Power Brake Assembly - Pontiac Grand Prix Service Manual

5B-6 1969
PONTIAC SERVICE MANUAL
Remove power brake assembly from vise and remove
tool J 22805-0 1.
NOTE: Befoe reassembling master cylinder to power
section, the distance fmm the outer end of the push rod
to the master cylinder must be measured as explained
under PUSH ROD ADJUSTMENT below.
PUSH ROD ADJUSTMENT
The push rod is designed with a self-locking adjust-
ment screw to provide the correct relationship between
the vacuum power piston and master cylinder piston.
The adjustment screw is set to the correct height at the
time of original assembly of the power unit. Under
normal service conditions the adjustment screw does
not require any further attention 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
adjustment screw to the mounting face of the power
cylinder should be rechecked either with a micrometer
depth gage to a dimension of 1.225 to 1.210" or with
height gage J 22644. Place gage over the push rod on
the front housing. Cutout portion of the gage 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 BE
PULLED OUT OF DIAPHRAGM PLATE AND
FALL INTO FRONT VACUUM CHAMBER.) Use a
5/16" wrench to turn adjusting nut "in" to shorten, or
"out" to lengthen push rod.
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 reservoirs, and then stroking the power unit.
If fluid spurts, the compensating ports are clear. If the
primary- cups overlap the compensating ports, there
will be no flow of air or fluid through the compensat-
ing 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 pressure
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.
POWER BRAKE ASSEMBLY
-
INSTALL,
1. Place power brake into position and install four rear
housing to dash attaching nuts fmm inside of car.
Tighten nuts to 24 lb. ft. torque.
2. Install clevis pin retainer.
3. Adjust stop light switch if necessary. See section 5
for senice.
4. Attach vacuum hose to vacuum check valve.
5. Attach master cylinder to power section. Torque
nuts to 25 lb. ft.
6. Bleed brakes as necessary and fill fluid reservoirs.
Fluid level should be as shown in Section 5.
TORQUE SPECIFICATIONS
Piston Stop Screw..
.......................
.40 Ib. in.
Power Cylinder Housing to
Master Cylinder Nuts.
..................
-25 lb. ft.
Rear Housing to Dash Nuts.
................
.24
lb. ft.