SELF-ADJUSTING DEVICE FOR TAKING UP PLAY BETWEEN
SHOES AND DRUM
The self-adjustment device ensures
clearance between shoe and drum is taken up automatically upon each
braking manoeuvre, provided adjustment is required at that time. The device consists of a link (1) within
which adjustment screw (2), to which is bolted toothed wheel (3),
is free to slide. In rest position, front spring (6) recalls
the shoe and maintains the device under compression. Wheel (3) therefore
presses plate (4) into contact with the end of the link (1). Plate (4) is also subject to a pressing
action by means of flexible blade (5). During the braking action,
both brake shoes move apart and come into contact with the drum;
both ends of the device are held in contact with the shoes by
means of springs (7) and (8). Plate (4) is pressed by flexible blade (5)
where it acts against toothed wheel (3). Retainer holds it in permanent
contact with the toothed wheel, which it causes to rotate.
SELF-ADJUSTING DEVICE FOR TAKING UP PLAY BETWEEN
SHOES AND DRUM
During the release stage, the
self-adjustment device is again compressed through the action of
the upper shoe return spring. Toothed wheel (1) stops in the angular
position assumed during braking. The wheel stops during the rotation stage
due to friction between plate (2) and toothed wheel (1). With toothed
wheel (1) locked during the rotation stage, if the linings are sufficiently
worn due to previous braking manoeuvres, retainer (3) moves on and
engages the next tooth.
SELF-ADJUSTING DEVICE FOR TAKING UP PLAY BETWEEN
SHOES AND DRUM
The maximum travel of toothed
wheel (1) on adjustment screw (2) is one tooth (0.020 - 0.025 m);
one exception to this is brakes bedding following dismantling:
travel is two teeth. If the brakes should overheat to 100° ÷ 110°C
as a result of excess braking, the flexible blade (3) comes into
operation by bending and locking plate (4) in neutral position.
SELF-ADJUSTING DEVICE FOR TAKING UP PLAY BETWEEN
SHOES AND DRUM
During braking, the toothed wheel
is no longer subject to the thrusting action of the flexible blade.
The retainer therefore assumes the same angle as the wheel tooth,
which is free to slide on the retainer with the adjustment screw
without taking up clearance due to drum expansion. During service, before fitting the brake
linings, move the device toothed wheel into contact with the spring
and unscrew by half a turn.
