Disc Brake Noise - an Important Discovery?

thedktor · June 2007

My Stumpjumper is going back to the shop today as the brake noise is just too annoying.

Did lots of fiddling over the weekend and I think I know what causes it, or at least contributes to it. I would be interested in others opinions/experiences.

Basically , the pistons don't move evenly, and on both front and back callipers, one piston produces much more force than the other.

This was unchanged after working the weaker piston numerous times with the other clamped still.

So, the result of this is that one pad will push against the disk, while the other one has less pressure and is so free to vibrate and squeak or squawk. Also, the disk bends slightly as well from the stronger piston which may in itself cause noise.

After working the weaker piston probably 50 times the situation was no better, so hence back to the shop. I really don't think there is air in there, but the shop can look into that.

Interestingly (perhaps) it is opposite pistons that are "sticky" front and back, so its not obviously air in the bleed side or whatever.

This is really frustrating me as the bike is just so good in every other respect, but I don't feel enthusiastic to ride it cos of the awful noises it makes!

TD

Mad Splasherwmb · June 2007

This happens with every brake. It's impossible to get the friction between both pistons exactly the same so one piston will always touch first. However, the brake force you get is almost negligible until the second piston makes contact and that's when your noise will start.

Noise can be caused by all sorts of things but misaligned mounts and contamination of the friction pair are the most common.

I recently couldn't stop an HFX9 squeeling after an upgrade to a bigger rotor. Finally changed the pads from sintered to organic (having tried new sintered on the way) and it's fine (and the stopping power is awesome).

George
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thedktor · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Mad Splasher

This happens with every brake. It's impossible to get the friction between both pistons exactly the same so one piston will always touch first. However, the brake force you get is almost negligible until the second piston makes contact and that's when your noise will start.

<hr height="1" noshade id="quote"></blockquote id="quote">

Yes completely agree there Mad.

But in my case at least, one piston is MUCH more powerful on both front and rear callipers.

I could not actually stop the stronger piston moving, despite considerable force, while trying to get the weaker piston to move and loosen up.

so something is not right, either air in the system, faulty (sticky) seals, or the design of the calliper internals doesn't balance the hydraulic force properly.

I am hoping that if the 2 pistons can work more evenly then noise will be reduced. Hoping being the word ....

TD

Hole Nut · June 2007

I use Hope Enduros and they have a reputation for being the squeeliest, but personnaly I don't have a problem with them. In the arly days I'd just give them a squirt with disc brake cleaner just before riding off. I'd apply the brakes a few times just to build up some heat to evaporate the solvents then they'd be no hassle at all but for ageas now I just "go and wash after"
Yes I agree that one pad will sem to work before the other thats just normal, Historisys (not sure of spelling but the word is right) the slang for it is stiction (sticky friction)
Just make sure the disc runs exactly equal distance between the caliper using feeler guages, then insert your pads. perhaps put a bit of copperslip on the backs of the pads, although this will just wash off in time.

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Santa Cruz Heckler
Specialized Allez Comp
(sold my BMX)

Disc Brake Noise - an Important Discovery?

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