Main Cylinder Component Replacement; Rubber Parts - Chevrolet 10 1971 Series Chassis Service Manual

could result in major repair expense. It must be
replaced with one of the same part number or with
an equivalent part if replacement becomes neces­
sary. 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.
3. Connect the push rod clevis to the brake pedal with
pin and retainer.
4. Connect the brake lines to the main cylinder.
5. Fill the main cylinder reservoirs to the levels
shown in Figure 7.
outlined in this section.
6. If necessary, adjust the brake pedal free play as
outlined in this section.
M ain Cylinder Component Replacement (Fig. 36)
1. Remove the small secondary piston stop screw from
the bottom of the front fluid reservoir of the master
cylinder.
2. Place the main cylinder in the vise so that the lock
ring can be removed from the small groove in the
I.D. of the bore. Remove the lock ring and primary
piston assembly. Remove the secondary piston, sec­
ondary piston spring and retainer by blowing air
through the stop screw hole. If air is not available,
a piece of wire may be used. Bend approximately
1/4" of one end of the wire into a right angle. Hook
this end under the edge of the secondary piston and
pull the secondary piston from the bore.
The brass tube-fitting insert should not
NOTE:
be removed unless visual inspection indicates
the insert is damaged.
3. To replace a defective insert the following procedure
should be practiced:
a. Place the main cylinder in a vise, so that the
outlet holes are up. Enlarge the outlet holes
in the tube seats using a 13/64'' drill. Tap a
1/4" - 20 thread in these holes. Place a heavy
washer over the outlet on the main cylinder and
thread a 1/4" - 20 x 3/4" hex head bolt into the
tube seat. Tighten the bolt until the tube seat is
unseated.
b. A more preferable way to remove a defective
insert involves use of a self-tapping screw and a
claw hammer. With a box-end or socket wrench,
thread a #6 - 32 x 5/8" long self-tapping screw
into the tube-fitting insert. Using the claw end of
the hammer, remove the screw and insert.
4. Remove the casting from the vise and inspect the
bore for corrosion, pits and foreign matter. Be sure
the outlet ports are clean. Inspect the fluid reser­
voirs for foreign matter. Check the bypass and
compensating ports to the main cylinder bore to
determine if they are unrestricted.
5. Remove the primary seal, primary seal protector
and secondary seals from the secondary piston.
Cleaning
Use denatured alcohol or clean brake fluid to thoroughly
clean all reusable brake parts. Immerse in the cleaning
fluid and brush metal parts with hair brush to remove
foreign matter. Blow out all passages, orifices and valve
holes. Air dry and place cleaned parts on clean paper or
lintfree clean cloth. If slight rust is found inside either
the front or rear half housing assemblies, polish clean
Bleed the brake system as
Fig. 36— M ain Cylinder - Explode
with crocus cloth or fine emery paper, washing clean
afterwards.
Dirt is the major cause of trouble and
NOTE:
wear in service. Be sure to keep parts clean
until re-assembly. Re-wash at re-assembly if
there is any occasion to doubt cleanliness - such
as parts dropped or left exposed for eight hours
or longer.
Reassembly
If there is any suspicion of contami­
CAUTION:
nation or any evidence of corrosion, completely
flush the car hydraulic brake system in accord­
ance with the vehicle shop manual. Failure to
clean the hydraulic brake system can result
in early repitition of trouble. Use of gasoline,
kerosene, anti-freeze, alcohol or any other
cleaner, with even a trace of mineral oil, will
damage rubber parts.

Rubber Parts

Wipe fluid from the rubber parts and carefully inspect
each rubber part for cuts, nicks or other damage. These
parts are the key to the control of fluid flow. If the unit
is in for overhaul, or if there is any question as to the
serviceability of rubber parts, REPLACE them!
Badly damaged items, or those which would take exten­
sive work or time to repair, should be replaced. In case
of doubt, install new parts. Do not rely on the brake unit
being overhauled at an early or proper interval. New
parts will provide more satisfactory service, even if the
brake unit is allowed to go beyond the desired overhaul
period.
Main Cylinder
If the brass tube inserts were removed, place the
master cylinder in a vise so that the outlet holes are up.
Position the new brass tube inserts in the outlet holes,
making sure they are not cocked. The recommended
method of seating these inserts is to thread a spare brake
line tube nut into each outlet hole and turn the nuts down
until the insert bottoms. (Remove the tube nut and check
BRAKES 5-17
10-30 CHEVROLET TRUCK SERVICE MANUAL