AUTOMATIC SLACK ADJUSTER MAINTENANCE
a. The Automatic Slack Adjusters incorporate a series of worm gears, load sensing springs and clutches
housed in an environmentally sealed body. The control arm is secured to the axle assembly by means of an
b. During brake application and when the shoes contact the drum, torque is generated at the foundation
brake which overcomes the internal spring load. This allows a worm shaft to disengage from the adjusting
mechanism, resulting in the adjusting clutches being isolated and protected from the high torques and stress
developed during brake application.
c. During brake release, the rack begins to rotate the one-way clutch gear in a driving direction. Since the
worm shaft is still disconnected from the clutch mechanism, no adjustment is made. As the brake shoes leave
the drum, the torque from the foundation brake is reduced allowing spring force to reconnect the worm shaft
and adjusting clutches. At this point, the rack stops driving the one-way clutch and passes through a
clearance notch which results in a "No Adjust" signal to the clutches. This "No Adjust" portion of the return
travel is the point at which the predetermined running clearance is installed. After the rack passes through
the clearance notch, and additional return travel is required for complete brake release, the rack again rotates
the one-way clutch gear in the driving direction (worm shaft now reconnected) which rotates the worm shaft
resulting in an adjustment at the brake shoe.
d. This process is repeated on every brake apply and release. The greater the amount of return travel (after
the clearance notch is passed through) the greater the amount of adjustment. On each subsequent brake apply
and release, the amount of adjustment becomes smaller until the excess clearance is removed. When the
adjuster reaches the full release position at the same time the rack passes through the clearance notch, the
predetermined shoe-to-drum clearance is reached and no additional adjustment is required.