Power Unit Installation; Drum Brakes - Jeep J-10 Series 1982 Technical & Service Manual

2G-30 BRAKES
tacts the raised seat on the power piston. When contact
occurs, vacuum to the chamber space at the right side of
the power piston is shut off.
At vacuum shut off, air under an atmospheric pres
sure of 14.7 psi (101.3 kPa), then flows into the right side
of the chamber through the air filter. Since a vacuum
still exists in the left side of the chamber, the force of air
at atmospheric pressure on the right side of the power
piston forces the piston and master cylinder push rod to
the left applying the brakes.
When the brake pedal is released, the control valve
returns to its seat against the air inlet valve shutting off
the supply of air under atmospheric pressure. At this
point, engine vacuum coming through the vacuum check
valve again enters the right side of the chamber past the
power piston.
In operation, the single and tandem diaphragm units
function in exactly the same manner with one exception.
The tandem unit utilizes two chambers on the right side
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 Ser
vice Diagnosis Charts. When diagnosing suspected
power unit malfunctions, always perform the prelimi
nary diagnosis procedures outlined in Brake Diagnosis
Guide A first. This is an important step in avoiding
inaccurate diagnosis and ineffective repair.
POWER UNIT REMOVAL
(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 and Scrambler 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.
NOTE: If the power unit is to be replaced on CJ and
Scrambler models, remove the bellcrank from the origi
nal power unit, lubricate the bellcrank pivot pins with
chassis lubricant, and transfer the bellcrank to the re
placement unit.
POWER 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 and Scrambler models, mount assembled
power unit and bellcrank on dash panel. Install bell-
crank-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.
DRUM BRAKES
Page
Brakedrum Service 26-35
Brake Service—Cherokee-Wagoneer-Truck Models 26-34
Brake Service—CJ-Scrambler Models 26-32
GENERAL
Two different drum brake units are used on Jeep
vehicles. The brakes used on CJ and Scrambler models
have a cable operated automatic adjuster mechanism,
while the brakes used on Cherokee, Wagoneer and Truck
models have a linkage operated automatic adjuster
Pago
General 26-30
Operation end Wear Compensation 26-31
Specifications 26-36
mechanism. Although the units differ slightly in con
struction, operation and service procedures for both
units are similar.
Each drum brake unit consists of a support plate, a
primary and a secondary brakeshoe, two brakeshoe re
turn springs, an adjusting screw assembly, two hold-
down springs, automatic adjuster components, and a
wheel cylinder assembly (figs. 2G-25 and 2G-26).