
416 LIGHT AND HEAVY VEHICLE TECHNOLOGY
to effect the necessary repositioning of the shoe with
lining wear and also allow a normal running clearance
(Figure 25.14b).
Ratchet-and-pawl and jacking-screw automatic ad-
justers tend to be more elaborate in their application.
With the former arrangement the toothed end of a
ratchet strut may engage a spring-loaded pawl secured
to the brake back plate, while the other end of the strut
is pin jointed with a clearance hole to the brake shoe
(Figure 25.14c). The clearance hole allows the normal
running clearance of the brake shoe with the drum, but
as the lining wears and the shoe moves further outward ...