Medium Duty Operator's Manual - Peterbilt Motors Company
Medium Duty Operator's Manual - Peterbilt Motors Company
Medium Duty Operator's Manual - Peterbilt Motors Company
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USING THE BRAKE SYSTEM<br />
WARNING! Do not use an engine retarder<br />
when you are driving bobtail or with an<br />
unloaded trailer. Using engine retarders while<br />
bobtailing or with an unloaded trailer can<br />
cause a wheel lockup resulting in less control<br />
and/or jackknife. The trailer may not load the<br />
rear tractor tires enough to provide necessary<br />
traction. When you are bobtail or unloaded,<br />
you can have a serious accident if your<br />
wheels lock suddenly during braking—you<br />
could be severely injured.<br />
Bobtail Brake Proportioning System<br />
When a trailer is not connected, the drive axle brake application<br />
pressure will automatically be limited by the proportioning<br />
system.<br />
The brake proportioning system regulates the application<br />
pressure to the rear drive axle. To provide equivalent braking<br />
power, tractors (driven bobtail) will require greater<br />
brake pedal application than other types of vehicles not<br />
equipped with a proportioning system.<br />
STARTING AND OPERATING THE VEHICLE<br />
On tractors that do not have anti-lock brake systems<br />
(ABS) a bobtail brake proportioning system is installed.<br />
When a trailer is not connected (bobtail mode), the brake<br />
application pressure (on the rear drive axle) will automatically<br />
be limited by the proportioning system.<br />
Engine Retarder (option)<br />
An engine retarder or exhaust brake may be installed (as<br />
an option) to create a braking effect on the drive wheels.<br />
This device uses your engine's power to slow your vehicle<br />
down. Because it can help keep your vehicle's brakes<br />
from overheating, it can save wear and tear on the service<br />
brakes. However, the retarder is not an emergency brake.<br />
Ideally (on normal road surfaces), you should slow your<br />
vehicle with the retarder (where permitted by law) and use<br />
the service brakes only for stopping completely. Operating<br />
this way will greatly prolong the life of the brakes.<br />
– 114 – Y53-6008A <strong>Medium</strong> <strong>Duty</strong> (R05/09)