View Full Version : Disc brake squeal

06-23-2015, 05:41 PM
So, I think I failed to bed in the brakes on my new MTB. I always just assumed they would bed in by themselves eventually but my research indicates that if you don't do this correctly at the start, you kind of screw up the rotor/pad interface.

It has < 100 miles on it, but a lot more trail/offroad than I would normally ride - probably >50%, and the brakes squeal a ton. I've read stuff online suggesting sanding the pads, and even putting the rotors in the dishwasher to remove contaminants. Suggestions?

06-23-2015, 06:00 PM
I have also heard you can grill them. I would probably get new pads if it were really bad and keep the current ones as spares.

First thing to try is just cleaning off the rotor. I use rubbing alcohol, but if you have brake cleaner that would probably work too! :-)

I have never bedded in rotors/pads on the mtb (but did on road bikes); they have never squealed much unless wet.

06-23-2015, 06:10 PM
have never squealed much unless wet.

I like to think of my disc brakes as an auxiliary fog horn when wet. I've had people in cars with the windows up jump at the noise when I stopped beside them.

06-23-2015, 06:19 PM
Mine have always squealed more or less. I've learned to modulate the brakes in such a way as to avoid it, and I almost never hear it now. When I want it to, I can get it to scream, which is kind of fun.

My research came up with varying reports about the importance of bedding in the pads, from "don't mess it up or else" to "just ride normally and it will be fine." I understand it's a bigger concern to avoid glazing them in the first few miles. There's Squeal Out disc brake paste, too; I almost tried it, but decided I didn't care enough.

06-23-2015, 10:47 PM
I have discs on my CX and beater MTB, never really bedded them in, and they don't squeal anything like this. They're horrendous even in dry conditions.

06-24-2015, 04:52 AM
Yeah, that doesn't sound nice. Try new pads! (Assuming rotor cleaning doesn't fix it.)

Harry Meatmotor
06-24-2015, 06:56 AM
Squeal out works like gangbusters. Just be sure to follow the instructions.

other than that, get a can of Brakleen from the autoparts store and liberally spray down the caliper (with the wheel removed!) and wipe down the rotor with a clean rag sprayed with Brakleen. Don't spray anywhere near the hub bearings!

Then, to bed the pads to the rotor, find a long-ish steep hill and do 5-10 long stops, braking "the wrong way" by applying constant moderate pressure - trying to get as much heat into the rotors as you can.

06-24-2015, 07:17 AM
Squeal is high frequency sticking and releasing. The frequency is normally a function of the flex in the brake rotor, caliper and mounting.

Might be worth the time to pull the pads out and sand the contact faces with 120 grit paper followed with a solvent cleaning. Then you can de glaze the rotors with a wet green scotch bright pad followed with a solvent cleaning. Pinch the wetted pad around the rotor and spin the wheel to cut the shine then use circular motion to leave a more random surface pattern. The pads will bed better when the rotors have some scuff to them.
Once everything is back together check the alinement of the caliper to the rotor and the pads make sure everything is torqued to spec.

Be carefu with brake cleaners. Some are harmful to paint! I found the Brake Kleen brand formula in the red can to be the least aggressive. Test it first!

06-24-2015, 08:06 AM
When I've had contaminated pads/squealing, I generally remove the rotors and hit each face with my 5" random orbit sander with 220 grit paper on it, then clean them with rubbing alcohol. Then remove the pads and do the same to the face of them (minus the alcohol). Then put it back together and do a few dozen hard stops and they generally work well.

I few years back I had seals fail on my DH fork and it leaked fork oil onto the front brake. This worked to rescue the rotor and (surprisingly) the pads too.

IME, certain models of rotor squeal more than others. The polygon rotors avid used for several years are awful. I have a few sets and just regard the squeal as my brakes saying "I'm an avid brake that is braking!".

06-24-2015, 09:18 AM
Also be sure the noise is actually coming from the brakes and not your shoulder joint. Just saying...

06-24-2015, 10:02 AM
Also be sure the noise is actually coming from the brakes and not your shoulder joint. Just saying...

I had a clicking sound on one of my prior bikes whenever I climbed a steep hill, and was relieved when I found it was my bottom bracket and not my right knee.

06-24-2015, 11:22 AM
Thanks for all the suggestions, folks. Sounds like I'll need some elbow grease whichever approach I take. Darn it.

06-24-2015, 11:44 AM
I have all the stuff you need to treat the brakes as well as a place to work if you need a hand

06-25-2015, 06:27 PM
I have all the stuff you need to treat the brakes as well as a place to work if you need a hand

Thanks! I am going to try the alcohol / sandpaper treatment first but if that doesn't work, I may take you up on your offer.

07-08-2015, 11:12 AM
If nothing is working for you, start looking at alignment issues. Is the caliper ever so slightly out of parallel with the rotor face? Are the pads not seated evenly in the caliper?

If all of the previously mentioned approaches don't solve your problem or only seem to solve it long term, seriously look into having your caliper mounting surfaces faced. I had a set of Juicy 7's and then Avid Exlir CR's that no matter what I did (most of the stuff mentioned previously in this thread in addition to multiple pad/rotor combinations), I couldn't get more than a couple of rides before I'd get a horrendous donkey squeal sound out of my brakes every time I used them. My last resort was to have the disc brake mounting points of the frame faced. Problem solved. Finally, and after a lot of cash and effort thrown at it.

These days I'm running XTR trails on both mtb's and BB7 roads on the commuter and road tandem. Every now and then something will contaminate the XTR pads and they will make all kinds of noise and loose all stopping power. I've tried everything in the book short of the dishwasher method mentioned, and the stopping power never returns on those. Pad replacement has been the only thing that works for me on the XTRs. My original contamination issue was due to damn near imperceptible leakage at the line fitting into the caliper. Replaced shimano lines and fittings with jagwire and have only contaminated pads twice since....once was because a gel leaked out of my pack and dripped all over the rear caliper. The other time was after a cross country flight (bike disassembled in the box and on the plane) that I still don't know the root cause of, but I did have to bleed the brakes as well after that flight.