TCM FB-8 Series, Service Manual

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5.1.3 WHEEL BRAKE
The wheel brake is duo-servo type, and is
mounted on each of the both ends of the drive
axle.
The wheel brake is composed of two pairs of
brake shoes, a wheel cylinder and adjuster.
One end of the brake shoe is contacted with
the anchor pin and another end is contacted with
the adjuster. The brake shoes are pushed against
the backing plate through the shoe hold-down
spring and shoe hold-down pin.
The parking brake mechanism and the
automatic clearance adjuster are also built in the
wheel brake.
(1) Wheel brake operation
The wheel cylinder pushes the primary and
secondary shoes against the brake drum with an
equal force. The shoes are kept turning with the
brake drum until the top of the secondary shoe
comes in contact with the anchor pin.
When the secondary shoe comes in contact
with the anchor pin, the friction force is
generated between the brake lining and the
brake drum, and the primary shoe pushes the
secondary shoe with a stronger force than the
operation force of the wheel cylinder. Powerful
braking force is thus achieved. (See Figure 5.4)
In backward travel, the braking force works
in the reverse direction of forward travel. (See
Figure 5.5)
(2) Parking brake
The parking brake unit is built in the wheel
brake, and consists of a lever and strut.
The lever is installed on the primary shoe
side with a pin. Movement of the lever is also
transmitted to the secondary shoe side through
the strut.
Fig. 5.4 Braking Operation in Forward Travel
ANCHOR PIN
ADJUSTER
Rotation direction
of drum
Fig. 5.5 Braking Operation in Backward Travel
Working force
Primary
Secondary
Fig. 5.6 Parking Brake
PIN
LEVER
PRIMARY SHOE
SECONDARY SHOE
STRUT
5. BRAKE SYSTEM