Power Unit Service; Power Unit Diagnosis; Power Unit Removal; Power Unit Installation - Jeep 1979 CJ-5 Technical & Service Manual

BRAKES 2G-31
of the power piston to develop atmospheric air pressure
on the power piston.
POWER UNIT SERVICE
All power units are serviced as assemblies only. If
diagnosis indicates that an internal malfunction has
occured within a power unit, replace the unit as an
assembly. Do not attempt to repair the unit.
All power units have a single master cylinder push
rod of a preset, nonadjustable length. When replacing a
power unit, use the push rod supplied with the replace-
ment power unit only. This push rod has been correctly
gauged to the replacement unit.
POWER UNIT DIAGNOSIS
Power unit malfunction should be diagnosed using
Brake Diagnosis Guide B and the Power Unit and Serv-
ice Diagnosis Charts. When diagnosing suspected power
unit malfunctions, always perform the preliminary di-
agnosis procedures outlined in Brake Diagnosis Guide A
first. This is an important step in avoiding inaccurate
diagnosis and ineffective repair.
POWER UNIT REIOVAL
(1) Disconnect power unit push rod at brake pedal.
Discard bolt and nut attaching rod to pedal.
(2) Disconnect vacuum at power unit check valve.
(3) Remove nuts and washers attaching master cyl-
inder to power unit and move master cylinder aside. Do
not disconnect brake lines at master cylinder.
(4) On CJ models, remove nuts and bolts attaching
power unit bellcrank to dash panel and remove power
unit and bellcrank as assembly.
(5) On Cherokee, Wagoneer, and Truck models, re-
move nuts and washers attaching power unit to dash
panel and remove power unit.
N O T E : If the power unit is to be replaced on CJ models,
remove the bellcrank from the original power unit, lub-
ricate the bellcrank pivot pins with chassis lubricant,
and transfer the bellcrank to the replacement unit.
P01ER UNIT INSTALLATION
(1) On Cherokee, Wagoneer and Truck models,
mount power unit on dash panel and install attaching
washers and nuts. Tighten nuts to 35 foot-pounds (47
N*m) torque.
(2) On CJ models, mount assembled power, unit and
bellcrank on dash panel. Install bellcrank-to-dash panel
attaching bolts and nuts. Tighten bolts to 35 foot-pounds
(47 N«m) torque.
(3) Connect vacuum hose to power unit check valve.
(4) Position master cylinder on power unit and in-
stall cylinder attaching washers and nuts. Tighten nuts
to 30 foot-pounds (41 N*m) torque.
(5) Align power unit push rod and brake pedal and
install replacement pedal attaching bolt and nut.
Tighten bolt and nut to 35 foot-pounds (47 N»m) torque.
SPECIFICATIONS
Brake Size and Application Chart
Model
Master Cylinder
Bore Diameter
Front Brakes
Rear Brakes
Power Brake
Unit Type
Model
Master Cylinder
Bore Diameter
Brake Size
And Type
Caliper Piston
Diameter
Brake Size
And Type
Wheel Cyl.
Diameter
Power Brake
Unit Type
CJ
1.00
(25.4 mm)
11.7 Disc.
(29.7 cm)
2.6
Single Piston
(6.60 cm)
10 x 1.75 Drum
(25.4 x 4.44 cm)
.875
(22.2 mm)
8.00
Single Diaphragm
(20.3 cm)
Cherokee
Wagoneer
1.125
(28.5 mm)
12.0 Disc.
(30.48 cm)
2.937
Single Piston
(7.45 cm)
1 1 x 2 D r u m
(27.94 x 5.08 cm)
.937
(23.79 mm)
9 1/2
Single Diaphragm
(24.13 cm)
J-10 Truck
1.125
(28.5 mm)
12.0 Disc.
(30.48 cm)
2.937
Single Piston
(7.45 cm)
1 1 x 2 Drum
(27.94 x 5.08 cm)
.937
(23.79 mm)
9 1/2
Single Diaphragm
(24.13 cm)
J-20 Truck
6800 GVW
1.125
(28.5 mm)
12.5 Disc.
(31.75 cm)
2.937
Single Piston
(7.45 cm)
12 x 2.5 Drum
(30.48 x 6.35 cm)
1.125
(28.5 mm)
9 1/2
Tandem Diaphragm
(24.13 cm)
J-20 Truck
7600 GVW
1.125
(28.5 mm)
12.5 Disc.
(31.75 cm)
2.937
Single Piston
(7.45 cm)
12 x 2.5 Drum
(30.48 x 6.35 cm)
1.125
(28.5 mm)
9 1/2
Tandem Diaphragm
(24.13 cm)
J-20 Truck
8400 GVW
1.125
(28.5 mm)
12.5 Disc.
(31.75 cm)
2.937
Single Piston
(7.45 cm)
12 x 2.5 Drum
(30.48 x 6.35 cm)
1.125
(28.5 mm)
9 1/2
Tandem Diaphragm
(24.13 cm)
4 1 1 0 2