Volvo VNL 780 Operator's Manual page 329

If the brakes are wet, drive the vehicle in low gear and lightly apply the brakes to heat and
dry them. Allow hot brakes to cool before using the parking spring brakes.
There are several ways to determine if the parking brakes have been set. By pulling out
the yellow knob:
•
An audible rush of air will be heard when the parking brake knob is pulled. The air
exhausts from the park brake valve itself and from the spring brake chambers on the
rear axle(s).
•
A black ring around the base of the yellow control knob will be seen.
•
The engine will stall if an attempt is made to set the vehicle in motion.
•
There will be a fluctuation in the air pressure gauge needles.
•
The knob cannot be pulled out any further.
DANGER
DO NOT attempt in any way to
disassemble or tamper with the spring
brake chamber. The force stored in the
spring, if suddenly released, can cause
serious personal injury or death.
DANGER
DO NOT apply the parking brake while
the vehicle is moving. The rear wheels
may lock up causing loss of vehicle
control leading to an accident, personal
injury or death.
OPERATION 319