freightliner BUSINESS CLASS M2 Driver Manual page 122

Steering and Brake Systems
the trailer brakes would release, possibly causing
an unattended runaway vehicle.
NOTICE
Never apply the service and spring parking
brakes simultaneously. To do so transmits exces-
sive input force to the brake components, which
could damage or cause eventual failure of brake
actuating components.
Brake Controls
The trailer brake lever (hand control valve) is used
for applying the trailer brakes without applying the
truck or tractor service brakes. It is usually mounted
on the right-hand control panel. See
valve can be partially or fully applied, but in any par-
tially applied position, it will be overridden by a full
application of the brake pedal. Moving the lever
down applies the trailer brakes, while moving it up
releases the trailer brakes. The lever will automati-
cally return to the up position when it is released.
WARNING
Do not use the trailer service brakes for parking;
they are not designed for this purpose. If air
bleeds out of the trailer air tank during parking,
the vehicle could roll, causing serious personal
injury or property damage.
10/17/2001
Fig. 9.2, Trailer Brake Lever
The red octagonal-shaped knob in the control panel
actuates the trailer air supply valve. See
After the vehicle's air hoses are connected to a
trailer and the pressure in both air systems is at least
9.3
65 psi (448 kPa), the trailer air supply valve must be
pushed in. It should stay in to charge the trailer air
supply system and to release the trailer spring park-
ing brakes.
Pull the trailer air supply valve out before disconnect-
ing a trailer or when operating a vehicle without a
trailer. If pressure in both air systems drops to 35 to
45 psi (242 to 310 kPa), the trailer air supply valve
automatically pops out, exhausting the trailer air sup-
ply, and applying the trailer service or spring parking
brakes.
Fig. 9.2. The
03/10/99
The yellow diamond-shaped knob in the control
panel actuates the parking brake valve. See
Pulling out the parking brake valve applies both the
tractor and trailer parking brakes and automatically
causes the trailer air supply valve to pop out.
Do not use the spring parking brakes if the ser-
vice brakes are hot, such as after descending a
steep grade. To do so could damage the brakes.
Allow hot brakes to cool before using the spring
parking brakes.
Do not use the spring parking brakes during
freezing temperatures if the service brakes are
wet. To do so could cause them to freeze. If the
brakes are wet, drive the vehicle in low gear and
f610591 lightly apply the brakes to heat and dry them.
If the trailer is not equipped with spring parking
brakes, pulling out the parking brake valve applies
the tractor parking brake and the trailer service
Fig. 9.3.
brakes. When the tractor and trailer parking brakes
(or trailer service brakes) are both applied, the trailer
1
1. Trailer Air-Supply-Valve Knob
2. Parking-Brake-Valve Knob
Fig. 9.3, Brake Valve Knobs
NOTICE
2
f610291
Fig. 9.3.