Automatic slack adjuster
Start Position Pre-Set Running Clearance
In the start position the toe of the rack touches the top of the cut-out. On the forward stroke the ASA rotates. The rotation of the ASA means the toe of the rack changes position and now touches the bottom of the cut-out.
Excess Clearance Phase
If there is Excess Clearance or wear, the stroke will be longer and the ASA will rotate further. The rack will remain touching the bottom of the cut-out throughout the forward stroke, therefore rotating the pinion in the slip direction of the one-way clutch assembly.
When the brake linings touch the brake drum the ASA continues to rotate due to Elasticity in the brake. The increasing camshaft torque acts through the worm wheel and worm shaft, the coil spring is compressed and the conical clutch disengages.
On the return stroke the ASA starts to rotate in the opposite direction. The rack is held down, keeping the same position in the cut-out, and rotates the one way clutch assembly, still disengaged from the worm shaft, in the opposite direction.
Pre-Set Running Clearance Phase
The rack moves with the housing during this phase, therefore the rack does not rotate the pinion. As the ASA rotates through the return stroke, the toe of the rack will move from the bottom to the top of the cut-out.
The ASA continues to rotate through the return stroke. Held by the cut-out, the rack drives the one-way clutch assembly. The conical clutch is engaged, so the worm shaft rotates and indexes the worm wheel within the housing.
Installation instructions are common to ASA type and S-ABA type Automatic Slack Adjusters.
Do not use air wrenches or hammers. Their use will damage the product, prevent correct function and will void the warranty.
Make sure that the brake chamber push rod is fully released. A minimum pressure of 6 bar is required. Clean the camshaft spline.
Now,fit the wear indicator and return spring (if needed),and secure the slack adjuster on the camshaft.
Grease the camshaft spline. Fit the new slotted anchor bracket but do not tighten it.
Following the direction of the arrow on the slack adjuster body, rotate the control arm as far as possible. Do not hammer the control arm. Fix the anchor bracket by tightening the mounting bolts.
Fit the slack adjuster onto the camshaft. Pay attention to the arrow in the housing.
Rotate the hexagon nut clockwise until the brake lining touches the brake drum. Do not use an air wrench.
Match the hole in the slack adjuster with the holes in the clevis, by rotating the hexagon nut clockwise. Do not use an air wrench to do this.
Turn the hexagon nut at a 3/4 turn anti-clockwise to adjust the brake clearance. It should produce a loud noise. Do not use an air wrench.
Grease the clevis pin and then fit and secure it. It should be able to rotate freely.
Leave a ring spanner on the hexagon nut and apply the brakes 5 times. If the hexagon nut rotates clockwise, the slack adjuster is working correctly.
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