Brakes are so critical to a motorcyclist’s safety, yet many riders take them for granted until something goes wrong. Don't risk a crash. Brakes should be inspected regularly according to the factory maintenance schedule. If you notice that your brakes aren't stopping as well as they used to, make unusual noises, pulse, or the lever is soft and spongy (or brake fluid is being lost) it’s past time for service. These problems may be due to worn or glazed brake linings, warped discs (also called rotors), sticking calipers, or deteriorated rubber parts.
The good news is that most experienced DIYers can do minor brake work without a bunch of tools, and while saving a bunch of money. If you don't already have one, pick up a repair manual for your specific model motorcycle at your favorite shop or dealer, or on eBay or Amazon, etc.
Caution: Avoid breathing dust, work in a well-ventilated area and clean parts with spray brake cleaner and a rag, not an air blow gun. Brake fluid and sprays can get in your eyes, so wear eye protection. Flush with water if it gets in eyes. Brake fluid also harms paint, so wash it off with water immediately if any gets on finished surfaces.
Brake squeal usually comes from brake pads vibrating in their calipers. It can often be stopped by removing and sanding the pads and rotor(s) with 120-grit emery cloth, then applying some anti-squeal compound (available in auto parts stores) onto the backs of the pads. If brakes are simply glazed and polished (which often happens with city riding), but don't squeal, scuffing the pads and rotor surfaces as described may help restore diminished performance.
A low-pitched grinding sound and feeling that gets louder and more palpable when you brake harder is likely from worn out brake linings and should be fixed immediately. As brake pads wear, their caliper pistons extend, which causes the brake fluid level (in the master cylinder reservoir) to drop. If fluid levels drop but the lever is not spongy and no leaks are visible, check brake pads for wear. You may have to aim a flashlight into the calipers to check pad thickness, and in some cases remove them. Brake pads typically have painted lines or slots to help gauge wear. Manufacturers also specify minimum pad thickness, which typically ranges between 1.5 and 2.0mm above the metal backing at the thinnest point.
Brake pulse is generally due to warped or wavy discs that got overheated during heavy braking, or from dragging brakes. Some warped rotors can be resurfaced, but they usually need to be replaced. They are expensive, but can often be found on eBay for a reasonable price. If you have a pulsing brake, always check for sticking caliper sliders and pistons before replacing the disc.
Check your brake discs for deep grooves, scoring, and cracks. Very shallow grooves are normal, but if a disc surface is rough or cracked, replace it. Brake rotor thickness should be measured; rotors below minimum thickness should be replaced.
Special brake micrometers are required. Motorcycle and auto shops usually have them and can measure your rotors. If there was metal-to-metal grinding of the pad’s backing against the rotor, it likely needs replacement. Most rotors have their minimum allowable thickness stamped into them, and shop manuals also include wear limits. When in doubt, replace.
Brake Calipers and Pads
If your brake pads wear out quickly or wear unevenly, a caliper piston may be sticking. In the case of a floating caliper, there may be a slider sticking. Clean and lubricate any slides or pivot points, apply high-temperature silicone brake grease (available in auto parts stores) sparingly. It’s good practice to replace all brake hardware too, especially if bent or rusty.
Bikes with floating calipers may have to be unbolted to see or replace pads. However, you usually shouldn't have to disconnect brake lines when removing calipers. Simply remove caliper bolts and slip the caliper off. While it’s off, hang it from a piece of wire for support.
Removing the pins holding them in place can change brake pads in most opposed-piston calipers. These pins are usually held by small clips, cotter pins, or threaded on one end. Others may secure the pin with a retaining plate or plug.
Before removing old pads, gently pry them to push the piston(s) back in their bore(s). If pistons are stuck, the caliper may need to be rebuilt or replaced. Pushing pistons in may overflow the master cylinder reservoir. To prevent this, connect a small hose to the bleeder and route fluid into a catch can. Open the bleeder just as you begin to pry and close it as soon as the piston is retracted.
Remove brake pads one caliper at a time, noting how pads and hardware all fit. Take a photo to be sure. Inspect calipers for cracks, leaks, stripped threads, damaged slide pins, and corrosion. Check rubber boots on calipers for cracks or tears.
Install new brake pads and hardware and 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. Check fluid levels.
Spongy brakes or levers that sink are serious safety concerns. These and other hydraulic problems, such as fluid loss and anti-lock brake system (ABS) service, ought to be addressed by a technician.
Brake fluid is hygroscopic. Basically, it absorbs moisture from the air, which causes the boiling point to lower and the fluid to become corrosive. For prevention’s sake, you should change the fluid and bleed the brakes every two years.
There are several types of brake fluids in use. Silicone fluids are not compatible with conventional fluids, are generally used on restored vintage machines, and must not be used with ABS. You will see DOT type 3, 4, 5, 5.1, etc. Each has its own properties designed for specific applications, with different boiling points. Never mix fluids, or use old fluid from a container that has been opened. Always use the type recommended for your motorcycle. Your type is found on the fluid reservoirs, and in the owner's and shop manuals as well.
If you have ABS brakes, read the shop manual to determine if you can do the job yourself, or if it requires special equipment. For regular brakes, use a turkey baster to suck out the old fluid from the master cylinder reservoir. Refill with fresh brake fluid of the type approved by the motorcycle manufacturer, which is usually marked on the reservoir top. Bleed the system at the caliper bleeder fitting while pulling the lever until no more air comes out, then close the bleeder and tighten. Stop pumping and refill the reservoir before it goes empty. Follow a similar procedure front and rear. For dual discs, just do one at a time.
If you don’t have the proper tools, experience or skills – or feel unsure about any work – hire a qualified professional technician to perform the repairs. If you work on your bike yourself, double-check everything you work on, including fastener tightness, lever operation and fluid levels. Don full safety gear and test ride the bike slowly in a safe area with no traffic where you can stop without brakes if necessary. Test your brakes individually, and do not continue to ride if anything doesn’t feel right. If everything checks out, ride easy for the first 60-100 miles to let the new brake linings seat in.