View Full Version : Front Brake Groans/Moans

04-26-2004, 09:13 PM
I'm sure everyone has had front brakes that squeak and whine at high frequency as you're coming to a stop and applying light pressure, but what about groaning?

This is a low-pitched sound much like my car made before I replaced the rotors. (I'm hoping I do not have to do this on my K.)


04-26-2004, 10:05 PM
I've had good luck with using Disc Brake Quiet on the back of the pads. It provides a layer of rubbery stuff that keeps the pads from vibrating in the calipers.

Also, adding a little teeny bit of anti-sieze to the edges of the pads where they fit in the caliper can help keep the noise down.

You might try cleaning the calipers with brake cleaner too.

04-28-2004, 08:11 PM
I've tried several things to stop the squeaks and have given up on that.

Cleaning the pads with brake cleaner seems to have rid me of the groaning.

04-28-2004, 08:25 PM
Have you checked your pads? If they are worn out, they will start cutting grooves in your rotors which you will feel with your fingernail when drug across the rotor or that you can see. The rotors should be smooth and shiney. If you've got deep grooves, you may have ruined your rotors.

Noises from pads can come from a lot of things like sand, water, mud, etc on the rotors which get on the pads or just from the pads themselves. Noises per se don't mean your rotors are toast.

Hopefully you already knew all this, and if you do, scuse me for the lecture. I'm not really sure if you're asking how to stop the noise or what are signs of serious brake rotor problems.

05-06-2004, 10:24 PM
The pads were new so I wasn't worried about that.

I guess I was indirectly asking about how to tell if the rotors are needing replacing.

05-07-2004, 01:27 AM
Originally posted by Cuervo
The pads were new so I wasn't worried about that.

I guess I was indirectly asking about how to tell if the rotors are needing replacing.

Replacement? Reasons could be excessie grooving like Dave pointed out, warpage or being worn past the minimum thickness. I think the min. thickness is stamped on the disc carrier on Kbikes.

05-07-2004, 02:01 PM
I've always found it difficult to tell what "excessive grooving" is - and why that would (if we can define it) cause any extra brake noise.

Some grooving is normal on any disk, and it just takes a bit longer for your new brake pads to conform to the shape.. once they do you have a larger effective surface area than on a completely flat disk.

One downside of using rubber coatings on the rear of the pads will be a slightly softer feel to the brakes. The coating has to compress before the pad does any work.

If you have squeeling/groaning - you could try taking the pads out and refacing them with some 400 grit aluminum-oxide (ALOX) sandpaper on a piece of 1/4" plate glass (for flatness). You don't have to remove all the ridges in the pad - just any glazed looking parts - and try to keep the pad parallel to the glass plate so it doesn't get off at an angle. I"d also check that my caliper bolts are torqued correctly (fairly low number if I remember correctly - something like 21-25 lb/ft..)

Another simple way to get rid of squealing brakes is to use them harder - do some good stops from a high speed using the noisy brake and get into the brake so you can really feel it working. This will usually quiet them down for a while. If you stay more aggressive in your stopping - it's likely they won't start squealing again.

I've never been bothered by squealing - it's something most BMW brakes do "Loud Brakes Save Lives.." - I just wear my earplugs and it doesn't bother me at all.

Oh - the thickness spec on all K75's and all solid-mounted rotor K100's is 0.140"