Air Brake System - freightliner M2 Plus 2023 Manual

Brake Systems

Air Brake System

A dual air brake system consists of two independent
air systems that use a single set of brake controls.
Each system has its own reservoirs, plumbing, and
brake chambers. The primary system operates the
service brakes on the rear axle; the secondary
system operates the service brakes on the front axle.
Service brake signals from both systems are sent to
the trailer.
WARNING
Do not operate the vehicle with the front brakes
backed off or disconnected. Backing off or
disconnecting the front brakes will not improve
vehicle handling and may lead to loss of vehicle
control, resulting in property damage or personal
injury.
Air Brake System, General
Information
The warning light and buzzer come on if air pressure
drops below 64 to 76 psi (441 to 524 kPa) in either
system. If this happens, check the dual system air
pressure gauge to determine which system has low
air pressure. Although the vehicle's speed can be
reduced using the brake pedal, either the front or
rear service brakes do not operate at full capacity,
causing a longer stopping distance. Bring the vehicle
to a safe stop and have the air system repaired
before continuing.
IMPORTANT: In the event of a total loss of
service brakes with full system air pressure, use
the parking brake control valve (yellow knob) to
bring the vehicle to a complete stop in the
safest location possible.
Before a vehicle with insufficient system air pressure
can be moved, the spring parking brakes must be
released by applying an external air source at the
gladhands, or by manually caging the spring parking
brakes.
WARNING
Do not cage the spring parking brakes and then
drive the vehicle. There would be no means of
stopping the vehicle, which could result in
serious personal injury or vehicle damage.
Before caging the spring parking brakes, make
11.1
the connection to a towing vehicle or chock the
tires.
After correcting the brake system problem, uncage
the spring parking brakes before resuming normal
vehicle operation.
Primary Air Brake System
Loss of air pressure in the primary air system causes
the rear service brakes to become inoperative. The
secondary air system continues to operate the front
brakes and the trailer brakes (if equipped).
Secondary Air System
Loss of air pressure in the secondary air system
causes the front axle brakes to become inoperative.
The primary air system continues to operate the rear
service brakes and the trailer brakes (if equipped).
Air Brake System Operation
Before driving your vehicle, allow time for the air
compressor to build up a minimum of 100 psi (689
kPa) pressure in both the primary and secondary
systems. Monitor the air pressure system by
observing the dual system air pressure gauge and
the low-air-pressure warning light and buzzer. The
warning light and buzzer shut off when air pressure
in both systems reaches 64 to 76 psi (441 to 524
kPa).
IMPORTANT: Before driving the vehicle, secure
all loose items in the cab so that they do not
shift forward during a full brake application.
Make sure all passengers are wearing seat
belts.
During normal brake stops, depress the brake pedal
until braking action slows down the vehicle. Increase
or decrease the pressure on the pedal so that the
vehicle comes to a smooth, safe stop. Apply the
parking brake if the vehicle is to be parked.
IMPORTANT: An air brake proportioning system
may be used in tractor air brake systems when
the vehicle is not equipped with antilock braking
system (ABS). When operating in bobtail mode,
the rear brake chambers (on which the axle
load has been greatly reduced) receive reduced
(proportional) air pressure, while the front axle
brake chambers receive full (normal) air
pressure. This results in a different brake pedal
"feel," as the pedal seems to require more travel
and/or effort to slow or stop the vehicle.