freightliner PX113064S T 2016 Manual Download

Page: 149 / 236

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.

The red octagonal-shaped knob in the control panel
actuates the trailer air supply valve. See

Fig. 11.12

After the vehicle’s air hoses are connected to a
trailer and the pressure in both air systems is at least
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
parking brakes.

Pull the trailer air supply valve out before
disconnecting a trailer.

If pressure in both air systems drops to 20 to 45 psi
(138 to 310 kPa), the red trailer air supply valve and
yellow parking brake valve automatically pop out,
applying both the tractor and trailer spring parking
brakes. If the trailer is not equipped with spring
parking brakes, the trailer service brakes are applied.

The yellow diamond-shaped knob in the control
panel actuates the parking brake valve. See

Fig. 11.12

. Pulling out the parking brake valve

applies both the tractor and trailer spring parking
brakes and automatically causes the trailer air supply
valve to pop out. Pushing in the parking brake valve
releases the tractor parking brakes.

NOTICE

Do not use the spring parking brakes if the
service 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
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
brakes. When the tractor and trailer parking brakes
(or trailer service brakes) are both applied, the trailer
brakes are released by pushing in the trailer air
supply valve, leaving the tractor parking brake
applied. Air pressure in the primary or secondary
reservoir must be at least 65 psi (448 kPa) before
the tractor spring parking brakes, or the trailer
service or spring parking brakes, can be released.

Automatic Slack Adjusters

Automatic slack adjusters should never be manually
adjusted except during routine maintenance of the
foundation brakes (such as replacing shoes), during
slack adjuster installation, or in an emergency
situation.

When the brake pushrod stroke exceeds the legal
brake adjustment limit on a vehicle, there is likely a
mechanical problem with the foundation brake
components or the adjuster is improperly installed.

Visit a repair facility as soon as possible when
brakes equipped with automatic slack adjusters are
determined to be out of adjustment.

f610591

02/03/2017

Fig. 11.11, Trailer Brake Lever

f610291

02/02/2017

Trailer Air Supply Valve Knob

Parking Brake Valve Knob

Fig. 11.12, Brake Valve Knobs

Brake Systems

11.6