Lesson l/Learning Event 1
CONSTRUCTION
FIGURE 9. EXTERNALCONTRACTING BRAKE.
The M151series trucks use an externalcontractingtype brake that is
mounted on the transmission or transfer. It has a brake drum that is
splined and bolted to a transfer output shaft. A flexible brake band
with internal lining is located around the outer circle of the drum.
The brake is made to be selfenergizing by either forward or backward
movement of the vehicle. For this reason, the brake band is anchored
at a point just opposite from the point where the operating force is
applied. Onehalf of the band will then wrap tighter (selfenergize)
on the drum in one direction and the other half in the opposite
direction. The mechanism for operating the brake is usually a simple
bell crank arrangement controlled by a hand lever. Applying the
brake locks the transmission or transfer output shaft, which, in
turn, locks the propeller shaft holding the wheels through the axle
assembly. When the hand lever is in the released position, the brake
band is released by spring pressure.
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