The start of a new season: your bike has been stored away for the winter and now it’s time to ride … not so fast, though. You’ll need to check a few things first, and maybe some light maintenance is in order. Sure, you’ve changed the oil, charged the battery, and checked your tires. What else? Brakes, that’s what. You’ll want to stop, won’t you?
Now is a great time to examine your brakes for proper operation, for disc pad wear, and to change your brake fluid. The fluid should be changed every two years anyway, and I’ll bet it’s been more than two years since the last time. Brake fluid (DOT 3 and DOT 4, used in almost all bikes) is hygroscopic: it absorbs moisture from the air. The moisture causes corrosion in brake lines, calipers, pistons, and it can also rot seals. So, it’s important to change the fluid regularly. And it’s not as hard as you might think.
However, if you’re not confident about wrenching on your bike, don’t mess with the brakes. Obviously, these are critical safety components, and you need them to work reliably. If in doubt, take your bike to a qualified service technician. The following procedures describe changing the fluid in your front brake, but the same principles apply to the rear.
Assemble the items you’ll need: a brake bleeding kit (sold at most automotive outlets, although a length of clear plastic tubing of the right diameter and a catch bottle will work too); fresh brake fluid in a new, sealed container; lint-free rags (not paper towel); torque wrench and sockets; and a wrench that fits the brake bleed nipple.
Cover the bike’s bodywork around the master cylinder and fluid reservoir (at the brake lever) with cloth or paper towels. Brake fluid will strip paint, so you don’t want to get it on the bodywork (if that happens, wash it off straight away with water and detergent). Clean the outside of the fluid reservoir and remove the cap. Hook up the bleed kit to the bleed nipple on the brake caliper and release the nipple with the wrench—a quarter turn is usually all that’s required.
The most efficient way to drain the fluid is to follow this sequence: open the nipple; squeeze the brake lever; close the nipple; and release the brake lever. Fluid should flow out of the nipple when you squeeze the lever, but should not suck back into the caliper when you release the lever. Be sure to squeeze the lever slowly, or else back pressure may spray fluid out of the reservoir. Try this routine a couple of times and you’ll get the idea. Some brake bleeding kits have an automatic non-return valve, which makes bleeding a lot easier: follow the instructions.
When you’ve drained all the fluid from the reservoir, clean the inside with a lint-free cloth to remove the fine sediment that always seems to accumulate there.
Next, remove the bleed kit and check your brake pads. You can often see how much pad material is left without removing the caliper from the fork, but if it’s not obvious, remove the caliper. They’re usually held on with two bolts. If you have less than, say 1/8-inch of pad material left, it’s probably time to change them. Remove the caliper from the fork if you haven’t already done so.
Check the disc rotor for wear. If the surface is grooved at all, gauge the thickness with a micrometer and refer to your owners’ manual for rotor thickness limits. The rotors can often be turned down to remove grooves, but only if there is sufficient thickness. If in any doubt at all, take your bike (or the wheel) to a qualified technician.
With the caliper off the fork, remove the disc pads. These are usually held in place with a retaining clip and bolt (Nissin) or a couple of pins (Brembo), but if unsure, check your owners’ manual. Next, lever the pistons back into the calipers a little way with a tire iron or flat blade screwdriver to make room for the new pads. (Don’t do this with the calipers mounted by levering against the disc rotor! Always remove the calipers before replacing disc pads.)
Keep an eye on the fluid reservoir while replacing pads because some fluid may be forced back up the brake lines. If this happens, clean out the reservoir again with more lint-free cloth. If the pistons won’t move smoothly, or if there is any sign of fluid leaking, the calipers will need rebuilding or replacing. Take them to a specialist.
Install the new disc pads and refit the caliper on the fork. Use a torque wrench to tighten the bolts to the correct torque—refer to your bike’s shop manual. Top up the reservoir with clean, fresh fluid from a sealed container. NEVER reuse brake fluid. The reservoir cap will indicate whether you need DOT3 or DOT4.
The next step is probably the most critical, because it’s vital to remove air from the brake lines. Repeat the bleeding process described above (open nipple, squeeze lever, close nipple, release lever) until the fluid flowing out is clean, clear and free of air bubbles. Make sure you keep the reservoir topped up, or you’ll suck more air into the system, which means you’ll have to start over. If you have dual discs on your bike, you’ll need to repeat the process for both calipers.
After tightening the bleed nipples, check the brakes for operation. The lever should not feel “spongy” when you operate it. If it does, or if the lever moves too far, you may still have air in the system. Repeat the bleeding process. Occasionally, the last few air bubbles will be trapped in the system, and you may need to take you bike to a technician. They have access to expensive vacuum brake bleeding machines. Usually, though, that assistance isn’t necessary.
Road test your bike in a safe area, preferably off the highway, to make sure the brakes are working properly. New pads may take a few applications of braking to “bed in,” and you may find the first few times you use your brakes that they don’t grip as well as they used to. Brake response should improve quickly, however. But if it doesn’t, it’s back to that qualified technician!
Brakes are the most important safety devices on your bike, so it’s vital they work properly. Making sure your brake system lasts by changing fluid regularly (every two years) is cheap insurance, which is going to save you money over the long haul too!
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