kyleputzier

The rear disc brake on my bicycle makes noise only at very slow speeds, as when coming to a stop. It is a much deeper sound than the usual squeal heard at higher speeds. Don't know exactly what this issue is called. Maybe judder?
The front brake does not make noise.

Original pads were semi-metalic. Current pads are resin.
Pads don't rub and retract as expected. Pad alignment has been adjusted and seems to be OK.
Rotors cleaned, pads resurfaced.

What are the other possible causes of this issue?

Kyle
Trek FX Sport 4
Stock Promax DSK-927 hydraulic disc
Shimano XT rotors

Andrew R Stewart 

What type of noise? For us to help we need to know.

Squeals and moans are from a vibration which has such a short cycle that we can't hear the quiet between the loud points. Shudder is when one can. Look at the rate of wheel rotation and how quickly the disk's cutouts/slots/holes pass by the pads. How many pulses per wheel rotation?

We have solved some of these noises by replacing the disk with one with a different brake track cooling cutout shape/pattern. Andy

kyleputzier

It's difficult to explain the sound, even though I imagine it is fairly common. I seems like the brake is, very quickly, grabbing the disc, then slipping, then grabbing, then slipping . . .
I though maybe the disc was not tight, but it is OK.

Kyle

mpetry912 

ok so first, make sure the 6 disk fixing bolts (if ISO) or lock ring (if center lock) are tight.

then loosen the caliper bolts (to the frame) pump the lever a couple times, put a rubber band around the lever, and tighten the caliiper to ensure that it is aligned to the disk.

then last thing find a big-@$$ hill and drag the brake going down to generate some heat and bed the pads in

on automotive disk brakes, there's the concept of "green" pads that are freshly installed out of the box and have poor braking characteristics. The friction material needs to go through several heat cycles before they show really good braking performance.

anyway try those 3 things and report back please

/markp

kyleputzier

ok so first, make sure the 6 disk fixing bolts (if ISO) or lock ring (if center lock) are tight.
Center lock disc is tight.

then loosen the caliper bolts (to the frame) pump the lever a couple times, put a rubber band around the lever, and tighten the caliiper to ensure that it is aligned to the disk.
Did that. I've gotten pretty good at aligning he calipers.

then last thing find a big-@$$ hill and drag the brake going down to generate some heat and bed the pads in
I didn't find a big @$$ hill, but I did bed in the pads by going fast and stopping quickly (while not actually coming to a full stop) 10...15 times.

mpetry912 

and ... same result ? still has this "judder". I'd say try different pads is the next step ?

/markp

oldwinger14

What the initial posting described is what I experienced the past two weeks. My front brake would make no noise until I was almost at a stop and the brake lever was squeezed tightly. Then, the brake would make a very loud screeching-type noise. I loosened the caliper and squeezed the brake lever to, hopefully, center the rotor between the brake pads hoping to solve the problem. I did that a few times before accepting that was not the solution. When hat didn’t work, I started thinking I may have a problem with the piston in the caliper not extending out far enough to make the brake pad fully press against the rotor. Rather than pulling the caliper apart myself, with no guarantee that would solve my problem, I took my bike to my local shop. I explained the symptoms and what I had done to date. I left the bike and awaited their call. Before I arrived home, I got a call saying the front pads needed replacing, as they were scored and quite worn down. They installed new front pads and my problem as solved.

Pop N Wood

Rotors can get an uneven layer of pad material on them, causing them to grab differently as the rotor turns. Makes the braking power pulse leading to noise and vibration,

Keeping everything clean helps. Scrubbing rotors with a scotch bright pad and brake cleaner often cleans them up. If it is really bad taking them off and hitting them with a sander returns them to as new condition. Just don't use sandpaper with any sort of metal oxides, as that can work into the stainless rotor causing rust. A garnet sandpaper for wood works quite well

I used to bed in brakes, both cars and bikes, but now don't see the point. The brakes seem to work as well with or without the bedding procedure. Just make sure you don't let the wheel stop turning once you get the bakes hot. Will cause the pads to literally melt into the rotor where they are parked.