Bicycle Repair Adjusting brakes


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How to adjust common bicycle brake systems

The brakes on bicycles are simple to adjust. They are an essential piece of safety equipment, so learning to adjust them is a worthwhile skill. Remember: after adjusting brakes, always try them in a safe environment before riding.

Rim brakes

Most bicycle brakes use a lever on the handlebars to pull a cable: that cable draws together a pair of brake arms, pressing the brake blocks (aka pads or shoes) against the rim of the wheel. Friction between the blocks and the rim is what slows the bike down.

First, check that you have good brake blocks and rims. Rims should be free of corrosion and dirt, and the brake blocks should be appropriate for the rim. Replace worn blocks in pairs.

The blocks should be aligned with the rim and slightly toed-in (to prevent squeal). To adjust them:

When both blocks are aligned correctly, slacken the brake cable clamp bolt and, using pliers, pull the cable through and hold it tight. Hold the brake blocks close to the rim and tighten the cable clamp bolt. This may take a couple of tries to get the blocks close to, but not touching, the rim.

A fine adjustment may be made with a screw-thread adjuster barrel where fitted. This may be located where the brake cable goes into the brake lever by the handlebars, or for side-pull brakes, near the brake blocks. A knurled locknut keeps the adjustment locked in place. If the brakes just need a small adjustment, the fine adjustment may be all you need to do. Before making the cable clamp adjustment per the previous paragraph, first adjust the fine adjustment to the maximum block-to-rim clearance. This will permit a future full-range fine adjustment.

Note: A regular, periodic rubbing when the wheel is spun indicates that the wheel is out of true and needs to be trued.

The brake should be centered so that both blocks apply equal pressure to the rim. The method varies:

Changing a brake cable

Brake cables are braided wires with a metal lump at one end. This lump is a specific shape and is called the nipple. Usually, drop-handlebar ("racing") brake levers have a pear nipple and straight handlebar levers have a barrel nipple. Universal cables are available which have one at each end; one cuts off the end one doesn't need.

Brake cables run through a protective shroud called an outer or cable housing for part or all of their length. The section leading from the handlebar to the frame is always surrounded by an outer, which together with the inner wire cable forms a bowden cable and allows force to be transmitted from the levers to the mechanism on the frame through a flexible connection. On bicycles with suspension a similar arrangement transmits the force from the frame to the fork, and on these and many touring bicycles the one cable outer may lead all the way from handlebars to the forks.

On other bicycles, especially racing bicycles, the cable is open where it runs along the frame. Small pulleys are used where the open cable must change direction, unlike the covered cable which may simply turn a corner. Use of open cables reduces both friction and weight. A single continuous inner cable normally runs from the nipple end at the handlebars through several cable sheaths to the caliper mechanism.

To remove an old cable, slacken the cable clamp bolt on the brake. Pull the cable through the outer until it is all out at the lever, then remove the nipple from the lever and discard the cable. Steel cables can be recycled.

To install the new cable, put a little grease on the nipple and locate it in the lever. Then feed the other end of the cable through the cable outer, adding a little grease, until it emerges near the brake. Feed the end through the clamp bolt and adjust the brake as described above.

A new brake cable will stretch in use. You will need to take up slack after the first hundred miles or so, by adjusting the cable in the usual way.

Disc, drum and coaster brake systems




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