Squealing, vibrating rear brake

steelo

My rear brake, Juicy 3, has started to screech/squeal loudly and the entire bike vibrates violently under braking. There's plenty of pad and the lever has good movement and contact, could it be the wheel bearings? I have checked for movement and there isn't any play as far as I can tell but it makes the rear brake almost unusable!

Any suggestions as to what it could be or what I should be checking?!?

steve_sordy

Check that there is no air in the system by pumping the brake lever and checking to see that the lever does not go from soft to firm, or firmer. If so, the brake needs bleeding.
Check that there are no loose bolts anywhere (caliper, axle or Q/R). If so, tighten them to the correct torque. After that it must be the brakes themselves.

Following the elimination of air and loose fixings, I would suspect that the pads have become contaminated. You may have ridden through something and it splashed up, or if the bike was being transported on the car, it may have been splashed there . It may have been you of course when you were lubing the chain, or the mech.

It sounds bad, so I'd put the pads to one side and clean the disc and caliper with iso-propyl alcohol (IPA). Fit some new pads and bed them in. If that sorts the problem, throw the old pads away.

If you would prefer to try the disco inferno, that may work. Remove pads and place on a concrete or flame proof surface outside. Tip some IPA on to the pad surface, enough to just cover the surface. Then one at a time, direct a gas jet on to the pad. Heat until the edges of the pad material start to glow. You should see black smoke coming off, then flame. When the flame stops, the pad is done. Repeat for the other pad. When cool, put a piece of 100-120 grit sand paper onto a flat surface and in a circular motion rub the pads over the sandpaper. Keep stopping to blow off the dirty dust. The sanding process should only take 10-15 seconds per pad. Clean the discs with IPA then refit the pads and bed them in.

The Rookie

A common cause of vibration is contamination on the disc so the pads slip/grip repeatedly.

Brakes needing bleeding will not cause a vibration.

steve_sordy

The Rookie said:

A common cause of vibration is contamination on the disc so the pads slip/grip repeatedly.

Brakes needing bleeding will not cause a vibration.

The reason I mentioned the bit of advice about bleeding was that I once had a serious case of rear brake howl accompanied by vibration that shook the bike. I couldn't fix it, no advice given to me (and I followed it all) fixed it either. So, when all the bolts are tight, the pads are new and the disc has been degreased and sanded, frame alignment checked, caliper mounts refaced, and it still judders, what next? A thorough bleed fixed the problem. Why didn't I do that earlier? Because there were no symptoms of it needing one. My theory was that a small air pocket trapped somewhere very particular was acting as an air spring. I have never had this problem before or since. Three different bike shops, the emergency guy in the Alps and even the Kona tech guy failed to fix it. When I was coming down the mountain it sounded like I had a car horn. By the time I had bought multiple sets of pads, degreaser, sandpaper, LBS bills etc, it would have been cheaper to have thrown away the whole brake system and bought a fresh set.

Once it was fixed I sold the bike. I'd had it almost three years and I was ready for a new one. Instead of selling it whole I dismantled it and sold all the parts separately, keeping some for my other bike.