Chevrolet 70 1969 Series, Shop Manual

Page: 253 / 913

BRAKES 5B-60
Inlet Port ^
I
(Service Brakes) Inlet Port
(Parking Brake!
1 Spring Lock 12 Wedge Rod (Part of
2 Release Bolt Wedge Assembly
3 Spring and Cap 13 Non-Pressure
Assembly Housing
4 Release Bolt Nut
14 O-Ring
5 Piston
15 Rubber Washer
6 Pressure Housing 16 Spring
7 Clamping Ring 17 Rivet
8 Rubber Diaphragm 18 Retainer Plate
9 Diaphragm Plate 19 Piston Seal
Rod
20 Expander
10 Rubber Boot 21 Spring Lock
11 Wedge Rod Guide Capscrew
T -2199
Figure 36— “Fail-Safe" Brake Chamber Assembly
brake will remain inoperative until the spring re­
lease bolts are backed out (counterclockwise) as
far as possible to release the springs. Push park­
ing brake valve knob in to released position to
admit air pressure into the parking brake chambers
to hold springs compressed while turning the re­
lease bolts.
C A U T IO N : Under no circumstances should
any service operations be attempted on the brake
chambers without first compressing the springs
by means of the release bolts. Applying air pres­
sure (at least 60 psi) to the parking brake cham ­
bers, either from the vehicle air system or from
shop air supply, will hold springs compressed and
facilitate turning bolts.
M E C H A N IC A L A C T U A T IN G C O M P O N E N T S
(Refer to Fig. 29)
When pressure is applied to the brake cham ­
ber diaphragm plate rod, either by air pressure
during a service brake application or by spring
pressure from the parking brake chamber, move­
ment is transmitted to both ends of each brake
shoe through wedges, rollers, and plungers which
are installed in the actuating housing in the brake
spider. One plunger for each shoe incorporates an
adjusting wheel to provide a means of adjusting
the brakes to compensate for normal lining wear.
All Stopmaster brakes have automatic adjuster
mechanisms.
SERVICEABILITY TESTS
O P E R A T IN G T E S T
1. Service Brakes
Make a brake application and check expansion
of brake shoes against drum. Shoes should move
freely and instantly when brake treadle is depress­
ed. Release treadle. Shoes should contract and
release brakes without any lag. Visually inspect
entire lining area to see if lining is bearing prop­
erly on both sides.
2. Parking Brakes
Apply parking brakes by pulling knob of con­
trol valve to release air from chamber. Brakes
should apply promptly and should hold on any grade
on which vehicle is expected to operate. Release
the brakes by pushing knob in. Brakes should re­
lease instantly and wheels turn freely.
L E A K A G E T E S T
1. Service Brakes
With brakes applied, check air chambers for
leakage at clamping ring by covering ring with
soap suds. Also apply suds to drain holes on bot­
tom of chamber. Any small air leaks should be
evident. No leakage is permissible at either loca­
tion. If leakage occurs at clamping ring, tighten
clamping ring. If leakage persists, diaphragm may
be damaged or not fitting properly between pres­
sure and non-pressure housings (see figs. 36 and 37).
If air is escaping from drain holes only, it is
an indication that diaphragm is faulty.
2. Parking Brakes
a. With parking brake released by air pres­
sure, apply soap suds on cap around release bolt.
Any leakage that is evident indicates a faulty piston
seal. Seal should be replaced and suds applied
again to be sure leakage has been corrected.
b. Soap suds should be applied at cap to pres­
sure housing joint. If leakage is evident, fault
could be due to distorted cap caused by careless
handling or deteriorated rubber washer between
cap and housing.
c. Coat service brake relay valve exhaust
port with soap suds. Leakage at this point indicates
leakage past O-ring seal in the pressure housing.
If leakage occurs, replace O-ring with new part.
CHEVROLET SERIES 70-80 H EAVY DUTY TRUCK SH O P M A N U A L