Chevrolet Light Duty Truck 1973, Service Manual

Page: 304 / 979

5 - 3 8 BRAKES
bore so that the spring will seat in against the
closed end of the bore. Using a small wooden rod to
push the secondary piston to seat.
6
. Place the master cylinder in a vise with the open
end of the bore up. Coat the primary and
secondary seals on the primary piston with clean
brake fluid. Push the primary piston, secondary
piston stop 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.
CAUTION:
Do not tighten vise too tightly as
damage to the master cylinder could result.
7. Continue to hold the primary piston down. This will
also move the secondary piston forward and will
ensure that the secondary piston will be forward far
enough to clear the stop screw hole, which is in the
bottom of the front fluid reservoir. The stop screw
is now positioned in its hole and tightened to a
torque of 25-40 inch pounds.
CAUTION:
See "Caution" on Page I of this
section.
8
. Install the reservoir diaphragm in the reservoir
cover and install the cover on the master cylinder.
Assemble the bail wire(s) into position to retain the
reservoir cover. The master cylinder is now ready
for "Bench Bleeding".
MASTER CYLINDER - (With Frame
Mounted Booster)
Removal (Fig. 71)
1. Wipe master cylinder and lines clean with a clean
cloth. Place dry cloths below master cylinder to
absorb any fluid spillage.
2. Disconnect hydraulic lines at master cylinder. Cover
line ends with clean, lint-free material to prevent
foreign matter from entering system.
3. Disconnect battery ground strap or stop light wires
and brake warning switch wire.
4. Remove nuts, bolts, washers which fasten master
cylinder to dash. Pull master cylinder straight off
push rod and remove from engine compartment.
5. Remove and discard master cylinder push rod boot.
6
. Remove master cylinder cover and pour out fluid
from reservoir. Pump the remaining fluid out by
depressing piston.
Disassembly
1. Remove cylinder cover bolt and gasket.
2. Lift off reservoir cover and cover seal. Pour out any
excess fluid and stroke piston to force fluid through
outlet ports.
3. Remove piston stop bolt and gasket from bottom of
reservoir housing.
4. Use snap ring pliers and remove retainer ring from
groove in end of cylinder bore.
5. Remove stop plate.
6
. All internal parts should slide easily out of cylinder
bore. If they do not, apply compressed air carefully
at front outlet port. If parts do not remove easily,
examine bore carefully for extensive damage which
may eliminate the possibility of reconditioning the
master cylinder.
Cleaning and Inspection
Clean all parts in clean brake fluid. Inspect cylinder bore
for scratches or corrosion. Minor blemishes can be
removed with crocus cloth or a clean-up hone.
Check by-pass ports in both reservoirs to make sure they
are open and free of burrs.
Remove and discard all rubber parts. All rubber parts
are included in each repair kit.
Assembly
1. Coat all parts with a liberal amount of clean brake
fluid.
2. Install rubber seal cup on secondary piston with cup
lip facing rear (open end of cylinder).
NOTE: All other cup lips face in the opposite
direction (closed end of cylinder.)
3. Stack and install secondary piston spring, pressure
cup and piston in cylinder bore.
4. Install piston stop bolt and gasket, making sure
screw enters cylinder bore behind rear of piston.
5. Assemble and install primary piston parts in
cylinder bore.
6
. Install stop plate in cylinder bore.
7. Compress all parts in cylinder bore and install
retainer ring in groove.
8
. Install reservoir cover and seal.
Installation
1. Assemble new boot on brake pedal push rod.
2. Place master cylinder in position in engine
compartment. Make certain that push rod and boot
are in proper position.
3. Fasten master cylinder to dash with nuts, bolts, and
washers.
CAUTION:
See " Caution
"
on Page 1 of this
section.
4. Connect brake lines to master cylinder.
CAUTIO N:
See
"
Caution
"
on Page 1 of this
section.
5. Fill the reservoir with recommended brake fluid to
level shown in Figure 31.
6
. Follow instructions under heading of "Bleeding
Brakes".
LIGHT DUTY TRUCK SERVICE MANUAL