Chevrolet 10 Series 1968, Service Manual

Page: 252 / 713

BRAKES 5-19
over the springs, being careful not to displace the
springs from the spring seats.
2. Place new brass tube seats in the outlet holes. Be
sure seats are not cocked as this would cause burrs
to be turned up as the tube seats are pressed in.
Thread a spare brake line tube nut into the outlet
hole and turn the nut down until the tube seat
bottoms. Remove the tube nut and check the outlet
hole for loose burrs, which might have been turned
up when the tube seat was pressed down. Repeat this
process to bottom the second seat.
3. Put new secondary seals in the two grooves in the
end of the secondary piston assembly. The seal
which is nearest the end will have its lips facing to­
ward that end. The seal in the second groove should
have its lips facing toward the portion of the second­
ary piston which contains the small compensating
holes.
4. Assemble a new primary seal protector and primary
seal over the end of the secondary piston with the
flat side of the seal seats against the seal protector,
and the protector against the flange of the piston
which contains the small compensating holes.
5. Assemble the new secondary seal into the groove on
the push rod end of the primary piston. The lips of
this seal should face toward the small compensating
holes in the opposite end of the primary piston.
6. Assemble the new primary seal protector and p ri­
mary seal on the end of the primary piston with the
flat side of the seal seated against the seal protector,
and the protector against the flange on the piston
which contains the compensating holes.
7. Assemble the spring retainer in one end of the p ri­
mary piston spring and the secondary piston stop in
the other end. Place the end of the spring over the
end of the primary piston with the spring retainer
seats inside of the lips of the primary seal.
8. Remove all cleaning liquid from the threaded hole in
the primary piston. Place the piston extension screw
down through the secondary piston stop and the p ri­
mary spring retainer and screw it into the primary
piston until it bottoms out.
9. Coat the bore of the master cylinder with clean brake
fluid. Coat the primary and secondary seals on the
secondary piston with clean brake fluid. Insert the
secondary piston spring retainer into the secondary
piston spring. Place the retainer and spring down
over the end of the secondary piston until the re­
tainer locates inside of the lips of the primary cup.
10. Hold the master cylinder with the open end of the
bore down. Push the secondary piston into the bore
until the spring seats against the closed end of the
bore.
11. Position the master cylinder in a vise with the open
end of the bore up. Coat the primary and secondary
seal on the primary piston with clean brake fluid.
Push the primary piston assembly, spring end first,
into the bore of the master cylinder. Hold the piston
down and snap the lock ring into position in the small
groove in the I.D. of the bore.
12. Push the primary piston down to move the secondary
piston forward far enough to clear the stop screw
hole in the bottom of the front fluid reservoir. Install
the stop screw.
13. Install reservoir diaphragm in the reservoir cover
and install the cover on the main cylinder. Push bail
wire into position to secure the reservoir cover.
Installation
1. Assemble the push rod through the push rod retainer,
if it has been disassembled.
2. Push the retainer over the end of the main cylinder.
Assemble new boot over push rod and press it down
over the push rod retainer. Slide new mounting gas­
ket into position.
3. Secure the main cylinder to the firewall or frame
rail as applicable, with mounting bolts.
4. Connect the push rod clevis to the brake pedal with
pin and retainer.
5. Connect the brake lines to the main cylinder.
6. F ill the main cylinder reservoirs to the levels shown
in Figure 15. Bleed the brake system as outlined in
this section (fig. 12).
7. If necessary, adjust the brake pedal free play as out­
lined in this section.
MAIN CYLINDER-SINGLE RESERVOIR TYPE
NOTE:
These main cylinders are of the basic
single hydraulic reservoir type. Cylinders in­
stalled on PA-TA40, and TA50-60 models have
two pistons in the body casting, side by side.
One piston provides regular braking action and
the other provides a hydraulic assist for clutch
operation.
Removal (Fig. 1)
Dual Cylinder (except tilt cab)
1. Disconnect clutch and brake pedal return springs.
2. Detach push rod boots from cylinder tubes.
3. Remove clutch and brake cylinder lines from main
cylinder.
4. Remove the three bolts retaining cylinder assembly
to the front of dash.
5. Remove cylinder assembly from vehicle.
6. Remove cover and dump fluid out of cylinder.
Tilt Cab
1. Tilt cab forward and block in place.
2. Disconnect brake and clutch lines at cylinder and slip
rubber dust boots off cylinder tubes.
3. Remove 3 cylinder attaching bolts and remove cyl­
inder (allowing brake and clutch pedal push rods to
fall loose).
4. Repair the dual brake and clutch cylinder as re ­
quired. See disassembly, inspection and assembly
procedures.
Single Cylinder
1. Disconnect brake pedal return spring.
2. Disconnect the brake hydraulic line at the main cyl­
inder mounted on the cab. Also disconnect lines at
the dash and toe pan.
3. R e m o v e cylinder retaining bolts and remove
cylinder.
4. Remove cover from top of cylinder and dump out
fluid.
Disassem bly (Fig. 33)
Dual Cylinder
Brake cylinder side
1. Remove piston stop snap ring.
CHEVROLET TRUCK SERVICE MANUA
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