How does one remove carbon deposits on a brake disc (rear)? I have one rear brake disc that keeps squealing with the brakes applied. It's is not the pads, there is plenty of meat on them.
Ideas?

Thanks

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member

I am puzzled by your assumption that there is carbon building up on the disc. I've never seen a disk with carbon build up. Squealing usually has to do with the pad composition in my experience, although there are often shims and/or paste specified to reduce brake squeal. Assuming you used the recommended paste etc. I would suspect the pad compound.

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'97 E 300 D

I have always solved that problem with a bit of antisieze on the back of the pads.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

I don't care if my brakes squeal as long as they stop the vehicle.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.

The squealing is caused by the vibration of the metal backing of the pad. You can have plenty of material on the pad and you can have new rotors while still having squeal. Most shops put anti-squeal paste on the backing plate of the pad before installation - Mercedes are notorious for this issue. Go to the parts store, get some anti-squeal paste, remove pads, cover the metal backing plate entirely with a thin layer of the stuff, then put it back together.

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- Brian


1989 500SEL Euro
1966 250SE Cabriolet
1958 BMW Isetta 600

Nelbur, I say carbon build up because I had previously looked at the brake disc and there was a build up of a dark gray substance on the disc. that just would not scrap off. I just presume this is causing the squeal. I do have some anti-squeal grease and will apply it to the pads and see what happens. I suppose I could take the brake disc to a shop and have them mill this build up, off.

__________________
1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member

Just make sure you apply it to the backing plate and not the pad. Sounds as if either someone contaminated the pad material at one time or wore a set of pads down to the backing plate

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have no worries.....President Obama swears "If you like your gun, you can keep it

Ya, something got built up or baked onto the disc. You can feel it. I will be sure to keep the paste on the backing plate.

__________________
1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member

Now that is odd. Have you tried brake parts cleaner?

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.

I was taught to every once awhile to slam brakes hard to remove glazing on rotors.learned from british leyland,Jag,and Jensen's

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt

Generally pad material transfer to the rotor is desirable, it increases the friction coefficient and is partly why new brakes on fresh rotors don't work so well at first.

There is a chance that the last set of pads had a material that is incomparable with the newer pads but there really isn't a way to tell. Some 80 grit sand paper could be used to clean both sides of the rotor, don't expect to get much of an even looking surface, it will be lots of work. Hard brake material can also make noise.

Pad shims are usually coated aluminum to prevent squeaking between the pad back and caliper piston.

If there are outlines of the brake pad around the rotor, this is sign of repeated hard brake use then sitting stationary for a period of time. ( running road course time trails, coming off the track hot then parking the car.) This might cause noise but usually results in thumping when the brakes are applied.

Sometimes the caliper does not have enough mass damping and will squeak no matter what you do. I've read that on the R129 bodied SL600 aluminum calipers were prone to noise at more than 1/2 pad wear, moving to steel calipers added more mass and took the system out of resonance. It might be worth looking for a service bulletin.

I didn't know that. And I have an ASE brake cert. Learn something new every day

I've seen those outlines before. I thought that might be the cause.

Interesting. I'd be less interested in adding unsprung weight, but also curious how well aluminum calipers stand up to heat over time. Come to think of it, the calipers on my bike are probably aluminum, but that's with large dual front rotors, plenty of air flow, and only about 600 lbs of combined bike and rider to slow down.

Good post!

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.

In the past I tried using both brake cleaner and a wire brush and thought I had it licked. However the brake squeal has returned. I will be finishing up some ignition work on my friend's car on Friday, so I will try the heavy grit sandpaper approach.

__________________
1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member