MotoMojo - Brake Service and Maintenance

Text: Ken Freund • Photography: Ken Freund

Brakes are a crucial safety system, yet they seldom get attention unless there's a problem. Fortunately, minor brake work is within the capability of most experienced home mechanics. You don't need a lot of tools, and you can save a bundle of money doing it yourself.

If your brakes seem slow to stop, they pulse, or make unusual noises, if the brake lever feels spongy, or fluid is being lost, it's definitely time for service. These problems may be due to worn or glazed brake linings, warped rotors, sticking calipers or hardware. Brake fluid absorbs moisture; even if you haven't ridden your bike, fluid should be changed and the system bled every two years. First, obtain and read a repair manual for your specific motorcycle model. If you don't have the proper tools, experience, or skills, hire a qualified professional technician to perform the repairs. But if you feel confident doing it yourself, then start by suctioning out old fluid from the master cylinder reservoir. Refill with fresh brake fluid - whatever type is approved by the motorcycle manufacturer. Finally, bleed the system at the caliper bleeder fitting, until no more air comes out, and refill the reservoir; do this for both front and rear.

Squealing, which comes from brake linings vibrating in the calipers, can often be cured by sanding the pads and rotors with 120-grit emery cloth, and then applying anti-squeal compound to the back of the pads. This method is referred to as scuffing, and if the brakes are simply glazed, scuffing the pads and rotor surfaces may restore lost performance.
Pulsing is usually caused by warped or "wavy" rotors (discs) that have overheated from heavy braking or dragging brakes. If you haven't abused your brakes in this way, check for sticking caliper sliders and pistons. Some warped rotors can be resurfaced, but most likely they'll need to be replaced.

Spongy brakes or levers that sink are serious safety concerns. These and other hydraulic problems such as fluid loss, along with anti-lock brake system (ABS) concerns, should be repaired by a technician.
Low-pitched grinding that gets louder as you brake harder, usually results from worn-out brake linings. When disc brake pads wear, the caliper pistons move out, which lowers the brake fluid level in the master cylinder reservoir. If the level drops and no leakage is evident, check the brake pads for wear. On most bikes, you can shine a flashlight into the calipers to inspect the pads, which typically have painted lines and slots or steps, to gauge wear. Additionally, manufacturers specify minimum pad thickness, typically ranging between 1.5 and 2.0mm.

Check brake rotors for cracks, deep grooves, and scoring. Light grooves are normal, but if the rotor's surface looks rough or has cracks, replace it. If there's metal-to-metal grinding of the pad's metal backing rubbing against the rotor, it will probably require replacement. Measure rotor thickness, which requires a special brake micrometer - most shops have these and can measure for you. If any rotors are below the specified minimum, then replace. Most rotors have a minimum allowable thickness marked on them, and shop manuals include wear limits.

Replacing Brake Pads

Work in a well-ventilated area and avoid breathing dust. If the pads wear out quickly or are crooked, then a caliper piston is likely sticking, or possibly a floating caliper may have a sticking slider. Clean and lubricate any slides or pivot points, using sparingly, high-temperature silicone brake grease. It's also best to replace all brake hardware, including slide pins, clips, anti-rattle springs, and anti-squeal plates.

If your bike has floating calipers, you'll need to remove the caliper bolts and slip them aside to replace the pads. It shouldn't be necessary to disconnect the hydraulic lines when removing calipers. For most opposed-piston calipers, you can change the pads by simply removing the pins that hold them in place. These pins that position the brake pads are usually held in by small clips or cotter pins, or they're threaded on one end. Other types may secure the pin with a retainer plate or plug.
Gently pry the old pads apart to push the pistons fully back into their bores. (If pistons are stuck, the caliper may need to be rebuilt or replaced.) Pushing pistons in may overflow the master cylinder reservoir, so attach a small hose to route fluid into a catch can, before opening the bleeder screw. Close the bleeder screw as soon as the fluid stops flowing, and the piston will retract. Keep in mind that brake fluid harms paint, so be sure to wash it off with water immediately, if any gets on finished surfaces.

Remove old brake pads one caliper at a time, noting how the pads and mounting hardware fit. Clean parts with spray brake cleaner and a rag. Inspect calipers for cracks, leaks, stripped threads, damaged slide pins, and corrosion, and check the dust boots on the caliper pistons for tears.

Install new brake pads and hardware, and then reinstall the calipers (if removed). Apply blue Loctite on bolt threads, and tighten the fasteners to the factory-specified torque. Pump the brake lever/pedal repeatedly until the proper stroke and firm feel are restored.

Final Steps

Check everything you worked on, including fastener tightness, lever operation, and brake fluid levels. Wear full safety gear and test ride the bike in a safe area without traffic. You'll want to be able to stop without brakes, if necessary. Test the brakes, and of course, don't continue riding if anything doesn't feel right. If all feels good, then for the first 100 miles take it easy to allow the brakes to set in.