Peterbilt Medium Duty Truck Owner's Manual - Peterbilt Motors

USING THE BRAKE SYSTEM
WARNING! Efficiency of emergency braking
depends on the amount of air available in the
front circuit reservoir, which is sufficient for a
limited number of brake applications and
releases.
• REMEMBER: when the remaining system
pressure drops below 60 psi (414 kPa), the
spring brake is automatically applied, stopping
the vehicle abruptly, potentially causing
death or serious injury. Observe the
warning light (BRAKE AIR) in the panel, it
will come on before the spring brakes are
applied. If it comes on, do not continue to
drive the vehicle until it has been properly
repaired or serviced.
Brakes — Tractor/Trailer
The following applies to tractor/trailer configurations:
If pressure is lost in the tractor front or rear circuit, the
“check” valves isolate the unaffected circuit, allowing this
circuit to continue normal operation. The trailer brakes are
still functional.
STARTING AND OPERATING THE VEHICLE
• If air pressure is lost in the trailer supply/park circuit,
and the pressure drops below 60 psi (414 kPa), the
trailer spring brakes are automatically applied, and
the tractor air pressure circuits are unaffected.
• If air pressure is lost in the trailer brake service circuit,
and the pressure in the tractor front and rear circuits
drops below 60 psi (414 kPa), the tractor and trailer
spring brakes are automatically applied.
Emergency Braking
WARNING! Unless you have an anti-lock
braking system, always avoid completely
depressing the service brake pedal, if possible,
even during emergency braking.
Depressing the brake pedal too aggressively
can cause the wheels to lock, which can lead
to an uncontrolled skid and can result in an
accident involving death or personal injury.
For Non-ABS Vehicles: To stop your vehicle in an emergency,
vary the service brake application pressure to provide
maximum braking force without locking the wheels.
– 112 – Y53-6027 Medium Duty (R05/09)