MOTOR TRUCK SERVICE MANUAL
BRAKES-AIRI
POWER UNIT ADJUSTMENT
The air chamber should be screwed into the wedge bore of the plunger housing to a depth such that the wedge is ready to
lift the plungers off of the abutment seats at the first
movement of the diaphragm (or piston). This provides the
least lost motion and maximum useful chamber (or piston)
stroke. Current power units are designed to "bottom out" in
the wedge bore and provide this optimum adjustment
automatically. (The bottoming type units have a short
unthreaded portion on the leading end.) manually
The newer bottoming type units can be used as
replacements for the earlier units to obtain the bottoming
feature.
WEDGE ALIGNMENT
Whenever the power unit is removed from the brake, the
wedge assembly may also become dislodged. Before
reinstalling the power unit, reposition the wedge assembly
so that the rollers and roller cage are engaged in the
plunger slots.
On newer brake assemblies this is
accomplished automatically by simply aligning the two ears
on wedge spring retainer with corresponding grooves in
the wedge bore of the plunger housing.
On older
assemblies, the wedge head must be aligned manually so
that the rollers engage the plunger slots properly. In either
case, proper alignment can be checked by pushing on the
wedge rod while visually checking for shoe and plunger lift.
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