Peterbilt Medium Duty Trucks Operator's Manual after 1-07

Using the Brake System
To operate the trailer brake hand valve:
• Pull down on the lever.
• The valve is self-returning. When pressure is removed
from the valve lever, it will return to the OFF position.
NOTE: The trailer brake is not to be used as a substitute
for the service brakes. Using this brake frequently,
instead of using the foot brake, will cause
the trailer brakes to wear out sooner.
WARNING! Do not use the trailer hand brake or
service brakes to park and hold an unattended
vehicle—use the parking brakes. Because service
brakes work with air pressure, these brakes
could slowly release. Your vehicle could roll,
causing a serious accident. Someone could be
hurt or killed. Never rely on the service brakes to
hold a parked vehicle.
Driving Bobtail or With an Unloaded Trailer
NOTE: The following information is applicable only
to tractor configurations.
Operating Instructions
Do not use the engine retarder (such as an exhaust brake) to
slow the vehicle down when you are bobtailing or pulling an
empty trailer.
WARNING! Do not use an engine retarder when
you are driving bobtail or with an unloaded
trailer. Using engine retarders while bobtailing
or with an unloaded trailer can cause a wheel
lockup resulting in less control and/or jackknife.
The trailer may not load the rear tractor tires
enough to provide necessary traction. When you
are bobtail or unloaded, you can have a serious
accident if your wheels lock suddenly during
braking—you could be severely injured.
Bobtail Brake Proportioning System
When a trailer is not connected, the drive axle brake application
pressure will automatically be limited by the proportioning
system.
The brake proportioning system regulates the application
pressure to the rear drive axle. To provide equivalent braking
power, tractors (driven bobtail) will require greater brake
pedal application than other types of vehicles not equipped
with a proportioning system.
– 84 – Y53-6008 Medium Duty (R10/06)