Pontiac tempest 1968 Service Manual page 178

S T A N D A R D BRAKES 5-13
4 . Remove small secondary piston stop bolt from
bottom of front fluid reservoir of master cylinder,
5. Place master cylinder in soft jaws of vise. Re­
move lock ring from small groove In inside diameter
of bore. Remove primary piston (rear). Remove
secondary (front) piston, piston spring and retainer
by applying air pressure through front stop bolt hole.
Do not attempt to disassemble front piston since
complete new assembly is provided in repair kit.
NOTE; If air is not available, a piece of wire may
be used. Bend one fourth inch of one end of wire
into right angle and hook end under edge of floating
piston to remove.
6. For your convenience, in the event they are
needed, repair kits contain replacement check valves
and springs. Following are the conditions under
which the check valves should be replaced:
a. Whenever f l u i d i n b r a k e system i s
contaminated.
b. Whenever foreign material or sediment is
found inside reservoir.
c. If vehicle is 5 years old, or has 10,000 miles
or more on it.
d. If hydraulic brake master cylinder was sub­
jected to excessive heat such as fire due to acci­
dent, etc.
NOTE: In most cases, it will not be necessary to
install new check valves unless conditions above
exist; therefore, unless they do exist, it is not
recommended that the check valves be replaced.
If check valves do require replacement, carefully
follow the service procedure outlined below.
7. With master cylinder in vise (outlet holes up),
drill out the tube fitting insert with a 13/64" drill and
then tap the hole, using a 1/4" x 20 tap. Place a
1/2" to 3/4" long, 1/4" x 20 bolt through a thick
washer and then thread the bolt into the insert.
Tighten the bolt against the washer until the insert
is removed.
8. Remove check valves and springs from cavities
beneath tube seats.
9. Remove master cylinder from vise and inspect
bore for corrosion, pits and foreign matter. Make
sure outlet ports are clean and free of brass cuttings
from tube-seat removal operation. Inspect fluid r e s ­
ervoirs for foreign matter. Check bypass and com­
pensating ports to master cylinder bore to insure
they are not restricted. Do not use wire to check
ports.
10. Remove primary seal, primary seal protector
and secondary seals from front piston.
Cleaning
Use a reputable cleaner or clean brake fluid to
clean all metal brake parts thoroughly. Immerse
parts in cleaning fluid using a bristle brush to r e ­
move foreign matter. Blow out all passages, ori­
fices and valve holes. Air dry and place cleaned
parts on clean paper or lintfree cloth.
NOTE: Dirt is the major cause of trouble and
wear in service. Be sure to keep parts clean until
reassembly. Rewash at reassembly if there is any
occasion to doubt cleanliness.
ASSEMBLE
1. Place master cylinder in vise, with outlet holes
up. Place check valve springs in outlet holes, so
they will seat in depression in bottom of holes.
Place new rubber check valves over springs, being
careful not to displace springs from their seat.
2. Place new brass tube seat in outlet holes in
position to be pressed into outlet hole. Be sure that
it is not cocked, as this would cause burrs to be
turned up when the tube seat is pressed in. Recom­
mended method of inserting tube seat is to thread a
spare brake line tube nut into outlet hole and turn nut
down until tube seat bottoms. (Remove tube nut and
check outlet hole for loose burrs, which might have
been turned up when the tube seat was pressed down.)
3. Put new secondary seals in the two grooves in
the end of front piston. Seal which is nearest the end
of the piston will have its lips facing toward that end.
The second groove seal should have its lips facing
toward the portion of front piston which contains
small compensating holes.
4. Assemble a new primary seal and protector
over end of front piston with flat side of seal seating
against seal protector and protector against flange of
piston which contains the small compensating holes
(Fig. 5-6).
5. All master cylinder overhaul kits contain as­
sembled primary piston, making it unnecessary to
assemble any primary piston component parts.
6. Coat bore of master cylinder, primary and
secondary seals on front piston with clean brake
fluid. Insert secondary piston spring retainer into
secondary piston spring. Place retainer and spring
down over end of front piston locating retainer inside
lips of primary cup.
7. Holding master cylinder with open end of bore
down, push front piston into bore, seating spring
against closed end of bore.
8. Place master cylinder in vise with open end of
bore up. Coat primary and secondary seal on rear
piston with clean brake fluid. Push rear piston as-