MotoMojo: Motorcycle Brake Service

Apr 12, 2013 View Comments by

MotoMojo: Motorcycle Brake ServiceReplacing brake pads is something that most home mechanics can do with only a few common hand tools. A repair manual for the specific model should be available, and if you don’t have the proper equipment or skills, have a professional do the job.

Manufacturers give specifications for minimum pad thickness; typically this is somewhere between 1.5mm and 2.0mm. Many brake pads have painted lines, slots, or a step in the lining to gauge wear. They are usually visible without removing the pads, but you may have to take off an inspection cover. When these visual indicators are gone, or the pads become too thin, the pads should be replaced.

High-pitched squealing is annoying, but it’s often caused by brake pads vibrating harmlessly in their calipers. Often this can be cured by lightly hand sanding the pads and rotor and applying anti-squeal compound to the back of the pads.

Low-pitched grinding sounds that get louder when the brakes are applied harder are usually the result of metal-to-metal contact when the brake linings are worn away. In any case, brakes should be carefully inspected.

Pulsing as the brakes are applied is typically caused by warped rotors. This is usually caused by overheating, either from a sticking caliper or excessively heavy brake use. Check for sticking caliper pistons and sliding parts. Sometimes warped rotors can be resurfaced, but more likely they need to be replaced.

Now and then braking performance declines noticeably. This is usually caused by worn or glazed linings, sticking caliper pistons, or seized sliding hardware. Correcting these problems and scuffing brake rotor surfaces with 120-grit emery cloth to remove the glaze will often restore lost performance.

Spongy brakes or levers that sink (which are often the result of air in the hydraulic system or caused by a faulty master cylinder, hoses, or leaking calipers) are serious safety concerns. We recommend that repairs to antilock brake systems (ABS), and hydraulic problems such as fluid loss, be performed by qualified professional technicians.

As pads wear, the brake fluid level in the reservoir goes down. When brake pads are replaced, the fluid level should return to normal. Use

fresh brake fluid of the type specified by the motorcycle manufacturer, which is usually marked on the reservoir.

Inspect brake discs (rotors) for cracks, deep grooves, and scoring. Some light grooves are normal, but if the rotor’s surface looks rough or has cracks, replace it. You should measure rotor thickness and scrap any that are below minimum. If there was metal-to-metal grinding of the pad’s backing against a rotor, it will probably need replacement.

Brake rotors have a minimum allowable thickness marked on them, but if you can’t find that, shop manuals include wear limits. Special brake micrometers are used; most motorcycle shops have them and can measure your rotors.

Pad replacement procedures vary by caliper design. Typically, at least part of the floating calipers must be unbolted to replace pads that fit inside the caliper, while the pads in most fixed calipers can be replaced by removing pins. It shouldn’t be necessary to disconnect hydraulic lines—just remove the caliper bolts.

Brake pads that are retained with metal pins are often threaded on one end or held in by small clips or cotter pins. Others may secure the pin with a retainer plate or plug. Check the repair manual and/or instructions that come with the pads.

Before you remove the old pads, put a screwdriver tip between the pads and push them apart slowly to force the piston(s) all the way back into their bores. Retracting caliper pistons displaces brake fluid and may overflow the master cylinder’s reservoir. We recommend opening the bleeder screw and attaching a small hose to direct the fluid into a catch container. Brake fluid ruins paint; wash it off with water immediately.

Remove old brake pads one caliper at a time, noting how they are held in place and how mounting hardware fits. If you have twin calipers, you can use the other one as an example of how everything fits back together. Clean parts with brake cleaner and a rag to avoid blowing dust.

Check calipers for cracks, leaks, stripped threads, damaged slide pins, and corrosion. Inspect dust boots on the caliper piston(s) for splits and tears. Sticking parts can result in rapid or crooked brake wear. If a wheel is difficult to turn by hand, or pads wear quickly, a caliper piston may be stuck, or a floating caliper may be seized on its slide. If pistons are stuck in their bores, the caliper should be replaced or rebuilt.

Clean and lube slides (or pivot points) sparingly using high-temperature silicone brake grease (sold at motorcycle shops and auto parts stores). It’s recommended to replace all brake hardware, including slide pins, anti-rattle springs, and anti-squeal plates.

Install brake pads and hardware, and reinstall calipers if they were removed. Use blue Loctite on threads, and tighten fasteners to the torque specified in the shop manual.

Pump the brake lever until the pads seat against the rotor and normal brake ‚”feel” is restored. Check over everything you worked on, including fastener tightness, lever operation, and brake fluid level, and do not ride if anything isn’t right. Test brakes in a safe area away from traffic, with helmet and full safety gear. Then take it easy.

Text and Photography by Ken Freund

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