and the valve has no effect on braking. Since the clutch
pedal is in the raised position at this time, the mechanical
connection also keeps the ball from seating. When the
driver stops on an uphill grade and depresses both the
clutch and brake pedals, the ball rolls into contact with its
seat. Since the clutch pedal is depressed, the mechanical
connection is moved away from the ball, allowing it to
seat. This closes the valve, trapping hydraulic pressure in
the right rear and left front wheel brakes. The driver can
release the brake pedal with no risk of the vehicle rolling
As long as the clutch pedal is depressed, the ball
remains seated. Without the need to depress the brake
pedal, the driver can engage the clutch while pressing the
accelerator pedal for a smooth takeoff. As the clutch is
engaged, the mechanical linkage moves the ball away
from its seat, releasing the hydraulic pressure in the wheel
Brake Light Switch
To operate the brake lights, a brake light switch or
stoplight switch is installed on the brake pedal linkage.
One end of the brake pedal switch is mounted to the vehi-
cle body under the dashboard. The other end is installed
on the brake pedal linkage. The two most common types
of brake switches are the plunger type, Figure 9-18, or the
pin actuated type.
Some vehicles use a sliding contact brake light
switch, Figure 9-19. This switch can be easily recognized
since it is much larger than other types of brake switches.
The sliding contact brake light switch also contains the
brake switches for the cruise control and anti-lock brake
systems when they are used.
With either type, switch operation is the same;
pressing on the brake pedal causes the end of the switch
assembly to move in relation to the end mounted on the
body. This movement causes the switch contacts to close,
completing the electrical circuit between the vehicle bat-
tery and the brake lights. Completing the circuit causes the
lights to illuminate.
On some vehicles, the brake switch has battery cur-
rent at all times, and the brake lights will come on when-
ever the pedal is depressed. On very old vehicles, the
brake switch power is routed through the ignition switch
and the brake lights can illuminate only when the ignition
switch is in the on position.
Brake Lines and Hoses
For the hydraulic pressure developed in the master
cylinder to reach the wheel brakes, they must be connect-
ed by some sort of hydraulic tubing. This tubing consists of
rigid steel lines and flexible rubber hoses.
Steel Brake Lines
Whenever possible, the hydraulic system uses rigid
steel brake lines, sometimes called tubing, to transmit
hydraulic pressure. Steel lines are resistant to collision dam-
age and vibration, can stand up to high brake system pres-
sures, and are relatively inexpensive. For added safety, the
steel used in the lines is double-wall (double thickness)
welded steel made from copper-coated sheet steel.
Common steel line sizes range from 1/8-3/8” (3.25-9.5 mm).
Steel lines are often coated with tin, zinc, lead, or
Teflon™ to reduce damage from corrosion. The lines are
clamped to the vehicle unibody or frame at close intervals
to reduce damage from vibration and road debris. The
clamps often contain rubber bushings to reduce the
possibility of normal vehicle vibration rubbing a hole in
the line. Figure 9-20 shows typical steel line construction.
158 Auto Brakes
Figure 9-18. A plunger type stoplight switch assembly. 1–Brake
pedal mounting bracket. 2–Switch retainer. 3–Stoplight switch.
4–Stoplight switch mounting bracket. 5–Switch actuator lever.
6–Brake pedal. 7–Plunger. 8–Normal brake pedal travel.
(General Motors)
Figure 9-19. A slide brake light switch is used with some anti-
lock brake systems. 1-Cruise control terminal. 2-Switch assem-
bly. 3-Washer. 4-Retainer clip. (General Motors)
2 2
4 4
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