OPERATOR'S MANUAL

USING THE BRAKE SYSTEM STARTING AND OPERATING THE VEHICLE
– 122 – Y53-6027
Medium Duty (R05/09)
NOTE: Today’s diesel electronic engines have
significant torque and startability power at low
RPM. Combinations of engine speed and avail-
able torque may over-power the vehicle’s parking
brakes.
WARNING! The brake system is a critical vehi-
cle safety system. For the safety of you and
others around you, have the vehicle submitted
for periodic preventive maintenance checks
as well as having any suspected problems
immediately checked by an Authorized Ser-
vice Center. Failure to properly maintain your
brake system can lead to accident, resulting
in death or personal injury
Brake Components
The following is a brief description of the hydraulic brake
system. It is intended to supply you with general informa-
tion on how the system works. For complete information
see the Peterbilt Medium Duty Maintenance Manual.
Anti-Lock Brake System (ABS) Modulator Valve Body:
adjusts brake fluid flow between the master cylinder and
the wheel calipers to avoid wheel lockup.
ABS Warning Lamp: lights when the ABS controller
detects wheel lock-up while driving and activates the ABS.
Lights also when a fault in the ABS is detected.
Brake Fluid Reservoir: stores brake fluid and offers a
place to replenish when needed.
Brake Master Cylinder: translates brake pedal force into
hydraulic fluid pressure in the primary and secondary cir-
cuits.
Brake Pedal: applies actuation force from operator's foot
to the master cylinder pistons.
Brake Warning Lamp: illuminates when either power
steering fluid flow is interrupted or when a pressure differ-
ential is present in the primary and secondary brake fluid
pressure. Either case adversely affects braking operation.
Differential Switch: measures the hydraulic fluid pres-
sure difference between the primary and secondary cir-
cuits.