Brake Mechanism

(M = mountain bike; R = road bike; C = cruiser)

DESCRIPTION: There are different kinds of brake mechanisms on the different kinds of bikes. Each paragraph below covers the mechanism for the type of bike in the paragraph flag at the beginning. If you have a hybrid bike, the brakes are probably like those on mountain bikes.

(M) Most mountain and hybrid mountain/city bikes have cantilever brakes. They have two pivots, one on each side of the wheel. The pivot bolts screw into mounts, which are usually brazed to the seat stays of the bike frame. > This means they are very simple, light, and strong, but if you bend or smash the pivot and mount, it takes major surgery to replace it.

2-8 Cantilever Brake

(M) Many newer mountain bikes have V-brake mechanisms. These are really just cantilever brakes with the cantilevers pointing straight up and a single cable pulling the arms together, instead of a main cable and a traverse cable. They are very simple and reliable mechanisms, even lighter than standard cantilevers, in some cases. One word of caution about V-brakes: use them gently. They work. You put them on, and the wheel tends to stop, RIGHT NOW. Also, most V-brake models require that the brake shoes sit very close to the wheel rim, even when the brake is fully released. So you have to keep the brakes adjusted carefully, and you have to keep your wheels straight so the rims don’t rub against those nearby brake shoes. If you have V-brakes on your bike, use the instructions in this chapter for cantilever brakes to do any adjustments and repairs. The only differences will be in the steps that deal with the cable, and dealing with the cable and anchor bolt on a V-brake is so simple it requires no additional explanation.

2-9 V-Brakes

(R) Most road bikes have side-pull brake mechanisms, or caliper brakes. The two arms, or calipers, pivot around one pivot bolt, and the brake cable pulls the arms together from one side. Some have two pivots, one for each caliper. These caliper mechanisms are time-tested, and if they are well-made, they can be light and strong. They don’t deliver quite as much braking power as similar-quality cantilever brakes, but for road riding, if they are used carefully (that means using both brakes, and using the front ones a bit more than the rear ones as you stop), they work just fine.

2-10 Side-pull or Caliper Brake

(C) Cruiser bikes and most children’s bikes, except the racey BMX models, have coaster or foot-powered brakes, with a mechanism inside the rear hub. They are usually trouble-free, but they can wear out. If you have problems with a coaster brake, try working a little oil into the hub from the sides, and if that doesn’t help, do a complete overhaul (discussed later).

PROBLEMS: (M, R) One-shoe drag. One of the brake shoes refuses to come off the rim of your wheel when you release the brakes. First check to make sure the wheel isn’t loose and/or cockeyed. Push the wheel all the way into its drop-out (fork-end slot) in the frame and tighten the quick-release or axle nuts firmly.

(M) Check the brake mechanism. If the carrier is the kind that the main cable passes through, as shown in Figure 2-8, loosen the secondary anchor bolt in the carrier, adjust the position of the carrier so the brakes center, then retighten the secondary anchor bolt.

(M) If the springs on the two sides of the brake are out of balance, on a cantilever or V-brake mechanism, fiddling with the transverse cable won’t solve the one-shoe drag; you have to adjust the springs. On most cantilever and V-brakes, there is a wee Allen bolt or Phillips screw that you can adjust to center the brakes. On some cantilever units, such as the Dia Compe 986 set, there is a pivot bolt that you can put an Allen key into, and a thin adjusting nut between the body of the cantilever and the bike frame. Fit a hub spanner or the thin jaws of a Cool Tool on this adjusting nut. Loosen the pivot bolt with your Allen key, then reset the position of the adjusting nut so the brakes are centered. Hold the nut in that position while you tighten the pivot bolt with the Allen key.

(M) On a few cantilever and V-brake models, you have to reset the spring on the cantilever of the dragging shoe. To do this, pull the removable end of the transverse cable out of its slot in one cantilever to loosen the brake, then loosen the pivot bolt for the dragging shoe cantilever about Five to seven turns. Then grasp the whole cantilever unit and slip it out on the pivot bolt, until the end of the spring end moves out of moves up to the next higher hole in the mount plate (there are usually three little holes, and you can often hook the spring in a notch at the top of the plate for one more extra-tight setting). Setting the spring tension this way is a pain; if you have a lot of trouble keeping your brake shoes centered, I recommend you switch to ones that are easy to adjust, like those with wee Allen bolts or Phillips screws.

(R) Check to see whether the whole brake mechanism is loose on its pivot bolt. If it’s loose, so that the whole thing waggles back and forth, and the tightening nut (see Fig. 2-11) turns freely, just tighten that nut up while holding the mechanism by the arms so that the rim is centered between the shoes. If the tightening nut isn’t loose, see if there are flats on the fixed seating pad, as shown in Figure 2-11. Slip a cone wrench (14-mm size, in most cases) onto those flats and twist the mechanism gently until the rim is centered between the shoes.

2-11 Side-pull Mechanism

(R) No handy flats on the seating pad? Try loosening the tightening acorn nut, then moving the mechanism by the arms to the right position, and tightening the nut again, making sure to hold the arms in the right position as you tighten the nut. If you have 2-pivot caliper brakes, you should be able to fix the one-shoe drag this way.

(R) Do you have single pivot calipers, and one brake shoe still insists on dragging along the rim? Take a good look at the shape of the fixed seating pad, which is against the frame tube on the mechanism side. (See Figure 2-11.) It might be curved so it fits the surface of the frame. If so, the brake arms are going to come back to the same incorrect position no matter how many times you loosen the tightening nut.

(R) If all the above attempts fail, you have to bend the spring to move the pushed-in shoe off the rim. First tighten up the tightening nut. Take your hammer, your big screwdriver, and your knowledge of these tools’ destructive tendencies, and approach the brake spring from above. (See Figure 2-11.) Set the tip of your big screwdriver on the topmost point in the curve or loop of the brake spring on the side where the shoe is off the rim. Got that? The opposite side from where the shoe is rubbing. Set the screwdriver as near as possible to vertical (the handlebars or the seat may make it a little awkward; the longer the screwdriver, the better) and give the screwdriver handle a tap with the hammer, lightly. No luck? Shoe still on the rim? Be firmer. But go easy. It’s all too easy to bend the spring too far, or put a big nick in it, or the frame tube, or your hand. Apply and release the brakes to check your shoe position when you think it’s right. If one shoe or the other always seems to be dragging, maybe the spring is old and weak. It’s time to overhaul the brake mechanism described below.

(M, R) Stickies. If the brake shoes are slow to grab the rim and slow to release it, and the handle and cable are both OK, then the mechanism must be rusty, mud-clogged, or broken inside. If there is some lubricant handy, squirt a drop on each pivot bolt. Then try grabbing a cantilever or brake arm with each hand and rocking them back and forth a bunch. Take the wheel off the bike and repeat the rocking action if you need to (just don’t push so hard on the cantilevers/brake arms that you break the springs or the mechanisms). Try loosening the pivot bolt, resetting the spring, and retightening the pivot bolt, as described in the One-shoe drag section, above. When you have the brake working passably, ride home and do an overhaul there, as described below.

(M, R) Brake mechanism overhaul: To overhaul your brake mechanism, all you really do is take each cantilever or brake arm off the mount (the pole thing that it pivots on), then clean and lube the parts, replace any that are ruined or rusty, and put the cantilever or arm back on the bike.

(M, R) Start by undoing the brake cable. Mountain bikers, take the removable end of the transverse cable out of its slot at the end of one cantilever or brake arm. It’s a good idea to leave the anchor bolt tight—you don’t need to move the cantilever very far to overhaul it. Roadies, undo the cable anchor bolt.

(M) When the cable is loose, use an Allen key to loosen the pivot bolt of one of the brake arms. It may be a bit difficult to turn even after the first twist or two; folks often use thread locking compound (like Loctite) on brake pivot bolts. When the bolt is all the way out, slide the cantilever arm off the mount, observing which hole in the mount plate the end of the spring is stuck into.

(R) When the cable is loose, loosen and remove the locknut and adjusting nut at the end of the pivot bolt, then remove the brake arms. Clean them and replace if necessary. See Figure 2-11 to identify all those little parts. Rebuild the mechanism the way it came apart, then adjust the adjusting nut so it works smoothly, hold the adjusting nut still with one wrench, and tighten the locknut with another.

(M) Turn the cantilever unit face down, so the end of the spring that was in the mount-plate hole is pointing up at you. Check the brass surface of the hole in the cantilever that pivots on the mount. This surface, called a bushing, should be perfectly clean, smooth, greased, and rust-free. If it isn’t, clean it with a cotton swab or corner of a rag, then smooth it with fine-grade emery paper or sandpaper wrapped around the mounting bolt or a Phillips screwdriver or some thing. Replace the cantilever if the bushing is too funky to save. Check the mount for a smooth, clean, rust-free condition, too. Being steel, it is more susceptible to rust. When both the mount and the cantilever bushing are smooth and clean, put grease on the mount.

(M) Next check the spring to see if either end is bent cock eyed; if the spring is bent, or if you have had lots of trouble with one-shoe drag and the bike is old, replace the spring AND its mate in the other cantilever, so you have a strong, well-matched pair.

(M) When all the parts are replaced or clean, smooth, and lubed, make sure the spring is pushed into the cantilever so the hidden end of it is in the socket down in there, then slide the cantilever back onto the mount, making sure the visible end of the spring goes into the same hole in the mount plate that it came out of. If your brakes are kind of slow to release, you can put the spring end in a higher hole in the mount plate, as long as you make a mental note to do the same thing with the spring in the other cantilever, so the two are balanced.

(M) When you have overhauled and remounted both cantilevers, push the brake shoes into the rim by hand and hook the removable end of the transverse cable back into its slot and ride in peace; you’ll be able to stop when you need to stop, and your brakes will release when you want to go.

(M ,R) What’s that? One-shoe drag problems? Oh dear. This sometimes happens after an overhaul, even if you did put the spring ends into the right holes in the mount plates; see the One-shoe drag section in this chapter.

(M ,R) Brake shoe cockeye: You banged your brake or it rattled loose, so one of the brake shoes hits the rim cross wise or not at all. Fix it quick, before it wears a hole in the tire or gets caught in the spokes. You have to loosen the nut on the mounting bolt that holds the shoe to the rest of the mechanism (if it isn’t already loose), then move the brake shoe around until you can see that it’s lined up so it’ll squeeze exactly on the middle of the wall of the wheel rim. It should look exactly like the one on the other side, so the two grab the rim at the same angle.

(M) Now, although the concept of lining up a brake shoe to mirror its mate sounds simple, in practice it can be as complex as family relationship dynamics. First you must make sure that the shoe is at the same level in its groove in the cantilever as its partner (they’ve must be coming from the same place, OK?). Then make sure the poles that hold the shoes are lined up at the same angle, and if possible, set the poles so equal amounts of them are sticking out from the cantilevers toward the rim, as shown in Figure 2-8. As if that isn’t enough, you must also make sure the brake shoe you’re aligning has a SLIGHT toe-in, so that when you look down on it from above, the end of the brake shoe that is toward the front of the bike is slightly closer to the wheel rim than the trailing edge of the brake shoe. Now, that’s a lot to get right all at once. If you’re at home, you can make the job a lot easier by taking the wheel off the bike, taking the tire and tube off the wheel, then replacing the tire-less wheel on the bike so you can align the brake shoes without having the tire blocking your view.

(M) When you finally get the brake shoe lined up, hold it there firmly with one hand while you tighten the mounting bolt. Take it easy on that bolt; they strip easily.

(M, R) Brake shoes worn or slipping. If your brakes don’t seem to work well and the shoes are worn down, don’t panic. Worn brake shoes can often work as well or better than new ones, if the brake system is adjusted and you use the brakes wisely. The first step to fix the brakes is to adjust them, as described in the Brake Cables section, above.

(M, R) If your brakes are slipping because they are wet, all you have to do is think ahead about your braking, and put the brakes on lightly for a few seconds to whisk the water off both the rim and the brake shoes, so the brakes will stop you when you need them. This technique will almost always keep the brakes from slipping and then grabbing in that terrifying way that wet brakes do.

(M, R) If your brakes are slipping from overuse and over heating on long, hot, steep descents, use them intermittently so they don’t get so hot and glazed. If the hill is so steep that you need to use the brakes almost all the time, alternate your use of the front and rear brakes. You may have to stop and let them cool, or cool the rims off in the water at a creek crossing. Whatever you do, avoid the nervous tendency to leave both brakes on lightly as you descend. That just burns them up.

(M, R) If your brake shoes really are worn all the way down to bare metal, here’s a last-ditch trick to get you home. See if there is a leftover ledge of brake shoe rubber that protrudes under if the edge of the rim when you put the brakes on. If there is a ledge like that, take a pocket knife and cut the thinnest outer edge of it off. CAREFUL: it’s easy to poke a hole in the tire as you do this. Then loosen the bolt that holds the shoe to the brake mechanism and shift the shoe alignment up so the new braking surface you have just made hits the middle of the rim wall. Tighten the mounting bolt while holding the brake shoe in its new position. Try out the brake to see if you have increased your stopping power. It won’t be up to snuff, but it’ll get you home if you take it easy. If the worn shoes wind up cock eyed, so they aren’t hitting the middle of the rim walls, see brake shoe cockeyed, above. Whatever you do, install new brake shoes before your next ride.

2-12 Brake Shoe

(M, R) Brake shoes squeaking or juddering. When you apply the brakes, your whole bike vibrates, and, if you’re going fast, your brakes screech like a Model T with its original equipment. Don’t let this bother you as long as the brakes stop you smoothly. If they are so juddery you can’t make controlled stops, first check to make sure the rims of your wheels are clean, and the cantilevers or brake arms are mounted tight to the frame.

(M, R) If your front brake is juddering badly, check the headset to make sure the bearings are adjusted right. Then check the brake shoe alignment. Get your head over the brakes and peer down past the tire at each shoe as you apply and release the brakes. Does the back end of either rubber brake shoe hit the rim before the front end? If it does, it will squeal or judder. On many cantilever brakes, you can loosen the mounting bolt and adjust the toe-in as well as the vertical and horizontal alignment of the brake shoe. You may have to twist a beveled (wedge-shaped) washer around the brake shoe mounting bolt, or shift the mounting bolt and some cupped washers to toe the shoe in properly. If you can’t get the brake shoes toed in right with gentle efforts, don’t fight them. Use the brakes sparingly to reduce your squeaking or judder problem on your way home. Then you may need to replace the shoes, the cantilevers (if they are cheapo ones that are loose and flabby on the mounts), or (if a front wheel is juddering badly) even the fork to solve your problem. Front wheel judder or fork flutter can be due to a combination of poorly aligned brake shoes, anodized or gritty/glazed rims, and a fork with too much fore-and-aft flexibility built into it.

Next: Coaster Brake

Prev: Brake Cables