Written by Erik West Tuesday, 11 July 2006 12:08
If your bike lets out a loud wail when you put on your brakes, you are not alone. Usually this is a simple problem to fix too. The reason most brakes squeal is because the pads are not contacting the rim at the proper angle. This is also referred to as having incorrect "Toe-in". Most mountain bikes can have the toe-in adjusted. Many bikes can't be adjusted the usual way and resort to using a file or bending the brake arms. Read on to see where your bike fits in.
First, lets get the terminology straight and then we can walk through fixing the problem.
Toe-in: The angle that the rubber brake pad contacts the rim of the wheel when the brakes are applied. It can be: flat, correct toe-in or reverse toe-in. Flat is when the whole brake pad hits the rim at once. Correct toe-in is when the leading edge of the brake pad hits first. Reverse toe-in is when the trailing edge hits first.
Rim: The part of the wheel that holds the tire and the spokes. Usually made of aluminum, steel, plastic or carbon fiber. It's the part that gets squished by the brake pads.
Brake Pad: The rubber part of the brake that actually hits the rim and eventually wears out. Sometimes the pad is separate from the pad holder and sometimes it is molded into one piece.
Brake Arm: The two metal arms of the brake that the brake pads clamp to. They connect the brake pads to the bike frame and the brake cable.
Ok, with that out of the way, lets get down to business. The usual problem is the toe-in. Proper toe-in is when the tip of the brake pad that is closest to the front of the bike (the leading edge), hits the rim first, when the brakes are applied. It is a very slight angle because as you squeeze the brake lever, the leading edge hits and then the rest of the pad is squished up against the rim too. You want the leading edge to hit first. You don't want the leading edge to be the only part that hits. The trailing edge of the pad should be about 1 - 2 mm away from the rim as the leading edge begins to make contact. Take a look at your bike and see what's happening as you apply the brakes. Do it slowly several times to make sure you are seeing it correctly. It is a subtle adjustment.
Most likely, your brakes are hitting flat. As the pads wear down, they will eventually hit flat and need to be toed-in again. For most brakes this is simply a matter of loosening the bolt that holds the pads on and moving the pad in the proper place and then tightening it back down. Be careful though, because the pad will move in every-which-way and you can tighten it down in a worse position than you found it. If you follow these rules, you should be fine. But, some bikes have pads that can't be adjusted. If that is the case, read this whole article, but then follow the second set of steps below.
1. Make sure your wheels are centered in the frame or fork.
2. When you loosen up the brake pads, do one side at a time.
3. See how much pad is left. You may need to get new ones and this is a good time to do it.
4. When you put the pad back on, make sure it hits ONLY the rim and not the tire. Make sure it doesn't hit below the rim, toward the spokes. Make sure you tighten it up so the leading edge hits first.
This is easier said than done for the first few times. To get the right toe-in, I put a match- book cover under the back of the brake pad and then squeeze the brake lever to push the pad against the rim, catching the match book under the rear edge of the pad. This tilts it out to the right angle. Some new pads have a built-in "toe-guage" in the trailing edge of the pad to do the same thing. If it is built-in, don't bother with the match book.
Before you go further, try this:
· Wipe off the black gunk on your rim. Use a little steel wool, fine sandpaper or a rag. See if that solved the problem. It often does.
· Take a file and file the shiny part off your brake pads. That often quiets them down. Make sure you check the toe-in before and after you do it. It still needs to be toed-in properly.
If these didn't help, continue.
Steps for adjustable brake pads:
1. Loosen up the brake pad but don't take it off completely. Put a few drops of oil on the nuts and washers and wiggle them around to get it on all the surfaces. DON'T get the oil on the part of the pad that hits the rim. (If you do, just wipe it off. No biggie.)
2. If you have a used or otherwise flat pad, put a match-book cover under the trailing-edge of the pad. Slowly squeeze the brake lever to put the brakes on. Watch the pad to make sure it doesn't violate rule #4 above.
3. Be patient. It will take many tries to get it just right. Wiggle the pad around until you have it in the right position. Then slowly tighten the nut or bolt to lock it in place. It may twist out of line as you tighten it. That's OK. Just try it again. You may need to have someone else squeeze the brakes while you hold the pad and tighten the bolt at the same time.
Steps for non-adjustable brake pads:
1. Make sure the pad is in good condition.
2. If the brakes are on nice quality brakes, use a file to cut the angle you need into the rubber of the brake pad. This usually does the trick.
3. If your brakes are BMX brakes or not super high quality, you are left to the old-school method of bending the brake arms to give you the toe in. Try using an adjustable wrench on the arm to bend them how you need to. Don't bend them too much because you can effect their integrity if you go to far. Aluminum is especially prone to cracking if bent several times. This method is ugly but it has been used for many years successfully.
Final tips of the trade:
· Steel or chrome plated rims love to squeal and don't let your bike stop very well no matter what you do.
· Wet rims like to squeal no matter what also.
· Brake arms that are wimpy and flexy or have too much play in them will also like to squeal. If they have too much play, they will make the toe-in procedure nearly impossible because they move in ways they shouldn't. Time to upgrade.
· Buy pads with replaceable rubber "brake shoes". Linear pull, otherwise known as "V-brakes" use ultra thin pads that are nearly worn out from the day you by them. You will replace these often. Replaceable shoes are cheaper in the long run.
· In worst-case squeal problems getting the pad dirty actually helps. I've used soda, grape jelly, and even oil, in small quantities on the rim to make the brakes shut-up. I've also had all these methods make things worse or just make a mess. In a few cases, reverse toe of the brakes actually helped too. Don't ask me why.
*This repair article was written by Erik West of The Bicycle Workshop. The Bicycle Workshop teaches repair and riding classes in Maine.
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