Bendix Commercial Vehicle Systems A2LS HYD DRUM BRAKES W/PARKING 2/08 - Manual

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Bendix ® A2LS ™ Hydraulic Drum Brakes w/Parking
SD-20-6608
FIGURE 1 - A2LS ™ AUTOMATIC ADJUSTING TWO LEADING SHOE DRUM BRAKE
WHEEL CYLINDER
WHEEL CYLINDER END
SHOE RETURN SPRING
GROMMETS
CAP SCREWS
SHOE HOLD-DOWN CLIP (NOT
FITTED TO EARLY BRAKES)
DIRT SHIELD
CROSS-OVER
PIPE
GASKET
EXPANDER END SHOE
RETURN SPRING
DESCRIPTION
The A2LS ™ drum brake is a hydraulically operated duo-duplex
brake with an automatic adjustment and parking brake
feature. The A2LS
™ drum brake (automatic adjust, two
leading shoes) provides two leading shoes in either direction
of drum rotation and an automatic adjustment of the brake
shoes to compensate for lining wear.
Both the wheel cylinder unit and expander unit have cast
integral brake mounting lugs, each taking the brake torque
load. The wheel cylinder unit contains two single acting
hydraulic cylinders with automatic adjusters. The expander
unit contains a double acting hydraulic cylinder with a park
brake wedge expander. Wheel cylinder and expander units
have either a 1-5/8 inch (41,3mm) or 1-3/4 inch (44,5mm)
diameter bore depending upon vehicle brake requirements.
The units are hydraulically connected together with a bridge
pipe or crossover tube.
The single web brake shoes are located by slots in the wheel
cylinder tappet head, the expander input tappet/piston and
abutment tappet, and are retained by the shoe return springs.
As with all Bendix automatic adjusting brakes, provision is
made for manual override of the automatic adjuster. This
should only be needed for initial adjustment of the shoes to
a specific drum clearance, or to back off shoes to enable a
lipped drum to be removed.
The brake assembly incorporates an integral backing plate
(dirtshield) to protect the brake from excessive water and
dirt intrusion. The backing plate (dirtshield) contains a steady
post for each brake shoe to insure that lining material is
kept parallel to the drum braking surface. Both brake shoes
are free to slide on their abutment faces against the backing
plate (dirtshield) and are therefore able to centralize
themselves to the drum. Lining material is 3/4 inch (19,11
mm) thick in the center of the shoe tapering to approximately
5/8 inch (15,9 mm) at each end. Lining inspection holes and
CROSS-OVER PIPE
RETAINING SPRING
EXPANDER