SERVICE REPAIR
H1.50XM H1.75XM H2.00XMS Europe [D001]
1
INTRODUCTION
GENERAL
This section has a description and the service
procedures for the parts of the brake system. The brake
system includes the following parts: master cylinder,
brake shoes, wheel cylinders, an inching/brake pedal
and linkage, and the parking brake system. A
troubleshooting section is included at the end of this
section.
DESCRIPTION AND OPERATION
Service Brake
The master cylinder has a housing, a piston with two
ring cups, a return spring and a check valve assembly.
The reservoir for the fluid is separate from the master
cylinder. When the brake pedal is pushed, the push rod
moves the piston assembly. The primary cup forces the
brake fluid through the check valve to the wheel cylin-
ders. The secondary cup keeps the fluid that is above the
primary cup in the master cylinder.
When the brake pedal is released, the return spring
pushes the piston assembly back against the retainer
washer. The return springs for the brake shoes force the
fluid that is in the wheel cylinders back through the lines
to the check valve. The pressure in the lines moves the
check valve from its seat. The fluid flows around the
check valve to the master cylinder bore.
When the brake pedal is released quickly, the return
spring moves the piston faster than the brake fluid can
flow around the check valve. To prevent cavitation,
holes are drilled in the piston. Fluid from the inlet port
flows through the holes. The fluid bends the lip of the
primary cup and permits fluid to enter the pressure
chamber.
The check valve assembly permits fluid from the pres-
sure chamber to flow to the lines when the brake pedal is
pushed. When the pressure in the pressure chamber is
greater than pressure in the lines, the check valve will
open. When the brake pedal is released, the pressure in
the lines is greater than the pressure in the pressure
chamber. The check valve assembly then moves against
the spring pressure to pe