Help me fix really crappy sounding brakes
June 25, 2006 5:02 PM   Subscribe

New bike has disk brakes that squeek, cry and grind. It sounds awful. How can I fix this?

It's a Giant Sedona with disk brakes. They work well, (good stopping power) but feel grindy.

Is this because they are new? Can I just buff the disks with emory paper or something?

Yes, it's warrented but it's just a bike, and I like to fix stuff. Any ideas?
posted by snsranch to Sports, Hobbies, & Recreation (12 answers total)
I would venture to guess that this is because they are new, but I am no expert on bikes. Have you tried breaking them in (no pun intended)? Maybe a good weekend of hard stops will wear the brakes down to a point where they are a little quieter.
posted by galimatias at 6:08 PM on June 25, 2006

What's a crying brake sound like?

Just make sure the pads are hitting in parallel and work 'em in I suppose
posted by RufusW at 6:10 PM on June 25, 2006

Toe In

When a brake shoe hits a moving rim, the pull of the rim causes the brake arm to flex a bit. If your brake shoes hit a stationary rim perfectly straight and squarely, the flex of the brake arm will cause the rear edge of the brake shoe to do the brunt of the work. The front edge of the shoe may not even be engaging the rim under hard braking.

Good practice in installing brake shoes is to "toe them in", so that the front part of the shoe hits the rim first. As the brake arm flexes under real braking, it will permit the whole surface of the brake shoe to engage the rim.

Toeing in of brake shoes can also reduce the annoying squeal some brakes make when in use.

Most newer brake shoes have special washers with curved surfaces to allow you to adjust the angle of the shoe to the rim. Older brakes relied on brute force, typically bending the brake arm with an adjustable wrench.
From Sheldon Brown, your one-stop 'How do I...' Cycling resource.
posted by Orb2069 at 6:27 PM on June 25, 2006

I did not know that - thank you :)

Unfortunately, I don't own a bike anymore, definitely not one with snazzy disc-brakes
posted by RufusW at 6:39 PM on June 25, 2006

Wups. Brain fart - Could somebody delete that big thing up there?

Disks just have to wear in.
posted by Orb2069 at 6:42 PM on June 25, 2006

Right Orb2069, good advice but no toe in or out with disks. (Good advice though.) This is my first try with disks on a bike.

And yes, I've been working these poor bastards. Lots of high speed, downhill braking. I'll continue to work them in though and see what happens.

Thanks folks. But back to burnishing/buffing the disks, should I just leave them alone?
posted by snsranch at 7:42 PM on June 25, 2006

This fixed the squeaky brakes on my TR6, it might also work on bike brakes.
posted by buggzzee23 at 8:06 PM on June 25, 2006

you might want to try changing your pads to ones that are made with a softer compound. i don't know which brand of brakes you use, but i can get a variety of oem and third-party brake pads for my old-school hydraulic hayes brakes.

i don't know how true this is, but i've heard that the oil from your fingers can 'contaminate' certain types of disc brake pads, causing them to squeak. this is supposedly solved by sanding the pads lightly, and cleaning the pads and rotors with rubbing alcohol, taking care not to touch them with your bare hands.

of course, your pads might also actually be worn out!
posted by the painkiller at 8:17 PM on June 25, 2006

Adding to the painkiller- If your brand of brakes have metal and non-metal pads available, use one of each on each disc. It was recommended to me by a pro team mechanic, and helped, but I'm not sure why....
posted by pgoes at 11:09 PM on June 25, 2006

FYI, a faint grinding sound is normal, as is a horrendous squeal when braking in the wet.

good advice but no toe in or out with disks.

There isn't separate toe-in/out per brake pad, but you do have to align ("true") the caliper unit with the disc. Look into this if your brakes still squeak after a break-in period (check the instructions for your model).

Also check if your disc isn't true (i.e it's warped or mounted imperfectly). Look at the disc edge-on, spin the wheel, and if you see more than 0.5mm of wobble then take the bike back to where you bought it.

but back to burnishing/buffing the disks, should I just leave them alone?

Not worth the effort, because at the microscopic level you won't smooth the surface in the exact direction of wear. Just break them in by using them.

oil from your fingers can 'contaminate' certain types of disc brake pads, causing them to squeak.

I don't know about exacerbating squeal, but oil from your skin on the disc certainly reduces braking power. The difference is noticeable but not enough to worry about, at least on my brakes (Avid 160mm mechanical.)

No need to sand the pads (again, braking alone will do the trick), just clean with some degreaser or detergent and rinse well with water.
posted by randomstriker at 11:49 PM on June 25, 2006

Oh yeah, also make sure the disc is fastened tightly enough to the hub. If, like most people, you're not good at guesstimating your hand strength, use a torque wrench. A loose disc is a safety hazard and will certainly make scary noises.
posted by randomstriker at 11:56 PM on June 25, 2006

Hey thanks everyone. It all makes sense to me. But I never even thought to check to see if it was even set up properly. I'll check alignments and tightnesses before my next ride.
posted by snsranch at 4:49 PM on June 26, 2006

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