Pontiac tempest 1968 Service Manual page 201

5B-6
1968 P O N T I A C SERVICE MANUAL
4. Place master cylinder or Tool J-22805-01 in
vise with front housing up.
5. Place diaphragm return spring In front housing,
small end down.
6. Apply silicone grease or talcum powder to all
surfaces of outer bead of diaphragm that bear against
front and rear housings.
7. Place rear housing assembly over diaphragm
return spring and, using tool J 9504 press down
firmly on rear housing, guiding push rod into front
housing seal making certain scribe marks will align
when housings are locked together. Rotate tool
counter-clockwise to lock the two housings. Vacuum
may be applied to the check valve to help draw the
housings together.
CAUTION: Do not release pressure on rear hous­
ing until the housings are fully locked.
NOTE; Be sure diaphragm is not pinched during
assembly.
ASSEMBLE MASTER CYLINDER TO POWER UNIT
Remove master cylinder and power brake assem­
bly from vise and remove old master cylinder
assembly or Tool J-22805-01.
NOTE; Before reassembling master cylinder to
power section, the distance from the outer end of
the push rod to the master cylinder must be
measured as explained under PUSH ROD ADJUST­
MENT below.
PUSH ROD ADJUSTMENT
The push rod is designed with a self-locking ad­
justment screw to provide the correct relationship
between the vacuum power piston and master cylin­
der piston. The adjustment screw is set to the cor­
rect height at the time of original assembly of the
power unit. Under normal service conditions the
adjustment screw does not require any further at­
tention providing the push rod assembly remains in
the original unit.
Whether a new push rod is used or the push rod
assembly is transferred to a unit other than the
original one, the distance from the end of the adjust­
ment screw to the mounting face of the power cylin­
der should be rechecked either with a micrometer
depth gauge to a dimension of 1.225 to 1.210" or
with height gauge J 22644. Place gauge over the
push rod on the front housing. Cutout portion of the
gauge should never be lower than the adjustment
screw end of the push rod and the gap between the
cutout and edge of the push rod end should never
exceed .010". (Fig. 5B-7)
To adjust push rod, grip splined area of push rod
with pliers, being careful not to scratch machined
shaft. (DO NOT REMOVE PUSH ROD FROM POWER
CYLINDER SINCE REACTION DISC MIGHT B E
P U L L E D OUT O F DIAPHRAGM P L A T E AND F A L L
INTO FRONT VACUUM CHAMBER.) Use a 5/16"
wrench to turn adjusting nut in to shorten or out
to lengthen push rod.
When push rod adjustment is correct, assemble
master cylinder assembly to the power unit vacuum
cylinder at two studs. Secure with two nuts and lock
washers tightening to 25 lb. ft. torque.
After assembly of the master cylinder to the power
unit, the primary cups of the master cylinder must
clear the compensating hole when the unit is in the
released position. This can be checked by partially
filling the reservoir, and then stroking the power
unit. If air bubbles appear or fluid spurts, the com­
pensating ports are clear. If the primary cups over­
lap the compensating ports, there will be no flow of
air or fluid through the compensating port when
stroked. If this condition exists, the adjusting screw
should be turned into the push rod a slight amount,
or until the compensating port is open. Failure to
clear the compensating port in the released position
traps fluid in the hydraulic lines and wheel cylinders
and causes brake drag when the fluid warms up.
If compensating port is blocked, fluid from pres­
sure bleeder will flow thru bypass main metering
port behind primary cup and then thru holes in
piston, around lip of primary cup to wheel cylinders.
TORQUE SPECIFICATIONS
Piston Stop Screw . . . . . . . . . . . . 40 lb. in.
Power cylinder housing to
master cylinder nuts 25 lb. ft.
Rear housing to dash nuts 25 lb. ft.