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The standard for mountain bike brakes is: your brakes should be able to stop your bike
within 15 feet while a 150-pound rider is going 15 mph. (And they shouldn't screech or
wobble.)
Optimum brake performance also depends on undamaged rims and a true tire
alignment (perfectly round rim with no lateral warpage) -- you may need to replace or true
your rims to get your brakes working right. This section describes a basic tuneup and
cleaning. Please see other sections for brake pad replacement
or truing of rims.
If your brake cables have dirt in the housing, the brakes may be hard to
pull, or the calipers may not rebound away from the tire when you let off the
brakes. See the section on cable cleaning.
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Clean all visible brake parts with a brush. Soapy water works fine. If
there's substantial oil or grease buildup, use a degreasing solution. Release the brake
cable by detaching the retaining clip from the cable housing.
Detaching the brake cable from a V-brake system. |
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Coil-spring brakes may be more susceptible to gumming than those with an
external spring. To remove the caliper for cleaning, first release the spring tension by
backing out the tensioning screws on each side. Loosen the
tensioning screw to relax the spring before removing the calipers. |
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Now unscrew the mounting bolt to remove the caliper. Clean the spring and
bushing thoroughly. Relube and remount the calipers. Don't get grease on the rim or tire! Removing the caliper to clean the swivel and spring. |
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Check the brake pad for wear. A ridge of unworn pad on top or bottom means
your brake isn't hitting the rim squarely. Replace worn-down or
unevenly worn pads. Inspecting the brake pad. |
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Check the rim for damage. If you do much mud-riding, the rim may wear
thin. As the brakes push in, the metal curves inward. Cracked or buckled rims need
replacement. If there are local rock-bites on the rim, smooth the ridges off with
ultra-fine sandpaper. If the rim is widely rough, clean and smooth the rim with steel
wool.
Inspecting the rim. |
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Now reattach the brake cable to begin aligning the brake pads. Reattaching the brake cable. |
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Go to the brake lever. Turn the adjusting knob back, leaving only about
1/8" of space between the knob and the lever housing. Backing
off the cable length adjuster. |
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Loosen the cable retaining screw on the caliper. Take up extra cable until
each brake pad is about 1/8" from the rim, then tighten the retaining screw.
Loosen the stem of the brake pad. On V-brakes, this is done with
the
nut at the end of the stem.
Adjusting the cable length. |
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Slide the stem of the brake pad up or down within the slot
in the caliper, until it's exactly perpendicular to the plane of the rim as the pad
touches. Turn the pad so it's aligned along the center of the rim along its entire length.
Tighten very slightly.
Toe the brake in slightly at the front end.
This means the FRONT end of the brake pad will be a trace closer to the rim than the back
end. (Screeching brakes are fixed by toeing the brake pad.) Put a couple of
business cards under the back end of the pad, then grip the brake lever to
tighten the pad down against the rim. Now tighten the stem fully.
Positioning the stem (push-arm) and brake pad. |
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Using
the tensioning screw, add rebound to the calipers until they spring away from the rim
strongly. Rotate the tire, while watching the position of the pads in relation to the rim.
If the rim is not true, both brake pads may hit the rim at different times as the tire
rotates. If so, you need to true the rim before proceeding.
Checking clearance. Checking stem and brake pad alignment. |
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Grasp the brake lever and stop the rotating tire several times. Check the
position of the pads relative to the rim. If one is closer (or rubbing), tighten its
tensioning screw (turn the screw IN) so the caliper rebounds further away from the rim.
Repeat adjustments of 1/4 turn until the pads remain equally spaced. Adjusting
the spring tension. |
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Tighten the brake cable with the adjusting nut at the brake lever. Goals:
(1) The pads shouldn't hit the rim. (2) As you pull the lever, the brakes should engage at
a point that's comfortable for your hand. (3) You should have around 1-1/2 inches of
daylight between the lever and the handlebar when you're pulling hard on the brake. Some
riders like a closer grip, leaving only about 1/2," but this puts you at risk of
"bottoming out" the lever with the brake only partly engaged. Fine
adjustment of cable length. |
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If you ride in mud, you may need extra room between the pads and the rim.
Loosen the cable slightly. Be sure you still have plenty of space left between the lever
and handlebar, so you'll retain braking power as the pads wear down. Checking
brake lever position. |
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If your fingers are short, or you like the levers a bit closer to your
hand, you can adjust the lever's starting position. The adjustment screw opposite the
lever can be used to swing the lever back towards the handlebar. (This gives you less
total brake-lever motion, so the tuning of the brakes needs to be more exact.) Adjustment of brake lever starting position. |
If you hear a grinding or feel a rubbing sensation when you apply the brakes
(while the bike is standing still), your cables are full of crud. You should
perform a complete cable cleanout. If the cable or the
housing is bent or damaged, you should replace the
cable.
Ride the bike around for 1/4 mile or so, pulling hard on the brakes. Now recheck the
pad alignment and lever position.
[Fix-it Index Page]
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