Here’s the brake maintenance tutorial for you.
Remove any locking devices from the pad-retaining pins; the pads can then be removed and the caliper piston eased back into its bore.
For the most part, all motorcycles built in the last 25 years, oddballs and some small dirt bikes excepted, use a front disc brake and either a drum or disc brake in the rear. While there are some variations on the basic disc-brake theme, the principles of inspection and pad replacement are common to most. Likewise, drum brakes, with some rare exceptions, are all serviced in the same manner. If there is anything truly unusual concerning your brakes, the shop manual should explain it.
Inspecting Disc Brakes
One of the advantages of a hydraulic disc brake system is that it’s self-adjusting. On the downside, this nicety often makes it hard to determine if the pads are worn without physically inspecting them. One indicator of pad wear is the fluid level in the master cylinder. As the pads wear, the caliper piston moves further out in its bore. Fluid from the master cylinder must then fill the space behind the piston. The first clue that the pads need an eyeballing may be a drop in the brake-fluid level. Typically, brake pads will have some sort of visual indicator to let you know how much life is left. These may be painted strips, slots cut into the pads or a step milled into the pad material. As the pad wears, so do the indicators; when they disappear, it’s time to replace the pad. Additionally, some manufacturers may specify a minimum thickness for the pad material; in most instances this is somewhere between 2.0 and 1.5mm.
These worn pads were discovered during a tire change; while the outside of the pad still had some life left, the inner pad is just about shot. Excess pad wear on one side indicates a sticky piston.
Normally the wear indicators are visible without removing the pads from the caliper, though you might need to remove an inspection cover to see them. By far, the worst method of inspecting the pads is the aural technique, which really amounts to not inspecting them at all. If you wait until you can hear the metal against metal grating of the pads grinding through the rotor, and assuming you get the bike stopped without hitting whatever it is you’re trying to avoid, consider the pads and rotors trashed beyond redemption.
If they’re a bit stubborn, reinstall the old pads and use a screwdriver to gently wedge them back.
Normally, neither the caliper nor the rotor cause many problems. Nonetheless, both should always be inspected along with the brakes. The rotor should be checked for cracks and wear grooves. Some grooving is normal, so don’t panic if yours has slight surface scoring. On the other hand, if the thing is worn like an old Elvis record, or has cracks radiating through it, replace it ASAP. The service manual will list the rotor wear limits, and most rotors will have the minimum acceptable thickness stamped into them somewhere. As a rule, motorcycle rotors don’t suffer the same type of erosive wear that car rotors do. Bike discs tend to be either obviously wiped out or OK. But it’s always a good idea to measure them just to be sure. Any that are below the minimum thickness should be replaced.
Most rotors will have the minimum thickness dimension stamped into them somewhere.
Disc brake calipers come in two flavors: the older-style floating caliper and the fixed caliper opposed-piston style. The floating caliper has the piston(s); there may be one or two located in one side of the caliper. As the piston applies pressure to the “live” pad the caliper is forced to move along a slide or pivot, which forces the “dead” pad into contact with the rotor, clamping it between the two pads. The second type, the opposed-piston caliper, has one or more pistons on either side of the caliper. Each piston exerts an equal clamping force on the rotor when the brake lever is applied. These calipers are rigidly mounted.
Caliper inspection points include the mounting bosses—look for cracks and stripped threads—the slide pins—check for corrosion and galling—and, if one is present, the dust boot on the caliper piston, which should be checked for cracks and tears. Caliper problems often make themselves known through accelerated brake-pad deterioration. If there seems to be an inordinate amount of drag on the wheel, or you begin to burn through pads more often then you should, chances are a caliper piston is sticking, or a floating caliper is seized on its slide.
Use brake grease to lubricate the pins before reinstalling it. Some antirattle springs may have directional arrows on them. This one almost went back together with the spring facing the wrong way.
Replacing the Worn Bits
Regardless of the type of caliper used, the pads are always retained in similar fashion. Most retention systems use some sort of hardened steel pin—the pin may be threaded on one end, or it may be held in place with cotter pins or spring clips. A third method is to secure the pin with some sort of retainer plate or plug.
Brake-pad replacement procedures vary slightly according to the caliper design. Your manual will provide the details. In essence the drill is to remove the brake pads from the caliper, retract the pistons, install the new pads, clean and lube up anything that slides or pivots and reinstall the whole shebang.
Take note of any datum marks between the lever arm and brake cam before separating them.
If you’re new to this, here’s the skinny. Remove the caliper from the bike—you don’t have to disconnect the hydraulic lines, just unbolt the caliper from its mount. (If the pads are removable with the caliper in place, and assuming you have enough room to work, you can skip that first step.) Remove the old pads. Most pistons won’t take much to force them back into their bores. A pair of moderately strong thumbs should do the trick: If your thumbs aren’t up to it or if you’re retracting multiple pistons, which may take a bit of fiddling to prevent back pressure from extending one or more of the opposing pistons, here’s a little trick: Place the old pads back into the caliper. Insert a pry bar or large screwdriver between the pads and wedge them apart—this will force all the pistons back into their bores at the same time. If that seems crude, feel free to use snap-ring pliers or anything else you fancy. The piston should retract smoothly. If it’s stubborn and evidence of a caliper problem exists—dragging brakes or premature pad wear, for instance—you may have a piston that’s sticking in the bore. If that’s the case, repairs should be made before the new pads are installed. Consult your favorite mechanic or the manual before proceeding. Don’t forget that retracting the pistons will displace some brake fluid. If you’ve been topping off the reservoir along the way, it may overflow; keep an eye on it in case some needs to be drained out.
Not much to them, is there? These new shoes come complete with new springs.
Once the pistons have been retracted, the new pads can be installed. In most instances I’d strongly suggest replacing all the brake hardware as well—that is, the slide pins, antirattle clips and any antisqueal plates. Under no circumstances should you reuse any locking devices or cotter pins.
Before reinstalling the calipers clean and lubricate any slides or pivot points using a high-temperature silicone brake grease. Torque any mounting hardware to the correct specification and use Loctite anywhere it’s required. Grease may find its way onto the rotor at some point, so give it a once-over with a clean rag and some brake cleaner, and don’t forget to pump up the brakes before riding the bike.
Many new brake-pad sets include the hardware.
Inspecting Drum Brakes
Drum brakes, at least as far as any current, mainstream motorcycles go, are only found on the rear wheel. Modern drum brakes are mechanically operated, so gauging the shoe wear is easy: When the cable or pull-rod adjustment is used up, so are the brakes. Most drum brakes also incorporate an external wear gauge as well, and occasionally some sort of inspection window. When the wear indicator reaches the end of its travel the shoes have had it, simple as that. Your service manual will also provide a minimum thickness dimension. Because drum brakes rely on stretch-prone springs to retract the shoes, replace ’em anytime new shoes are installed. Take a moment to examine the brake springs before you remove them. Occasionally, different-strength springs are used on the leading and trailing sides of the brake; interchanging them could cause the brakes to drag or fail to cleanly release.
Brake cleaner and a dedicated brake grease are all that should be used to clean and lubricate any brake-system components.
Drum Brake Service
Replacing the shoes will require wheel removal. The brake backing plate can then be removed and the shoes separated from the plate. Normally the shoes aren’t held in place by anything more than an “E” clip or a retaining washer, so no special tools are needed. Whenever the brake shoes are removed from the backing plate it pays to remove the brake cam and lubricate it as well. Before removing the brake arm from the pivot, take note of any datum marks. If none are present, use a punch to mark the arms’ location on the brake cam so you can replace the arm in the same spot upon reassembly.
Let’s see, the adjustment is about 2/3 gone; my guess is that a brake job is on the horizon.
Brake shoes, especially older ones, contain trace amounts of asbestos. So while you may be tempted to clean the drum by blowing it out with compressed air or brushing it out with a dry paintbrush, I’d advise against it. A better bet is to hose the thing down with brake cleaner, or even vacuum it out. The less of that stuff you inhale the better off you’ll be.
The brake drums may need some attention. Any light surface damage or glaze can be removed with 120-grit emery paper. It may be possible to remove deep scoring by turning the hub in a lathe, but you’re probably better off replacing it and checking the brakes more often in the future. If you’re inclined to turn the drum, your manual will list a maximum diameter service limit, and it should be stamped into the drum as well. While it’s unusual to see drums that have been worn oversize, it never hurts to measure them, even if it’s just for practice.
This BMW drum brake uses an “E” clip to hold the shoes in place.
Before reassembling the brakes, give the shoes and drum a wipe-down with a clean rag dipped in solvent or brake cleaner to remove any dirt and errant gobs of grease. Brake-adjustment procedures may vary slightly, but the idea is that when the brake is properly adjusted it shouldn’t drag, nor should there be excessive free play at the pedal. My method is to tighten the brake until I get a slight drag, then back the adjuster off until there is approximately one inch of free play at the pedal.
Before test riding the bike, give everything the once-over twice. Better to find out in the driveway that you forgot to tighten those caliper bolts than at the end of a 90-mph straightaway entering a 20-mph turn.
Remember that all brakes do require some break-in time before they’ll work at peak efficiency, 50 to 200 miles being about average. So take it easy for the first few miles and give them a chance to bed-in before pulling any stoppies.
This article was originally featured in the 2004 April issue of Motorcycle Cruiser.