Chevrolet 10 1971 Series Chassis Service Manual page 166

BRAKES 5-18
the outlet hole for loose brass burrs, which might have
been turned up when the insert was pressed into position!?
Each vehicle application of these cylinders is designed
to produce the correct displacement of fluid from both
the front and rear chambers under normal, failed and
partially failed conditions. Cylinders are designed so that
this variable displacement requirement is controlled
within each bore size by the secondary piston.
Because the pistons vary in length, it is neccessary to
mark them with identification rings. It is imperative that
exact replacements be made when servicing the master
cylinders. The wrong piston might operate satisfactorily
under normal conditions but fail under conditions of
partial failure.
With all of the variables to be found in master cyl­
inders, which look similar externally, it is important
that the complete assemblies be properly identified. For
this purpose a two-letter metal stamp will be found on the
end of each master cylinder. This two-letter stamp indi­
cates the displacement capabilities of particular master
cylinder. It is, therefore, mandatory that when main
cylinders are replaced, they are replaced with cylinders
bearing the same two-letter stamp.
1. Place new secondary seals in the two grooves in the
flat end of the secondary piston assembly. The seal
which is nearest the flat end will have its lips facing
toward this flat end. The seal in the second groove
should have its lips facing toward the end of the
secondary piston which contains the small compen­
sating holes.
2. Assemble a new primary seal and primary seal
protector over the end of the secondary piston
opposite the secondary seals, so that the flat side
of the seal seats against the flange of the piston
which contains the small compensating holes.
3. In order to insure correct assembly of the primary
piston assembly, a complete primary piston assem-
is included in the repair kits.
4. Coat the bore of the main 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 so that the
retainer locates inside the lips of the primary seal.
5. Holding the main cylinder with the open end of the
bore so that the spring will seat in against the closed
end of the bore. Use a small wooden rod to push
the secondary piston to seat.
6. Place the main 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.
7. Continue to hold the primary piston down. This will
also move the secondary piston forward and will
insure 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 pound inches.
8. Install the reservoir diaphragm in the reservoir
cover and install the cover on the main cylinder.
Assemble the bail wires into position to retain
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
gasket into position.
3. Secure the main cylinder to the firewall with mount-
ting bolts.
This cylinder to dash fastener is an
NOTE:
important attaching part in that it could affect
the performance of vital components and sys­
tems, and/or could result in major repair ex­
pense. It must be replaced with one of the same
part number or with an equivalent part if re­
placement becomes necessary. Do not use a
replacement part of lesser quality or substitute
design. Torque values must be used as specified
during reassembly to assure proper retention
of this part.
4. Connect the push rod clevis to the brake pedal with
pin and retainer.
5. Connect the brake lines to the main cylinder.
6. Fill the main cylinder reservoirs to the levels
shown in Figure 7. Bleed the brake system as
outlined in this section.
7. If necessary, adjust the brake pedal free play as
outlined in this section.
M A IN CYLINDER
(With Frame Mounted Booster) (Fig. 37)
Removal
1. Wipe main cylinder and lines clean with a clean cloth.
Place dry cloths below master cylinder to absorb
any fluid spillage.
2. Disconnect hydraulic lines at main 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, and washers which fasten main
cylinder to dash. Pull main cylinder straight off
push rod and remove from engine compartment.
5. Remove and discard main cylinder push rod boot.
6. Remove main cylinder cover and pour out fluid
from reservoirs. Pump the remaining fluid out by
depressing piston.
Installation
1. Assemble new boot on brake pedal push rod.
2. Place main cylinder in position in engine compart­
ment. Make certain that push rod and boot are in
proper position.
3. Fasten main cylinder to dash with nuts, bolts, and
washers.
4. Connect brake lines to main cylinder.
5. Fill the reservoirs with recommended brake fluid to
level shown in Figure 7.
6. Follow instructions under h e a d i n g of "Bleeding
Brakes".
7. If necessary, adjust the brake pedal free play as
directed.
8. Connect battery ground strap or stop light wires and
brake warning switch wire (whichever was discon­
nected at removal).
10-30 CHEVROLET TRUCK SERVICE MANUAL