I searched on the SOHC4 forums and got some info for getting rid of that noise. Here's what I did:
- Put "disc brake quiet" on the back of the pads. It's a flexible material, kind of like caulk that's supposed to absorb vibration and reduce squeal.
- Checked the front wheel spokes for even tension. I "dinged" the spokes with a wrench and tighted up the loose ones.
- Cut a groove in the brake pads horizontally (level with the ground). The grooves went through the pad material to the metal backing. This is supposed to change the vibration harmonics of the pads.
- Beveled the leading edges of the brake pads at a 45 degree angle (the side of the pad that contacts the disc first, as the wheel rolls forward).
- Lightly sanded the brake disc to loosen up glaze from the brake pad material.
- Checked for the nylon washer on the piston-side. Oh, where did that go? I remember seeing a blue nylon washer the first time I took the brakes apart. It was gone.
All of the "fixes" above had not cured the brake squeal. It was so loud, it was annoying to use the brake, mainly as the bike was coming to a near halt. I bought a rubber O-ring and put it on the piston side. It may have reduced the noise a little. Next, I went back to the hardware store and found a large nylon washer.
There's a raised spot on the brake pad that the hole in the washer should surround. The hole was too small and I drilled it out to fit. Dimensions of the washer (after drilling) are 7/8" hole and 1 1/2" outside diameter, 1/8" thick. You can see the washer in the photo below (it's white). The purpose of the washer is to guide the brake pad, so it contacts the disc evenly when the brakes are applied. If one side of the brake pad contacts the disc before the other, supposedly it will make noise.
The washer cost 61 cents and has cured about 95% of the brake squealing problem. Another "fix" mentioned in the forums is to apply brake cleaner to the disc brake. It's supposed to remove grit and grease from the disc. I bought a can of brake cleaner at the hardware store for $3. It cleaned up the disc and made it shiny but I don't think it did anything for quieting the brake. Well , the nylon washer made such an improvement, the brakes are quite "liveable" now. It's fun to ride this bike - the brakes work and they're quiet!
Handy tools for this job: 14 mm socket, 8mm wrench for the brake bleeder and a clear hose to attach to the bleed nipple. Brake fluid may also be needed.
