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

Operating Instructions
On tractors that do not have anti-lock brake systems (ABS) a
bobtail brake proportioning system is installed. When a trailer
is not connected (bobtail mode), the brake application pressure
(on the rear drive axle) will automatically be limited by
the proportioning system.
Engine Retarder (option)
An engine retarder or exhaust brake may be installed (as an
option) to create a braking effect on the drive wheels. This
device uses your engine's power to slow your vehicle down.
Because it can help keep your vehicle's brakes from overheating,
it can save wear and tear on the service brakes.
However, the retarder is not an emergency brake.
Ideally (on normal road surfaces), you should slow your vehicle
with the retarder (where permitted by law) and use the
service brakes only for stopping completely. Operating this
way will greatly prolong the life of the brakes.
Using the Brake System
WARNING! The service brakes must be used in
an emergency. The engine or retarder alone
might not stop you fast enough to prevent an
accident. You could be badly hurt if you relied
only on the engine retarder.
• The engine retarder is NOT intended as the primary
brake for the vehicle, nor is it an emergency brake.
The engine retarder only helps the service brakes by
using pressure to slow the drivetrain. Use the service
brakes for quick stops.
Exhaust Brake
With the exhaust brake switch ON, the brake automatically
creates its braking effect when you remove your foot from the
accelerator pedal.
The brake switch is located on the accessory dash panel. It
controls whether the brake is ON (ready to slow the vehicle
down) or OFF (no braking action).
• 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.
• Make sure the brake is OFF before starting the engine.
Medium Duty (R10/06) Y53-6008 – 85 –