Chevrolet Light Duty Truck 1973, Service Manual

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BRAKES 5 -3 7
outlet holes are up. Enlarge the outlet holes in
the tube seats using a 13/64" drill. Tape a 1/4"
- 20 thread in these holes. Place a heavy washer
over the outlet on the master 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
reservoirs for foreign matter. Check the bypass and
compensating ports to the master 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 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. 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 with crocus cloth or fine
emery paper, washing clean afterwards.
CAUTION:
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.
IF there is any suspicion of contamination or
any evidence of corrosion, completely flush the
vehicle hydraulic brake system in accordance
with this shop manual. Failure to clean the
hydraulic brake system can result in early
repetition 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
extensive 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.
Assembly
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 and turn the nuts down until the
insert bottoms.
Remove the tube nut and check 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 necessary to
mark them with identification rings. It is imperative that
exact replacements be made when servicing the master
cylinders.
With all of the variables to be found in master cylinders,
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
indicates the displacement capabilities of that particular
master cylinder. It is, therefore, mandatory that when
master 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 lip facing
toward this flat end. On Delco units, the seal in the
second groove should have its lips facing toward the
end of the secondary piston which contains the
small compensating holes. On Bendix units, the seal
in the second groove is an "O" ring seal.
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 ensure a correct assembly of the
primary piston assembly, a complete primary piston
assembly is included in the repair kits.
4. 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 so
that the retainer locates inside the lips of the
primary seal.
5. Hold the master cylinder with the open end of the
LIGHT DUTY TRUCK SERVICE MANUAL