Brake Noise
 

When I apply either the front or back caliper brake on my road bike I get a "knocking' or "tapping" noise not unlike a bike computer sensor hitting the magnet. Unfortunately, that is not the problem. Usually the brakes must be used for a while to have the noise start. Once the noise starts it can occur every time the brakes are applied on a ride of twenty miles or more but not when I transport the bike to my my mechanic by car after the ride. Frustrating! The brake pads are in good condition. The wheels are Campy Euros and the calipers Campy as well. The wheels are not out of true. The bike is eight months old. The noise has been occuring for one month.

Bill

The pads are most likely hitting the seam where the ends of the rim are joined together.

Why would that just start now after seven months of not being a problem? Also, I believe Campy rims have welded and ground seams so they shouldn't be subject to misalignment.

To the OP: You say this happens using both brakes and both wheels? Have you tried braking with one wheel at a time to see if it's one, or both?

Quick things to check: Are the brake retaining nuts tight so the calipers can't move fore and aft? Are the brake pad holders tight on the caliper arms and the pads securely in the holders? Is the headset adjusted properly?

The noise occurs when either brake is used and, of course, when both are used together.

And the headset is brand new.

Maybe the rim wear indicator is making the noise?

But is it adjusted correctly? You said the problem has been happening for about a month... when did the new headset get installed? If the headset is loose, it could very well knock when braking. Even brand new headsets can do this because they need to be set up properly when they are installed.

Since it happens with either brake, it isn't likely the wheels or calipers.

The problem occurred prior to the new head set. My mechanic found the headset that was standard equipment in the bike (Bianchi L'Una 2005) needed replacement. The noise problem continued after this installation. The bike has been ridden only once since this was installed.

A seven month old headset bad? That's suspicious in and of itself. Maybe your mechanic can't adjust a headset properly. If you lock up the brakes stand over the bike and rock it back and forth, can you reproduce the knock?

My mechanic has the bike. Assuming I can reproduce the noise doing what you suggest, does that isolate the problem to the headset? If there is no noise, does that eliminate the headset? My mechanic has been focusing so far on the wheels. I have questioned this approach but find it difficult to discuss cycle mechanics since I know very little about the subject. However, your suggestion that wheels and calipers are unlikely sources seems logical to me. For one thing, how could new equipment on both ends of a bike go bad virtually simultaneously. Interestingly, there is another person in my bike club with the identical problem. She has been unable to find a soultion, though I don't think she has done anything more than ask other club members what it might be.

If you can't make it knock this way, it isn't a loose headset. If you can make it knock this way, the likelihood is that it's a loose headset although brake calipers can knock too. What you're looking for is play in the headset bearings.

One other thing, is it a rhythmic noise that cycles with wheel rotation or does it just happen once when the brakes are applied and maybe again when released? if it's the former, then it won't be the headset. If the latter, it's more evidence of a loose headset.

It is probably not the headset then. The noise is definitely rythmic, cycling with wheel rotation. That's why my first posting suggested it sounds like the computer sensor striking the magnet. It does not occur except when the brakes are applied; when the brakes are released the noise ceases. The noise ossurs whether I am peddling and applying the brakes or coasting and applying them. The bike must be pedaled for varying amounts of time for the noise to start. Sometinmes it is only after a few minutes of riding and other times after 10 or 15 minutes but it never fails to start - and it gets louder as the ride progresses - except on the short spins around the parking lot when I take it to my mechanic.

are these new brake pads? I changed over pads once and experienced the same problem.....

They are original equipment and have about 1900 miles of use. My mechanic says they look to be in good condition and my opinion is that he is correct.

I would still look in to the headset thing just in case.

The way I would check the headset is to sit on the bike, and lock up the front brake (only) and rock the bike forward and back fairly hard. If the headset doesn't knock using that method, you don't have a headset problem. Also, using the rear brake alone could cause noise if the headset is really loose, but headset problems should have much more effect on the front brake.

Make sure the bolts holding your brake calipers are tight enough.

Also, if your wheel bearings are loose, it could have a similar effect to a loose headset. (Braking could be a bit uneven and noisy.)

You say the wheels are not out of true. That probably means they've been checked for being out of round as well, but the problem you're describing could be the result of out-of-round wheels.

I'm assuming there aren't any visible dents in the rims if you look carefully. I've messed up rims by hitting bumps with underinflated tires, and it can cause knocking while braking. The solution is a new rim. (or to accept the funky braking.)

I certainly don't know what's causing your noise, but you seem to be absolutely positive it has something to do with your brakes, right? Well, you've probably checked this, but if not give it a look. When the noise starts, pull over and dismount. While taking a careful look at the two front brake caliper arms, slowly sqweeze tha brake lever. Determine if the brake arms & pads are contacting the wheel rim at the same time. I'd guess that most people over look this adjustment. If it's bad enough, your brakes could easily be pushing your wheel off center by as much as a quarter inch. Your wheel rim should never deflect to one side or the other when applying the brake. The only thing is, I've never had this issue cause noise. But, it's one of the things that you can easily check and adjust.

I can't explain why this is occurring on both front and back, but I had the exact same symptoms on my front brake only. In addtion to some of the checks already mentioned, I gave the rim a very thorough cleaning with alcohol and cleaned and roughed up the brake pad surface. Note that this didn't work the first time, so I filed more off the pads...and this time it fixed the problem. Apparently there was one point on the rim that the pad was "grabbing" differently causing exactly the noise you describe with each revolution.

Thanks to everyone who offered advice. My mechanic quickly found the prioblem once he had the opportunity to ride the bike for a few miles and heard the noise. The prize goes to Hillrider. It was the pads hitting the seams.

I believe that I was the one who suggested the seams.

You're right! Sorry, and thanks!

My LBS guy told me I should replace my brake pads periodically, whether they are worn or not. Over time, the pads become hard and brittle, and don't grip the rims as they should.