BENDIX SD-20-6608 User Manual
3
FIGURE 7 - ADJUSTER OPERATION
moves forward, the wedge rollers force the expander
abutment tappet and roller tappet/piston apart, Figure 5,
and directly, or through the expander input tappet/piston
the brake shoes are forced against the drum. In parking
brake operation the brake assembly is a one leading and
one trailing shoe brake, in either forward or reverse drum
rotation.
abutment tappet and roller tappet/piston apart, Figure 5,
and directly, or through the expander input tappet/piston
the brake shoes are forced against the drum. In parking
brake operation the brake assembly is a one leading and
one trailing shoe brake, in either forward or reverse drum
rotation.
AUTOMATIC ADJUSTMENT OF BRAKE SHOES
In the A2LS
™
drum brakes, automatic adjustment is
controlled by the wheel cylinder units. Adjuster assemblies
within the wheel cylinder units control the clearance
between the drum and brake shoe by the back-lash built
into each adjuster mechanism. During braking application,
when no adjustment is required, brake shoe travel takes
place within the back-lash available. As the linings wear
and the distance between the lining and drum exceeds
the predetermined clearance, travel of the piston exceeds
the back-lash available and adjustment of the brake shoe
is automatically made. Each wheel cylinder piston has
an adjuster mechanism screwed into it (Figure 6). The
rotation of this adjuster relative to the piston adjusts the
brake shoes according to the amount of lining wear. The
adjuster shaft has a fast helix thread; onto this is mounted
a drive ring having a corresponding thread with an axial
clearance (back-lash) built in.
within the wheel cylinder units control the clearance
between the drum and brake shoe by the back-lash built
into each adjuster mechanism. During braking application,
when no adjustment is required, brake shoe travel takes
place within the back-lash available. As the linings wear
and the distance between the lining and drum exceeds
the predetermined clearance, travel of the piston exceeds
the back-lash available and adjustment of the brake shoe
is automatically made. Each wheel cylinder piston has
an adjuster mechanism screwed into it (Figure 6). The
rotation of this adjuster relative to the piston adjusts the
brake shoes according to the amount of lining wear. The
adjuster shaft has a fast helix thread; onto this is mounted
a drive ring having a corresponding thread with an axial
clearance (back-lash) built in.
DRIVE
RING
DRIVE
RING
ADJUSTER
SCREW
ADJUSTER
SCREW
DRIVE
RING
SEATED
ADJUSTER
SCREW
SEATED
DRIVE
RING
SEATED
SHOE RETURN
SPRING LOAD
PISTON AND ADJUSTER
(SCREW MOVE OUT)
SPRING LOAD
NORMAL APPLICATION
(NO ADJUSTMENT REQUIRED)
AT REST
FIGURE 6 - WHEEL CYLINDER ASSEMBLY CUT-AWAY
MANUAL OVERRIDE
WHEEL
PISTON
SEAL
ADJUSTER
SHAFT HELIX
ADJUSTER
DRIVE RING
DRIVE RING
SPRING
The adjuster drive ring is held in light contact with its seat
in the cylinder body by the drive ring spring. The brake
shoe tip engaging in the piston tappet head, and a spring
between the adjuster shaft assembly and the face of the
adjuster bore, insure that a back-lash is maintained on the
mating threads of the adjuster shaft and piston.
in the cylinder body by the drive ring spring. The brake
shoe tip engaging in the piston tappet head, and a spring
between the adjuster shaft assembly and the face of the
adjuster bore, insure that a back-lash is maintained on the
mating threads of the adjuster shaft and piston.
When the brake pedal is applied, hydraulic fl uid pressure
causes the piston to move outwards, lifting the adjuster
causes the piston to move outwards, lifting the adjuster