BENDIX A2LS HYD DRUM BRAKES W-PARKING Manual
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BENDIX A2LS HYD DRUM BRAKES W-PARKING Manual

BENDIX A2LS HYD DRUM BRAKES W-PARKING Manual

Hydraulic drum brakes w/parking
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®
®
™
Bendix
A2LS
WHEEL CYLINDER END
SHOE RETURN SPRING
EXPANDER END SHOE
RETURN SPRING
WHEEL CYLINDER
EXPANDER
FIGURE 1 - A2LS
™
AUTOMATIC ADJUSTING TWO LEADING SHOE DRUM BRAKE
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.
Hydraulic Drum Brakes w/Parking
GASKET
DIRT SHIELD
SHOE HOLD-DOWN CLIP (NOT
FITTED TO EARLY BRAKES)
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
CROSS-OVER
PIPE
CAP SCREWS
GROMMETS
1

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Summary of Contents for BENDIX A2LS HYD DRUM BRAKES W-PARKING

  • Page 1 As with all Bendix automatic adjusting brakes, provision is feature. The A2LS ™ drum brake (automatic adjust, two made for manual override of the automatic adjuster.

  • Page 2: Operation

    manual override access holes are covered by rubber (ARROW INDICATES DIRECTION OF DRUM ROTATION) grommets. INPUT/ TAPPET PISTON TORQUE TORQUE WHEEL LOAD LOAD CYLINDER PISTONS WHEEL ROLLER/TAPPET FIGURE 4 - REVERSE DRUM ROTATION CYLINDER PISTON PISTONS When the brake shoe lining contacts the drum the shoes ABUTMENT TAPPET are forced around, sliding on the abutments, in the direction...
  • Page 3 PISTON MANUAL OVERRIDE DRIVE RING WHEEL ADJUSTER SPRING SEAL SHAFT HELIX ADJUSTER DRIVE RING FIGURE 6 - WHEEL CYLINDER ASSEMBLY CUT-AWAY The adjuster drive ring is held in light contact with its seat in forward, the wedge rollers force the expander abutment tappet the cylinder body by the drive ring spring.

  • Page 4: Important! Please Read

    As the axial tolerance between the adjuster shaft helix and BRAKE APPLICATION BRAKES HELD ON (DRIVE RING (ADJUSTMENT REQUIRED) ALREADY SETTLED IN NEW adjuster drive ring is taken up, the load on the drive ring POSITION) DRIVE RING-LIFTED OFF SEATING-ROTATES RIDES helix forces it onto its seat.

  • Page 5: Service Checks

    4. Check all hydraulic fittings and the surface of the all precautions pertaining to use of those tools. backing plate (dirtshield) for any evidence of hydraulic ® 9. Use only genuine Bendix replacement parts, fluid leakage. components and kits. 5. Refer to the vehicle manual for service checks of other A.

  • Page 6: Brake Shoe Removal

    Damage to some parts may occur as a result of disassembly. Maintenance kits are available from your local authorized Bendix parts outlet. 1. Park the vehicle on a level surface and prevent vehicle movement by a means other than with the parking brake.
  • Page 7 10. Inspect the wheel cylinder unit and expander unit for leaks. Lift the dust boots at their inner diameters from the tappets and pistons. If fluid escapes when the dust boots are lifted, the wheel cylinder or expander must be removed for service.
  • Page 8 DISASSEMBLY BRAKE SHOES Bendix brake shoes and linings are available as sets with new factory lining installed. If the brake shoes are in good SPRING condition, neither worn nor bent, new lining may be installed on the old brake shoes. For lining installation procedures, and brake shoe inspection procedures, refer to Bendix publication;...

  • Page 9: Cleaning And Inspection

    2. Remove the tappet head and manual override assembly Clean all rubber parts that are to be reused with clean DOT from the wheel cylinder body, Figure 15. Separate the 4 heavy duty brake fluid. Place on clean sheet of paper to tappet head from the manual override wheel.
  • Page 10 If there Use all of the parts supplied in the Bendix repair kit to replace is any doubt as to the condition of the cylinders, new the old parts removed from the cylinders.
  • Page 11 Shoe Adjustment in this manual. ASSEMBLE WHEEL CYLINDER UNIT Use all of the parts supplied in the Bendix repair kit to replace the old parts removed from the cylinder. 1. Lubricate the piston seal, Figure 15, with new DOT 4 brake fluid and install the seal onto the piston with the lip facing inwards, Figure 21.

  • Page 12: Brake Shoe Installation

    Note: A new design piston may be used to replace the piston LEFT HAND in older style brakes but the override wheel must also BRAKE ASSEMBLY be changed. Although it would be permissible to fit an old style piston into a new style brake, it would be a GREEN ON LH RED ON LH &...

  • Page 13: Brake Shoe Adjustment

    RED - Park brake expander end on both LH and RH brakes. 6. Rotate each wheel to insure that the hydraulic system has fully released parking brakes. GREEN - Wheel cylinder end on LH brakes. 7. Apply parking brake and check that the wheels cannot YELLOW - Wheel cylinder end on RH brakes.
  • Page 14 DRUM BRAKE TROUBLESHOOTING SYMPTOM CAUSE REMEDY 1. Low Pedal. 1. Excessive clearance between 1. Adjust brakes. drums and linings. 2. Automatic adjusters not 2. Make several forward and working. reverse stops; if pedal does not come up, repair automatic adjusters. 3.
  • Page 15 DRUM BRAKE TROUBLESHOOTING SYMPTOM CAUSE REMEDY 6. Scored, hard spotted or out of 6. Refinish or replace drums in round drums. axle sets. 7. Rough or corroded master 7. Refer to vehicle service manual. cylinder bore. 8. Binding brake pedal linkage. 8.
  • Page 16 1. Repair or replace expander unit. not engage. 2. Binding wedge assembly. 2. Repair or replace wedge. 3. Parking brake actuator not 3. Refer to vehicle service manual. working. BW1601 © 2004 Bendix Commercial Vehicle Systems LLC All rights reserved. 6/2004 Printed in U.S.A.

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