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Brakes
About Brakes
The technology behind brakes has changed dramatically over the years. On very early cars the brakes were
sometimes a literal pad applied to the tire on the end of a pressure rod (like was done with wagons). These
days we have computer controlled self-activating disk brake systems in some cars that will actually activate
whether you hit the brake pedal or not!
Within the scope of most restorations there are two distinct types of brakes, and depending on the age of
your car you may have one or both of these types. The first is a drum brake, which is an early style of brake,
but is still commonly found on the rear wheels of modern cars. The second is the disk brake, which is more modern
and effective in terms of stopping power. The primary difference between the two is that a drum brake uses internal
pads to press outward against a steel drum that spins with the tire wheras the disk brake uses a caliper that
squeezes against a rotor which spins with the wheel.
Brake Components
A vehicle braking system is comprised of the following elements at a minimum:
- Brake pedal
- Well, d'uh, otherwise there's no way to use the brakes. :)
- Brake Master Cylinder
- This could be a single or a dual master cylinder, it may also be interconnected with the clutch cylinder.
This is the initial source of braking power.
- Brake Lines
- These connect the master cylinder to the wheel cylinders / calipers depending on brake type.
- Wheel Cylinder (Drum Brakes)
- This cylinder applies pressure to the brake shoes when the brakes are engaged.
- Caliper (Disk Brakes)
- The caliper contains one or more cylinders that cause the caliper to compress when the brakes are engaged.
- Brake Shoe
- This part is applied against the brake drum to create braking force.
- Brake Pad
- The brake pad sits between the caliper and the rotor and is the source of friction for brake.
- Brake Drum
- The drum is the point where the force is applied to slow the motion of the wheel.
- Rotor
- The rotor is the point where the force is applied to slow the motion of the wheel.
- Parking Brake
- A cable based assembly that causes the rear brakes to lock when engaged.
The extended system
- Brake Booster
- This is a vaccum based assembly that provides power assistance in engaging the brakes.
- ABS
- ABS is an electrical system that causes the brake calipers to fluctuate under braking akin to pumping
the brakes. This is a modern technology (though initially developed in the 20's).
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How it works
For all the bits and pieces involved brakes are really a simple system. The brake system is hydraulically based.
When you push down on the brake pedal it forces a plunger in the master cylinder to be compressed. If equipped with a
brake booster, the pedal first interacts with the booster and the booster applies the pressure to the master cylinder.
This compression
puts hydraulic force on the brake fluid. The fluid is then forced from the master cylinder through the brake lines to
the brakes. In the event that the brake is a disk brake, then the fluidic pressure expands a piston in the caliper that
causes the caliper to pinch against the rotor. At this point the brake pads, our friction source, are pressed against
the rotor slowing the motion of the wheel. In the case of drum brakes the wheel cylinder expands which puts pressure on the
brake shoes. The brake shoes are then pushed out to contact with the brake drums. The friction surface of the brake shoe
causes the drum to spin more slowly, thus slowing the vehicle.
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