This is not the fluid worst I've run across, but it's ready to be changed. The rag prevents any spilled fluid from attacking the paint. |
Normally, brake-fluid specifications can be found in the owner's manual or imprinted on the master cylinder cap. |
Start by connecting a length of clear plastic hose to the caliper bleed screw. Run the other end of the hose into a clear plastic container. Pour a few ounces of fresh brake fluid into the container. This will seal the open end of the line and prevent air from siphoning back into the system. |
Open the bleed screw and pump the brake lever. You should see old, dirty fluid and perhaps a few air bubbles flowing out of the line. |
Pump the lever while keeping an eye on the master cylinder. Top off the master cylinder with fresh fluid whenever the level drops to the add mark. Don't forget to check your catch can occasionally. It's easy to overflow it with old fluid and create a real mess. |
Eventually you'll see only clean fluid flowing. At that point, tighten the bleed screw, pump the lever a few times and then, while holding the lever down, open the bleed screw as you normally would when bleeding the brakes. If no air bubbles or dirty fluid drains out, you're all done. If you're working on a dual-caliper brake, repeat the process on the opposite caliper. |
Top off the master cylinder, secure the cap and you're good to go for another year! |
Routine motorcycle brake maintenance is one of those dirty-dishes jobs: It's not very exciting, but the consequences of overlooking it certainly can be. If you've never experienced catastrophic brake failure, trust me, it's not nearly as much fun as it sounds. By inspecting your brakes and replacing them before they've given up the ghost, you can save yourself a world of hurt and a big chunk of cash.
Inspecting your brakes and, if need be, replacing the pads or shoes is a straightforward job well within the abilities of anyone who can read a shop manual. You don't even need much in the way of hardware. Besides the new brake pads, you'll only require a few common hand tools, a factory shop manual or its equivalent, some rags, a can or two of brake cleaner and a tube of high-temperature silicone brake grease.
For the most part, all motorcycles built in the last 25 years—oddballs and some small dirtbikes 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 similar. 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 farther 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. Some manufacturers may specify a minimum thickness for the pad material. In most instances this is somewhere between 2.0 and 1.5mm.
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 way to inspect 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.
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.
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, stripped threads and slide pins, and check for corrosion and galling. If one is present, inspect the dust boot on the caliper piston, and check 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 if you begin to burn through pads more often than you should, chances are a caliper piston is sticking or a floating caliper is seized on its slide.
Replacing the Worn Bits
Regardless of the type of caliper used, the pads are always retained in a similar fashion. Most retention systems use some sort of hardened steel pin. The pin may be threaded on one end, or held in place with cotter pins or spring clips. A third method secures 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.
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. It won't take much to force most pistons 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 there's evidence of a caliper problem, such as dragging brakes or premature pad wear, a piston may be 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, so keep an eye on it in case some needs to be drained out.
Once the pistons have been retracted, the new pads can be installed. In most instances I'd strongly suggest replacing all the brake hardware—the slide pins, anti-rattle clips and any anti-squeal 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 the brakes before riding the bike.
Drum Brake Service
Drum brakes, at least on current, mainstream motorcycles, 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 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. It's as 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 any time new shoes are installed. 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.
Replacing the shoes will require removing the wheel. The brake backing plate can then be removed, and the shoes can be separated from the plate. Normally the shoes aren't held in place by anything more than an "E" clip or a retaining washer, so you don't need any special tools. 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 arm's location on the brake camshaft so you can replace the arm in the same spot upon reassembly.
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 paint brush, I'd advise against it. A better bet is to hose the thing down with brake cleaner, or vacuum it out.
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, which 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.
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 grease gobs. 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. I 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.
For more articles on how to maintain and modify your motorcycle, see the Tech section of MotorcycleCruiser.com.