Is my brake disk warped? - Mercedes-Benz Forum

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post #1 of 22 (permalink) Old 12-29-2014, 09:15 PM Thread Starter
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Is my brake disk warped?

I've been hearing an annoying rubbing noise from front right wheel since replacing the front brake pads. I drive my car only occasionally, maybe 1000 km in 2+ months, so I can't say I've driven enough for the new pads to get bedded. To make sure that the noise was indeed coming from the pad contacting the disk I jacked up the car and rotated the wheel and verified that the pads were really contacting the disk surface. The noise was the same. Now I have 2 questions:


1. Is it normal that brake pads are in contact with the brake disk even when the brake pedal is not pressed? I thought the rotor should be able to rotate freely when no braking is applied.

2. And the main concern: When I rotate the wheel I can see that it rotates easily for the 90% of the circle, but it gets hard at the rest 10%. So this makes me think that the disk is warped and that's what makes the noise? Am I correct in my suspicion?
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post #2 of 22 (permalink) Old 12-29-2014, 09:28 PM
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When I have replaced pads, they have not usually rubbed against the disk.

When they did rub against the disk, I treated it as a brake caliper problem. I removed the caliper and took it to my local brake shop. They removed the piston (compressed air) and polished it, cleaned out the fluid area of the caliper of gunk, and re-installed the piston. That restored the full travel of the piston and stopped the rubbing.

Have you been flushing your brake fluid every 24 months?

If not, your brake calipers may be mucked up.

Warped rotors can often be identified by a "pulsing" in brake pedal feel when braking.
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post #3 of 22 (permalink) Old 12-29-2014, 09:41 PM
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It does sound like a caliper issue to me also.

It may just be the sliding pins needing to be cleaned up and greased well.
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post #4 of 22 (permalink) Old 12-29-2014, 09:50 PM
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Quote:
Originally Posted by Noodles View Post
It does sound like a caliper issue to me also.

It may just be the sliding pins needing to be cleaned up and greased well.
Good point. I recall now that my brake shop gave me several little packets of special grease to use on the pins.
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post #5 of 22 (permalink) Old 12-29-2014, 11:43 PM
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That is good stuff. I am glad you mentioned it because it should be brake grease not just any grease.
Also good advice about keeping the fluid clean. I do it at also at 24 month intervals regardless of mileage driven.
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post #6 of 22 (permalink) Old 12-30-2014, 12:00 AM Thread Starter
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Originally Posted by LostInTime View Post
When I have replaced pads, they have not usually rubbed against the disk.

When they did rub against the disk, I treated it as a brake caliper problem. I removed the caliper and took it to my local brake shop. They removed the piston (compressed air) and polished it, cleaned out the fluid area of the caliper of gunk, and re-installed the piston. That restored the full travel of the piston and stopped the rubbing.

Have you been flushing your brake fluid every 24 months?

If not, your brake calipers may be mucked up.

Warped rotors can often be identified by a "pulsing" in brake pedal feel when braking.
Umm, no, never done flushing before. I actually wanted to change the fluid but the mechanic the process was painful and that I would never have the same brake as before after flushing, so I just stood away from it. But I understand that I need to get it done anyways.

I don't feel any vibration on the steering wheel when I apply brake, so yes, I also guess this is not a warped disc case.
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post #7 of 22 (permalink) Old 12-30-2014, 11:35 AM
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Wheel turning freely 90% and sticking on the remaining 10% has to be something on the rotor or not likely bearing.
Beside warp it can be material defect on the rotor. Is it new rotor, or the old one with new pads?
Brakes pads do have come clearance to rotor when no brake applied, but the clearance is minimal and hard to see with bare eye.
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post #8 of 22 (permalink) Old 12-30-2014, 01:06 PM Thread Starter
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The mileage is 91k km. The rotor is the one that came with the car. The brake pads are new.
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post #9 of 22 (permalink) Old 12-30-2014, 01:22 PM
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That is a lot of miles for a modern rotor.

The only way to rule out if it is warped is to a reputable shop use a tool they have to see if it is warped. If it is do not let them machine or grind the rotor. It needs to be replaced at that point. The other side must also be done.
As far your mechanic saying the brakes will never be the same I always get a better pedal feel after a bleed. On track days I will bleed the brakes 3-4 times a weekend depending on how demanding the track is on brakes and a spongy pedal goes back to rock hard after each bleed.
I honestly question your mechanic's reasoning behind telling you that you would never have the same feel to your brakes.
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post #10 of 22 (permalink) Old 12-30-2014, 03:01 PM
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A new set of rotors is cheap. Just replace them. They are due for replacement anyway. If they are original, they must have a significant "lip".

BTW, repair shops love "sending rotors to a machine shop" to be "turned".
They make more money then they do selling a new set of rotors. Just buy new.
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Last edited by LostInTime; 12-30-2014 at 03:08 PM.
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