Calliper brakes are found on road bikes. For best performance, these brakes must be adjusted so that your wheel will run cleanly between the blocks without touching either block.
However, the blocks must be close enough so that when you pull the lever the blocks bring the wheel to a stop when the brake lever is somewhere near the middle of its travel. You shouldn’t be able to pull the brake-lever back far enough to touch the handlebars. This means you haven’t got enough power to bring the bike safely to a stop. Some prefer a little bit of movement of the levers before the brake blocks bite as it means they can get a proper grip on the lever.
This adjustment will only work if the wheels are aligned centrally in the frame. Check that the gap between the tyre and the frame or fork is the same on either side of the wheel and realign the wheel if necessary.
Step 1 : Before you adjust anything, make sure the brake cable isn’t seized or sticky. Undo the cable pinch bolt so that it’s not gripping the cable at all. Pull down gently on the cable and squeeze the brake-lever at the same time. You should feel the cable pulling upwards. When you release the brake-lever, a gentle tug should pull the cable smoothly back through again. If the cable feels rough or gritty, then change it.
Step 2 : Check where the cable lies as it clamps under the pinch bolt. There will always be a groove marking the correct place and there will always be a washer – often a specially shaped one – between the cable and the pinch bolt. Squeeze the brake blocks onto the rim with one hand while pulling through any slack cable with the other. Let go the cable, but keep hold of the block and tighten the pinch bolt firmly.
Step 3 : Squeeze the brake-lever firmly several times to settle slack out of the cable. You may now find that you can pull the brake-lever all the way to the bars. If so, you need to pull through slack cable at the calliper again. Hold the cable just where it emerges from under the cable clamp bolt, undo the cable clamp bolt a couple of turns, pull through any slack cable and retighten the cable clamp bolt firmly.
Step 4 : Check the gap between the brake blocks and rim. Spin the wheel gently. The blocks shouldn’t touch the rim. Squeeze the brakelever you should be able to get about halfway to the bars. Make minor adjustments with the barrel-adjuster. Turning the barrel-adjuster out of the calliper will bring the blocks closer to the rim, turning it into the calliper moves the blocks further away. Experiment to find the best position.
Step 5 : You may find that the brake block on one side touches the rim, while the other block doesn’t. Newer callipers have a balance screw that allows you to readjust the angle of the whole calliper. Try to remember which way the balance screw turns; just experiment as different mechanisms have opposite effects. Turn the screw gently – quarter of a turn at a time – until the rim runs centrally between the blocks.
Step 6 : You may find the blocks are way off to one side, further than the balance screw can correct, or you may have a calliper without a balance screw. If so, you’ll have to adjust the position of the whole calliper. Hold it as shown and undo the calliper fixing bolt until the calliper swings freely. Correct its position and retighten the calliper bolt firmly. If you’ve got a balance screw, use it now to make final adjustments.
Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES