BRAKE SHOE ASSEMBLY
Vehicles are
equipped with leading/trailing brakes, identified by adjuster screw
hole in backing plate, located above horizontal centerline of rear
axle. All other models are equipped with dual-servo brakes,
identified by adjuster screw hole at bottom of backing plate. Brake
assembly consists of backing plate, brake shoes, return springs,
automatic adjusting assembly and a wheel cylinder. Automatic
adjusting assembly consists of an actuator lever, return spring,
actuator link, adjusting screw and spring. Automatic adjustment is
accomplished through movement of actuating lever and
secondary shoe.
BRAKE WARNING LIGHT
Pressure
differential warning switch in combination valve energizes brake-
warning light on instrument panel when front or rear brakes lose
hydraulic pressure. After repairing failed side of hydraulic system,
depress brake pedal with moderate to heavy pressure to
hydraulically center the piston. This will turn off brake warning light.
On vehicles with Hydro-Boost, insufficient flow of power steering
fluid to the hydraulic booster system will turn on brake warning light.
FRONT CALIPERS
Front brakes
are floating caliper or sliding caliper design. Rear brakes are
sliding caliper design. Caliper is attached to caliper mount. Caliper
is mounted to steering knuckle or caliper adapter, depending on
application. Caliper assembly slides back and forth in machined
cutouts.
REAR CALIPER
The rear disc brakes use a Bendix caliper. The caliper
mounts to the anchor plate in a way that allows the caliper to move
laterally against the rotor. The calipers a one piece casting with
the inboard side containing a piston bore. A square-cut rubber
seal fits in a groove in the piston bore to provide a hydraulic seal
between the piston and caliper bore.
HYDRAULIC CONTROL
VALVES
Combination Valve
System uses a combination
valve to regulate brake system hydraulic pressure. Combination
valve, located in brake lines between master cylinder and wheels,
has 3 pressure control functions: l Metering (or hold-off) section of
valve limits pressure to front brakes until pressure of rear brake
shoe retractor springs is overcome, then allows pressure to front
brakes. l Warning switch section of valve constantly compares
front and rear brake pressures from master cylinder.
Proportioning section of
valve allows input pressure to rise to predetermined level before
allowing output pressure to rear brakes. This prevents rear wheel
lock-up on vehicles with light rear wheel loads. Combination valve
also contains a by-pass feature. This ensures full system pressure
is applied to rear brakes if front brakes lose hydraulic pressure (or
if rear brakes lose hydraulic pressure, full pressure is applied to
front brakes.
Height-Sensing Proportioning Valve
Valve
senses vehicle load conditions through relative movement
between rear axle and body. As vehicle load increases (resulting
in decreased vehicle height), valve allows higher pressure to rear
brakes, resulting in optimum front-to-rear brake pressure balance.
REAR ROTOR
The rear
disc brakes use a combination rotor and hub assembly. The rotor
is integral with the rear hub. During operation, the rotor turns
between the linings and basically free wheels until the linings
begin to apply a clamping action on it. The vented area between
the rotor braking surfaces allows for efficient heat dissipation.
WARNING
On vehicles with height
sensing proportioning valve, use of aftermarket load leveling kits,
air shocks, or modifications that change axle-to-frame distance will
provide a false reading to valve. False readings may result in
unsatisfactory brake performance. |
