Chevrolet 70 1969 Series, Shop Manual

Page: 245 / 913

BRAKES S B -52
STOPMASTER
BRAKES
The Stopmaster type brake differs from the
conventional "S ” cam type brake in several re­
spects, The air chamber push rod is connected to
the brake shoes through a series of wedges, roll­
ers, and plungers rather than through a slack ad­
juster and camshaft, Stopmaster brakes are used
at the rear wheels only, Stopmaster brakes employ
two different type air chambers: (1) a standard
air chamber which is operated by air pressure and
(2) a "Fail-Safe" air chamber 'which can be oper­
ated either by air pressure or by spring pressure.
There are three basic variations of Stopmaster
brakes shown in figure 23,
AUTOMATIC
ADJUSTER
All Stopmaster braises have automatic adjust­
er mechanisms. The basic part of the adjuster
(refer to fig. 24) is a plunger assembly which is
made up of the adjusting
, the actuator, and
the adjusting bolt.. The Threaded intern­
ally to receive adjusting b . ’ ' e external sur~
f i g u r e
face, there are buttress type teeth. The plunger
guide is free to slide in a drilled hole in the spider
housing and has teeth to match those on the exter­
ior surface of the actuator. A spring, gasket, and
bolt are used to hold the guide in contact with the
actuator.
Figure 25 is an illustration of an automatic
adjuster assembly installed. When the plunger as­
sembly is moved outward to apply the shoe against
the drum, the plunger guide will slide across the
sloping sides of the teeth on the actuator. If the
plunger assembly moves outward and exceeds the
pitch distance, the teeth on the guide will engage
the next teeth on the actuator. When the plunger
returns, the actuator must rotate in order to allow
the assembly to return to the "in" position. This
rotation is caused by the angle of the teeth. As the
actuator rotates, it screws the adjusting bolt. The
distance for the plunger to move before adjusting
is controlled either by the angle of the teeth, and/
or the number of teeth. This travel establishes
the lining-drum clearance.
The plunger guide has two flat sides, which
are a slip fit in a slot in the adjusting plunger.
This performs two functions: (1) it prevents the
guide from turning, and (2) it prevents the adjust­
ing plunger from, turning in the housing.
In order to function properly the adjusting
bolt must not turn. If it rotates with the actuator,
no adjustment would occur.
The combination of the number of teeth on the
[ the actuator and the number of threads
on the adjusting bolt establishes the ac-
r advance or rate of adjustment.
Kiures covering the removal and install-
ratomatic adjuster components are given
owing paragraphs:
CHEVROLET SERIES 70-80 H EAVY DUTY TRUCK SH O P M A N U A L