads, making sure to literally never touch the brakes afterward - even coming to a full stop in my driveway.
3. Next day, swapped on Textar pads and bed again. Same procedure. The brakes were f*cking hot.
4. Next day I evaluated them and I'd say it was 95% better. Braking under 60 MPH felt pulse free. Hard braking from 80 you could still feel a pulse. From 100 it was very noticible - a subtle, high speed pulse.
5. I repeated the bedding with the Textar pads. I saw no real improvement.
6. It's now been a couple weeks since the above, and as expected the pulsing is slowly getting worse. I can now hear and feel it at braking under 60MPH.

Unless someone has a better idea, I'm going to try the following things in this order

1. Try a series of 3 bedding sessions with the Textar pads, and see if that helps.
2. I guess I'll try another set of new rotors, maybe a different brand? Slotted like Terry Recommended?
3. Give up, push the car into the lake and buy something new.

start over with new rotors and new pads

Right. But I started from new pads and rotors once already. Doing it again only makes sense if I think I did something wrong, and plan to do it differently this time.. Right?

What am I doing differently?

Maybe I didn't bed them aggressively enough when they were new? I did bed them though. :(

Too much friction?

Revert to new OEM of everything?

Cheap rotors and aggressive pads are my suggestion.

I still think something is probably hanging up and heating the rotor(s) non uniformly. Can you see a lot of pad deposits on the rotor? I'd see if a cylinder is bent or stuck or slow to retract.

Huh?

These were new OEM-ish parts. :dunno:

Do you have specific suggestions for each? I've got 2 brand new sets of textar pads. Would prefer not to toss them, but oh well.

I will take a look at them at some point. It probably won't be for a week or two though.

Did I use too many words? ;) Meant friction between the pads and rotors. Are the pads grabbing too aggressively, or could they be grabbing inconsistently and causing a pulsing?

Could it be a failing ABS sensor, falsely reporting lockup? How about wheel bearings?

No that's not it.
Yes is the problem.
I don't think it's any of those things. Everything is consistent with inconsistent friction surface on the rotors.

I wonder if you have a bad hub. Check for wheel bearing play.

How could it be the hub if it mostly goes away with bedding and then comes back with a vengeance?

Honestly, I think I'm suffering from the same. My new Zimm rotors and textar pads on the 535i pulse like crazy. I haven't had the time (and space) to go out and bed them, but in my heart of hearts, I don't think it's going to cure it.