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At wit's end: XT brakes squealing when wet

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DrewBird

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Discussion starter · #1 ·
My XT M785 brakes squeal like crazy when wet. I thought this might just be contamination, but I've now changed up both rotors and pads, and the squealing continues. I was careful to bed these in properly; 10+ hard stops. They work flawlessly when dry, and are plenty powerful in the wet just quite loud.

Any ideas? I've ridden with buddies running the same brakes and they're quiet.
 
#9 ·
spyghost said:
contaminated pads. replace them and sandpaper the rotors
Click to expand...
Did you not read the OP??? :p

he just changed pads and rotors and still doing it, because its pretty normal. Ive used a few different brands of rotors, few brands of pads, couple brands of brakes. Every single one squealed to some extent when wet. Has nothing to do with contamination.
 
#13 ·
Some brakes on some bikes will make noise. I think it's when you change the frictional properties of the pads like getting them wet so their slip-stick squeal producing behavior hits the resonance of the frame and you get what you have here. You can always change the rotors. Larger rotors should change the Fs a little, maybe enough to stop this from happening. Shimano resin pads are very good pads. They're not like most resins that wear out quickly and have little power. They're on par with the metal pads in the power department and not far behind in the wear department.

All setups will make noise at some pressure and rotor speed. Mine will do it when I'm barely pushing the bike, maybe 1mph at most and I very lightly apply the brakes. I can make them make noise on purpose but it never happens when riding. Too much power and it won't make the noise and too little and it won't make the noise. What the water has done is it's made the pad hit that slip-stick (it changed the dynamic vs static friction) up to a rotor speed and pad pressure where it's noticeable. My resin pads have never made noise when wet except for very low speeds and light lever pressure. You might give finned resin pads a try. And make sure all brake mounting hardware is tight and the rotors are tight.

You might pull the pads and look at the friction surface. Make sure the caliper alignment is ok and that they're bedded in reasonably well. If the entire surface is not touching the rotor, they will be extremely loud and power will suffer. If the entire pad surface is being used, including no low or high spots, they're bedded in just fine. Metal pads can take a long time to bed in if the caliper is not perfectly aligned. The better aligned it is, the quicker the pads are ready to go and the quieter the brakes will be under all conditions. It's the fact that they're fine when dry and only make noise when wet that make me think it's an unlucky pad/frame combo.
 
#14 ·
IME some pads squeal and some don't. Try resin pads they have been pretty quiet for me in the wet. My current pads squeal when wet, but quiet down after being applied for a bit. I had some that ere so bad I threw them out.
 
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#15 ·
I have an Avid brake and rotor on the front and a Hope brake and rotor on the back,I use sintered pads in the winter and organic in the summer,they both squeal when they get wet.

They are worset when its just cold,damp and foggy,after a few seconds of braking in the damp conditions they dry pretty quick and the squeal goes and comes back after ive been off the brakes for a few minutes lol.

Ive found the Muc-Off brake disc cleaner does reduce the squeal alot,its meant to "rehydrate" (!) the pads.I spray it on the disc and pads the night before a ride.
 
#16 ·
Resin pads squeal a lot less than metallic ones. You'll still get a chirp when they're wet but after a second or two they shut up.

Rotors are different too. I found Shimano ones quite noisy. I've used Avid HS1 and Formula rotors with Shimano brakes and both squeal less than Shimano rotors.
 
Discussion starter · #19 ·
Resin pads will be the next thing I try. I had avoided these because my understanding was that they wear quickly and lose power in the wet; I live in the PNW where long descents in wet conditions are the norm. But, if Shimano resin pads do OK in these conditions I'll give 'em a shot. (This is also a reason this drives me nuts, this time of year ALL my rides involve some wetness and therefore some squealing.)

As I said, the brakes work great (powerful and silent) when dry, and are plenty powerful when wet, just noisy.

Re: caliper alignment, I think they're aligned pretty well; I generally loosen the bolts a tad, squeeze the brakes and then tighten them back with the calipers gripping the disc.

I've noted that Shimano calipers don't have the little gimbal nuts that allow lateral tilting of the caliper, the way SRAM brakes do, and I think sometimes that alignment isn't perfect. Nothing I can think to do about it though...
 
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