© 2020 Pierce Manufacturing Inc. All Rights Reserved. Driving the Vehicle / 5-57
OPERATION
5-30. Auxiliary Braking System
An Auxiliary Brake System provides braking torque through the driveline to the rear wheels. The use of an auxiliary
brake reduces brake wear, reduces brake heat buildup, and can help to minimize the occurrence of brake fade
during heavy or frequent braking.
An Electronic Control Unit (ECU) in the Antilock Braking System (ABS) monitors the wheels and turns off the
auxiliary brake if it senses that the wheels are not spinning at the same speed. The ABS ECU does not know to turn
off the auxiliary brake until an ABS event has already occurred. In the split second between the ABS sensing the
skid and the time it takes for the auxiliary brake to shut off, there may be a skid initiated. For this reason, Pierce
Manufacturing recommends turning off the Auxiliary Brake System during slippery conditions.
5-30.1 Compression Brake
The compression brake (Jake Brake
®
or equivalent) is an electronically actuated mechanical system added to the
engine valve train. When activated, the compression brake alters the operation of the engine’s exhaust valves so
that the engine works as a power-absorbing air compressor.
5-30.2 Exhaust Brake
The exhaust brake (Extarder
®
, Blue-Ox
®
, or equivalent) consists of a flapper valve installed in the exhaust pipe
between the engine and the muffler. When activated, the flapper restricts the passage of the exhaust gases and
increases the back pressure in the cylinders during the exhaust stroke. This increases the natural retardation effect
of the engine. Braking torque at the wheels will vary depending on the transmission range selected.
5-30.3 Electromagnetic Retarder
The electromagnetic retarder (Telma
®
or equivalent) may be mounted in the driveline or attached directly to the rear
axle. When activated, electrical power is supplied to a series of coils in the retarder that create an electromagnetic
field. This field inhibits the rotation of the rotor and creates a braking torque at the rear wheels. Various options allow
the retarder to be applied in stages either manually or by combinations of brake and accelerator pedal settings. Heat
generated by the retardation effect is dissipated by cooling fins on the retarder.
The use of any compression brake or exhaust brake systems during slippery road conditions or
inclement weather may cause rear wheel lock-up and loss of vehicle control, resulting in property
damage, personal injury, or death.
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