Lesson 1/Learning Event 1
The parking brake system of the M880 and M1008series vehicles uses
the rear wheel drum brakes to hold the vehicle motionless. When the
operator of the vehicle applies the parking brake, the effort with
which the brake lever is moved is transmitted to the rear shoes by
cables. Levers in the system multiply the physical effort of the
operator enough to force the rear brake shoes into tight contact with
the drums.
The parking brake system of the M998series vehicles use a disk
mounted on the rear differential propeller shaft to hold the vehicle
motionless. When the operator of the vehicle applies the parking
brake, a mechanical linkage multiplies the force of the operator, and
transmits this increased pressure to the brake unit. The brake unit
uses the force to push the brake pads against the drum.
Some large trucks use a parking brake that has a drum with internal
expanding brake shoes similar to the service brakes. Braking action
is obtained by clamping the rotating drum between two brake shoes.
The lining on the brake shoes contacts the friction surfaces of the
drum.
The 2 1/2 and 5ton military trucks have a parking brake that
operates by clamping the flange of a drum between brake shoes.
Although it is constructed somewhat different, it uses the same
operating principles as the disk brake. The brake is mounted on the
rear of the transfer and locks the wheels through the axle assemblies
and propeller shafts. The drum has a flange with both inner and
outer braking surfaces. Brake shoes with linings are located on the
inside as well as the outside of the drum. The outer brake shoe is
supported by the pivots on an anchor at its lower end. The inner
brake shoe is supported by the brake shoe lever, which is pinned to
the center of both the outer and inner brake shoes. Pulling the
brake shoe lever moves the brake shoes together clamping the drum
flange between them.
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