- · Brake Systems
- · Brake Systems As Applied To 1970 BMW & Newer BMW Motorcycles ◊??
by Ron Schmidt Jeff Thurmond
Preface: The light turns yellow and you decide to stop, rather than run through the red as is the norm for Utah drivers. You apply the brakes; your BMW comes to a controlled stop. Brakes are just another part of our BMW that we expect to work flawlessly. But what is really happening when we apply the brakes?
In the simplest of terms, the brake system changes the moving (kinetic) energy of the bike and riders to heat energy. The heat is generated by friction between parts that rub together, and that heat is dissipated by the cooling air passing by it. The more heat a brake can generate and dissipate, the stronger the braking force is available. Once the brake is unable to dissipate the heat it has generated it will “fade” and become less effective.
The brakes on our motorcycles are capable of generating forces far greater than the engine develops. This can easily be understood if you think about how long it takes to accelerate your motorcycle to any speed and how much less time it takes to stop it from that same speed. So, next time some smart kid on a rice rocket says your BMW is slow, tell him that it makes over 200 HP. You don’t have to tell him that it is the brakes you are talking about!
Brake Basics: On a BMW motorcycles there are only two main types of brakes:
· Internally Expanding Drums
· Disc/Caliper
· There are varying styles and operating mechanisms for each. *
Internally Expanding Drum Brakes
Internally expanding drum brakes were used on the front and rear of all /5 models and /6 models 600cc and smaller. In later years, some of the airheads and K75 models still had drum brakes on the rear. All drum front brakes were double leading shoe (DLS); the rears were single leading shoe (SLS) types. All were mechanically operated by cable or rod. The necessary force needed to make these brakes powerful enough to be effective was supplied by the rider’s hand or foot applying force to a series of levers that multiplied that force. These levers include the hand lever or foot lever, the lever arms on the cam that operates the brake shoes, and the size of the cam itself.
Single Leading Shoe-- A SLS brake is the simplest of all BMW brakes. The two brake shoes are spread apart by a cam pushing on one end of each shoe, and pivot on a pin on the other ends of the shoes. The brake shoes are pushed out onto the inside of a brake drum. The rubbing of the shoes on the drum generate the heat.
Double Leading Shoe-- A DLS brake is just slightly more sophisticated but much more effective than a SLS brake. The part of the brake shoe that is closest to the operating cam in the direction that the drum turns is called the “leading edge” of the shoe. When the leading edge comes in contact with the drum, it has an amount
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