Vibration when braking
 

Road bike with caliper style brakes. The brake pads have about 3000 miles on them, but still look good. My wheels, with KinLin XR-300 rims, are new, and have vibrated while braking since day one.

The vibration seems to be 2-3 times per wheel revolution, so it is most noticeable at high speed.

Any ideas?

I should add that the wheels are perfectly true, and that I have cleaned and lightly sanded the brake pads.

Wipe down the rim braking surface with rubbing alcohol. Check brakepads closely for imbedded debris. Brake pads may be toed in too far.

Your brakes are road calipers. U brakes are a completely different type of brake, much like a conventional cantilever (but different), mounted beneath the chainstays on mountain bikes. They were a flash in the pan, installed on mountain bikes in the very late '80's.

My guess regarding your vibration would be a loose headset(for front brake) or the brake is loose in the mount and needs to be tightened up.

Possible causes:

1. loose headset
2. loose wheel bearings
3. loose brake-caliper centre bolt
4. loose brake-caliper arms
5. rim-width not consistent all the way around, although this is more likely with an old beat-up bike. The telltale sign of this is the frequency of the shuddering occurs once per wheel-revolution, usually around the seam area.

What sort of brake pads? I had a similar problem with Kool-Stop salmon pads which went away when I installed Kool-Stop black pads. After the rim wore in, I put the salmon pads back on and they worked great.

They're Shimano pads. They've been on the bike for a while, but the wheels are new, and when I changed the wheels I started noticing the vibration.

Use schochbrite (red) to clean the rim's braking surfaces and brake pads. Check trueness of rim with a dial gauge. A 0.010" "blimp" is noticeable with light braking around +15 mph. You may have several blimps on the rim (2-3x per revolution). Replace the pads if problem persists.

I'm assuming by "blimp" you mean a spot where the rim is wider. That's exactly what I have 3-4 spots around the rim appear to be about 0.2-0.25 mm wider than the other sections. Will replacing the pads help wear the rim evenly?

New pads will not cure vibration caused by "blimp". Remove wheel and tire from bike. Use plastic mallet to reduce "blimp". Put a 12" piece of wood against other side of the rim so you don't damage the other side of the rim.

harder black pads would smooth out any protrusions.