Pontiac FIREBIRD 1972 Service Manual page 426

Fig. 5-20 Master Cylinder
-
Exploded View
MASTER CYLINDER
REMOVE
1. Disconnect master cylinder push rod from brake
pedal.
2. Disconnect brake lines from two outlets on master
cylinder and cover end of lines and outlet ports to
prevent entrance of dirt.
3. Remove master cylinder from dash.
DISASSEMBLE
1. Remove master cylinder reservoir cover and drain
fluid. Pump fluid from master cylinder by depressing
push rod.
2. A retained push rod is used on all standard brake
applications. Pull back boot to uncover push rod re-
tainer. The retainer has a small, depressed tab in the
side which may be pried up to release retainer. Tab
serves to hold retainer and push rod on master cylin-
der while it is being shipped and it is not necessary
to bend tab down at reassembly. Retainer is held in
place between master cylinder and dash when master
cylinder is bolted in place.
3. Remove small secondary piston stop bolt from bot-
tom of front fluid reservoir of master cylinder.
4. Place master cylinder in soft jaws of vise. Remove
lock ring from small groove in inside diameter of
bore. Remove primary piston (rear). Remove second-
ary (front) piston, piston spring and retainer by ap-
plying air pressure through front piston stop bolt
hole. Do not attempt to disassemble rear 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.
5. 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.
6. 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 reservoirs
for foreign matter. Check bypass and compensating
ports to master cylinder bore to insure they are not
restricted.
7. Remove primary seal, primary seal protector and sec-
ondary seals from front piston.
CLEANING
CAUTION: Honing of master cylinders is not
recommended as it creates a finish which is
much rougher than original. It is best to replace
a corroded master cylinder. Discolored or
stained areas may be polished with crocus
cloth. Use a circular motion. Do not slide the
cloth in a length wise direction under pressure.
Do not use any other form ofabrasive or abra-
sive cloth.
Use alcohol or clean brake fluid to clean all metal brake
parts thoroughly. Immerse parts in cleaning fluid using a
bristle brush to remove foreign matter. Blow out all pas-
sages, orifices and valve holes. Air dry and place cleaned
parts on clean paper or lint free 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 (FIG. 5-2 AND 5-20)
1. Place master cylinder in vise, with outlet holes up.
2. Place new brass tube seat in outlet holes. Be sure that
it is not cocked, as this would cause burrs. 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 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