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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

1 2 3 4 5 6 ... 15 16

Inhaltsverzeichnis

Seite 1 - SD-20-6608

1®Bendix® A2LS™ Hydraulic Drum Brakes w/ParkingSD-20-6608FIGURE 1 - A2LS™ AUTOMATIC ADJUSTING TWO LEADING SHOE DRUM BRAKEWHEEL CYLINDERWHEEL CYLINDER

Seite 2 - PARKING BRAKE APPLICATION

10FIGURE 20 - EXPANDER WEDGENote: Normal wear pressure marks should not be mistakenfor scoring. Some discoloration of the piston diametermay be appare

Seite 3

11FIGURE 22 - PISTON ADJUSTERFIGURE 23 - NEW AND OLD STYLE PISTON AND OVERRIDEWHEELinsert the assembly into the bore of the housing until itengages th

Seite 4 - PREVENTIVE MAINTENANCE

122. Lubricate the adjuster shaft with DOT 4 brake fluid andscrew the adjuster shaft fully into the piston assembly,then unscrew one full turn, Figure

Seite 5 - PERSONAL INJURY OR DEATH:

13RED - Park brake expander end on both LH and RH brakes.GREEN - Wheel cylinder end on LH brakes.YELLOW - Wheel cylinder end on RH brakes.2. Remove th

Seite 6

14DRUM BRAKE TROUBLESHOOTINGSYMPTOM CAUSE REMEDY1. Low Pedal. 1. Excessive clearance between 1. Adjust brakes.drums and linings.2. Automatic adjusters

Seite 7 - UNIT REMOVAL

15DRUM BRAKE TROUBLESHOOTINGSYMPTOM CAUSE REMEDY6. Scored, hard spotted or out of 6. Refinish or replace drums inround drums. axle sets.7. Rough or co

Seite 8 - DISASSEMBLY

16DRUM BRAKE TROUBLESHOOTINGSYMPTOM CAUSE REMEDY9. One brake drags. 1. Weak or broken shoe return 1. Replace shoe return springs.spring.2. Improper br

Seite 9 - CLEANING AND INSPECTION

2FIGURE 2 - SERVICE BRAKE APPLICATIONINPUT/TAPPETPISTONWHEELCYLINDERPISTONSROLLER/TAPPETPISTONABUTMENTTAPPETWHEELCYLINDERPISTONSFIGURE 5 - PARKING BRA

Seite 10 - ASSEMBLE EXPANDER UNIT

3FIGURE 7 - ADJUSTER OPERATIONforward, the wedge rollers force the expander abutment tappetand roller tappet/piston apart, Figure 5, and directly, ort

Seite 11 - ASSEMBLE WHEEL CYLINDER UNIT

4FIGURE 9 - ADJUSTER OPERATIONFIGURE 8 - ADJUSTER OPERATIONoff its seat in the cylinder body. If the movement of theadjuster shaft helix through the a

Seite 12 - BRAKE SHOE INSTALLATION

5FIGURE 10 - REAR VIEW OF THE BACKING PLATE(DIRTSHIELD)CITY DELIVERYEvery 15,000 miles (24,000 km), two months, or 300operating hours, whichever occur

Seite 13 - FINAL CHECK

6FIGURE 13FIGURE 12 - SHOE RETURN SPRING REMOVALFIGURE 11 - ADJUSTING ADJUSTER MECHANISMREMOVALBRAKE SHOE REMOVALThe removal, disassembly, cleaning an

Seite 14 - DRUM BRAKE TROUBLESHOOTING

74. Place the recessed end of a 3/8 inch (9,53 mm) squaredrive socket extension over the end of the wheel cylinderend shoe return spring, Figure 12. T

Seite 15

8DISASSEMBLYBRAKE SHOESBendix brake shoes and linings are available as sets withnew factory lining installed. If the brake shoes are in goodcondition,

Seite 16

92. Remove the tappet head and manual override assemblyfrom the wheel cylinder body, Figure 15. Separate thetappet head from the manual override wheel