Motorcycle Brakes - Part 2
Three basic brake configurations are found on motorcycles. These are single leading shoe, double leading shoe, and disc brakes. Each has its own special use and strong points.
Single Leading Shoe
The single leading shoe brake has a single brake cam and two brake shoes with stationary pivot points.
The front or Leading shoe is "wedged" into the drum as the brakes are applied because the rotation of the drum tends to pivot the shoe on its pivot point and turn it into the drum. This action results in a "self-energized" brake because the more the brakes are applied, the harder the brake shoe is forced into the drum.
The trailing shoe, on the other hand, is pivoted away from the rotating drum. The advantage of a trailing shoe is that it becomes a leading shoe when the motorcycle is rolling backward, or when it is stopped on an uphill grade. Some Trail and Enduro bikes use single leading-shoe brakes front and rear because of this characteristic. Most street machines use single leading-shoe set-ups on the rear to ease the bikes' roll-back tendency when stopped at a light on a steep uphill grade. In addition, they are simpler, lighter, and cheaper than other types of brakes.
Double Leading Shoe
Bigger, faster machines demanded advances in brake designs to keep pace with powerful new engines and better handling frames and suspensions. The full-width, double leading shoe front brake emerged as the answer to stopping problems for most of these machines in the Sixties and Seventies. Since the front brake is responsible for about 75 per cent of the stop, it needs a more efficient system to handle all the weight that shifts forward during braking.
All that's needed to re-engineer a single leading shoe brake into a double leading shoe system is the addition of another cam and some linkage to actuate and adjust it.
Each shoe has its own engagement cam and pivot points. These cams and pivot points are opposite each other so that each shoe can be "self-energized" by the rotating drum. Naturally, it is critical that each shoe be adjusted to engage the drum at the same time and at the same rate. Poor double leading- shoe brake balance adjustment can result in jerky, dangerous stops and erratic braking action.
In both the single leading-shoe and double leading-shoe arrangements, the backing plate must have a firm anchor to lock it to the frame. There is always a torque stay strap or a locking lug to prevent backing plate movement during braking.
Disc brake systems are fortunately the current standard and they employ a round, solid steel plate or disc attached to the rotating wheel. Two fiber brake pads or "pucks" are located in a caliper assembly that is attached firmly to the fork or swing arm. When the brakes are applied these pads are squeezed together against both sides of the disc, creating the friction and heat needed to stop the bike. The disc brake is superior to the drum brake because it is fade resistant, smoother operating, self-cleaning, and easier to service.
Most disc brakes employ a "floating caliper" where the caliper can slide on its bracket. This enables the caliper to move sideways during engagement to insure firm contact by both brake pads even though only one pad is activated. There are many variations on this theme to be found on modern motorcycles, but the essential functions stay the same throughout.