Troubleshooting guide

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ABS — Antilock Brake System. ABS electronically monitors
wheel speed and helps stopping ability by preventing wheel
lock-up by rapidly applying the brakes during stops.
ABS Event — A situation that causes the ABS controller to
intervene and activate the modulator valve(s).
ABS Indicator Lamp — An indicator lamp which shows
the status of an antilock system. When the indicator lamp is
illuminated (amber), ABS is disabled and the vehicle reverts to
ordinary brake operation without the benefi ts of ABS braking.
Actuate — To cause the mechanical action (or motion) of a
brake system component.
Actuator — A wheel-end device which converts air pressure
into mechanical force.
Air build-up — The part of the compressor cycle concerned
with building (increasing) pressure in the brake system air tanks
to a predetermined maximum level (typically 110-130 psi).
Air compressor — Engine-driven pump that compresses air
to pressurize the air system reservoirs.
Air compressor cut-in — Predetermined setting at which the
air governor starts the compression of air by the compressor.
Air compressor cut-out — Predetermined setting at which the
air governor stops the compression of air by the compressor.
Air disc brake — Air-actuated brakes that cause a caliper to
clamp a rotor between two brake pads to slow the vehicle.
Air dryer — An in-line fi ltration system that removes both
water vapor and oil droplets from the compressor discharge air
after it leaves the compressor.
Air gauge — Dash-mounted gauge showing air pressure [in
pounds per square inch (psi)].
Air system balance — Has two different aspects: pressure-
level balance and timing balance. Air system balance deals
primarily with the system design and arrangement of vehicle
air system components (e.g. foot brake valve, quick release
valves, and relay valves) that directly control the actuation of
the service brakes during normal stops. For timing balance -
see Pneumatic Timing Balance.
Air tank — See Reservoir.
Anti-compounding — A system that prevents the application
of service brakes from compounding (adding to) the force
exerted by the parking brakes.
Antilock — See ABS.
ASR — Automatic Slip Regulation. Another name for traction
control. See TCS - Traction Control Systems.
ATC — Automatic Traction Control. An optional system that
is available on 4- and 6-channel ABS systems. Automatic
traction control minimizes wheel slipping during acceleration
by controlling both the engine throttle and brake pressures at
individual wheels as needed.
Brake balance — When all brakes — on all axles — do their
fair proportion of the work of slowing the vehicle. The factors
going into the brake balance include: pneumatic, thermal,
timing, force, and wear.
Brake block — The friction material, or lining, used on brake
shoes. Disc brakes use pads with friction material.
Brake chamber — Converts air pressure being applied to a
mechanical force, via a push rod, for foundation brake actuation.
It may consist of service chamber, or service chamber and
spring chamber combination. For example: A 24/30 chamber
consists of a Type 24 service chamber and a Type 30 spring
chamber. See Service brake/Spring brake.
Brake chamber diaphragm — A bellows-type device within
brake chamber that converts air pressure to mechanical force
via a push rod. The size of the brake chamber correlates
with the effective area of the diaphragm. A Type 24 chamber
diaphragm has an approximate effective area of 24 square
inches.
Brake drag — Either a constant, or intermittent, failure of one
or more brakes to release immediately and/or completely after
a driver removes his foot from the brake treadle.
Brake drum — Attached to the axle hub assembly, the brake
drum absorbs kinetic energy from the brake shoe and lining
assembly and transfers heat away from the brake surface to
dissipate the heat into the atmosphere over time.
Brake fade — Typically brake fade involves a reduction in
braking force experienced on drum brakes when applied on
a long grade. Maladjusted brakes may cause an overheated
drum to expand to the degree that the push rod travel is
insuffi cient to fully actuate the brakes. Heat fade can occur
when linings overheat and become less aggressive. Gradual
and predictable fade is desirable as a warning.
Brake pedal — The suspended mechanical means of actuating
a foot brake control valve.
Brake proportioning — An optional feature that ratios the
brake application pressure in accordance with the loading of an
axle set. "Bobtail proportioning," similarly limits the drive-axle
brake pressure when a tractor is operated “bobtail” (without a
trailer).
Brake treadle — The mechanical means of actuating a fl oor-
mounted foot brake control valve.
Breakaway valve
— See Tractor protection valve.
Glossary