[willevans]

I've got a lot of noise coming from my rear wheel and frame under braking. It sounds like Gilbert Godfree gargling nails with a megaphone. It's just started happening three or four rides ago and there haven't been any equipment changes to inspire these new noises. It's not a squeal or a squeak, but an unholy ringing/groaning with vibrations that I can feel through my feet. It starts as a high-pitched ringing and builds with volume and even sounds like all the spokes are vibrating with it.

I've swapped out between three different rotors to make the noise go away and was unsuccessful (Shimano 6-bolt Doere-level, Mugura Storm SL, and Avid G2, all 160 mm). I also switched pads from metallic to resin. I also put noise damping paste on the back of the pads. Going through all these iterations systematically I managed to waste most of a Sunday. No change in the pitch or tone from Gilbert.

The more I think about it, the more I think the cassette is playing a big role in responding to the vibrations under braking and amplifying them. The problem is I've checked the cassette and it's tight to the freehub, but the freehub has a little bit of play in it. The wheelset is in good shape, but easily has 400 miles on it, all on dusty Southeastern trails. I think that a freehub replacement might be what is needed. There is a little play, but not enough for me to really measure. Also, the axle spins smoothly without play or binding so I think I can eliminate the axle as a contributor.

Before I spend any more money I wanted to check with you guys if you've had trouble with the stock 495/505 Shimano calipers that come stock on a 2011 XTC 1. Again, the bike was dead silent under operation until just a few rides ago, and with no equipment changes, I'm lead to believe that something has worn enough to allow this vibration to creep in.

What do you guys think?

 

[bassman1441]

I have/had the same problem on my 09' trance x3. The vibration I used to have happened as the frame flexed slightly under hard breaking causing the caliper body to hit the arms of the rotor.
Right now I just have a vibration that I can feel in the bike and hear but its much different in that the rotor arms aren't hitting the caliper anymore and it pretty much just a typical break noise.

If there are scratches on the rotor arms and not just on the braking surface then there's a pretty good sign that you had the same problem as me. If that's the case just realign the caliper

 

[willevans]

I should have mentioned I realigned the caliper and the noise persists.

 

[bassman1441]

If your having the same problem I did realigning the caliper should have fixed unless the frame is flexing a lot, but it sounds like that may not be the case.

Organic brake pads seem to solve a lot of brake noise and vibrations so you could try some of them on your rear brake.

 

[willevans]

If your having the same problem I did realigning the caliper should have fixed unless the frame is flexing a lot, but it sounds like that may not be the case.

Organic brake pads seem to solve a lot of brake noise and vibrations so you could try some of them on your rear brake.

If it was frame flex then the bike should have made this noise from the beginning, right? The bike has been dead silent the first 400 miles and then within one ride became a noisy mess.

Also, I mentioned above that I have subbed out the metallic pads with organic with no change in noise.

 

[eshaheen]

I'd imagine there is something more going on here, but mine frequently do this as rubbing alcohol fixes it. I chalk it up to the dusty trails in dry Texas right now.

 

[bassman1441]

If it was frame flex then the bike should have made this noise from the beginning, right? The bike has been dead silent the first 400 miles and then within one ride became a noisy mess.

Also, I mentioned above that I have subbed out the metallic pads with organic with no change in noise.

Opps forgot that you said you did that in your first post.

Try cleaning the rotors as eshaheen mentioned and try some new brake pads in case the rotors and pads were contaminated. Sometimes it also works to file some of the pad off if it wasn't contaminated too badly. Contamination is known to cause all sorts of brake noise/problems.

Also good point on the frame flex. However the problem I used to have started after I realigned the caliper to eliminate brake rub, the caliper hit the rotor arms because I moved the caliper farther to the inside of the bike and then I fixed it by moving it farther to the outside of the bike. The frame flexed from the beginning as expected but the caliper was in a different position.
But it doesn't sound like you did anything that would cause a problem like I had, so contamination is my best guess.

 

[willevans]

Okay Guys,

The prevailing idea is that somehow the pads or the rotor or now both have been contaminated and I need to take out the pads and rotor to address the issue.

Would spraying down the pads and rotor with brake cleaner help (the kind you get in the big spray cans from the auto parts store)? I'm also thinking about putting a camfer on the edge of the pad that is opposite of the direction of rotation to see if it works for disc the way it works for rim pads, but I'll clean everything again and test that first.

 

[bassman1441]

I've heard that using brake cleaner isn't ideal because it can leave a residue on the pads and rotors but haven't tried it myself so I can't say for sure. Rubbing alcohol won't leave anything behind and seams to work pretty good at cleaning so I would start with that. After you clean the rotors make sure to file down some of the pad so that any contamination is removed from it so you don't re-contaminate the rotors

Also putting a camfered edge on the brake pad sounds like it should help and it shouldn't cause any problems. Good luck.

 

[willevans]

I found out what the problem is.

After doing a long ride with several long downhills and deafening noise under braking I examined the rear caliper and saw something new for the first time. The rotor was machining away bits of the caliper.

The outside piston had frozen in place and the inside piston was pushing the rotor into the caliper. It was hard to diagnose because of the shape of the rear rotor and the angle it hit the caliper at made the brake pads remove all evidence of rubbing from the rotor, and hid the evidence (the silver bare metal showing) on the caliper. I took the wheel off to try cleaning the caliper again and saw bare metal for the first time last Saturday.

I shimmed the outside brake pad towards the center of the caliper and did a few more hard stops and the noise was gone, so that seems to have taken care of the noise...for now.

The bike is less than one year old so I'm taking it back to the shop for warranty work. I'm posting here to let everyone know that if the noise is particularly awful, it may be much more serious than the pads vibrating or contamination.

 

[bassman1441]

That's the same problem I had, but I guess I forgot to include that one of the pistons was stuck on my caliper too.