1
Bendix
®
ADB 22X
™
, ADB 225
™
, SN6
™
, SN7
™
, SK7
™
Air Disc Brakes
SD-23-7541
DESCRIPTION
Bendix
®
Air Disc Brakes use a floating caliper design to
provide foundation braking on all axles of heavy commercial
vehicles, buses and trailers. Bendix Air Disc Brakes
provide safety and performance, as well as ease of service.
Available in models with or without a combination spring
brake unit, these brakes may also include optional wear
sensors and/or wear diagnostic equipment.
OPERATION
Bendix Air Disc Brakes convert air pressure into braking
force. (See Figure 2.) When the vehicle brakes are
applied, air enters the service brake chamber through
the supply port, applying pressure within the diaphragm.
The pressure expands the diaphragm, applying force to,
and moving the pressure plate and pushrod forward. The
pushrod acts against a cup in the internal lever which
pivots on an eccentric bearing moving the bridge. Moving
against a return spring, the bridge transfers the motion to
two threaded tubes and tappets, which move the inner
brake pad. The inner brake pad (from its normal position of
having a running clearance between it and the rotor) moves
into contact with the brake rotor. Further movement of the
bridge forces the caliper, sliding on two stationary guide
pins, away from the rotor, which pulls the outer brake pad
into the rotor. The clamping action of the brake pads on
the rotor applies braking force to the wheel.
Brake Release and Adjustment
When the vehicle brakes are released, the air pressure
in the service brake chamber is exhausted and the return
springs in the chamber and the bridge return the air disc
brake to a neutral, non-braked position. To maintain the
running clearance gap between the rotor and the brake
pads over time, the non-braked position is mechanically
adjusted by a mechanism in the caliper. The adjustment
mechanism operates automatically whenever the brakes
are activated, to compensate for rotor and brake pad wear
and to keep the running clearance constant. During pad
or rotor maintenance, the technician manually sets the
system’s initial non-braked position. The total running
clearance (sum of clearances on both sides of the rotor)
should be between 0.024 to 0.043 in. (0.6 and 1.1 mm).
FIGURE 1 - BENDIX
®
ADB 22X
™
AIR DISC BRAKE
FIGURE 2 - CROSS-SECTION VIEW SHOWING BRAKE
OPERATION
Supply Port
Return Spring
Pushrod
Lever
Outer Brake
Pad
Inner Brake Pad
Rotor
Eccentric Bearing
Service Brake
Chamber
Bridge
Pressure
Plate
Diaphragm
