JEEP CHEROKEE 1988 Service Repair Manual

GEA R T O OTH C O NTA C T P A TTE R NS

1988 J e ep C hero ke e
GENERAL INFORMATION
Gear Tooth Contact Patterns
* PLEASE READ THIS FIRST *
The following article is for GENERAL INFORMATION purposes
only. Information does not SPECIFICALLY apply to all years, makes and
models, but is to be used as a general reference guide.
INSPECTION
PRELIMINARY INSPECTION
Wipe lubricant from internal parts. Rotate gears and inspect
for wear or damage. Mount dial indicator to housing, and check
backlash at several points around ring gear. Backlash must be within
specifications at all points. If no defects are found, check gear
tooth contact pattern.
GEAR TOOTH CONTACT PATTERN
NOTE: Drive pattern should be well centered on ring gear teeth.
Coast pattern should be centered, but may be slightly toward
toe of ring gear teeth.
1) Paint ring gear teeth with marking compound. Wrap cloth or
rope around drive pinion flange to act as brake. Rotate ring gear
until clear tooth contact pattern is obtained.
2) Contact pattern will indicate whether correct pinion
bearing mounting shim has been installed and if drive gear backlash
has been set properly. Backlash between drive gear and pinion must be
maintained within specified limits, until correct tooth pattern is
obtained.

Fig. 1: Drive Axle Gear Tooth Patterns
ADJUSTMENTS
GEAR BACKLASH & PINION SHIM CHANGES
NOTE: Backlash is adjusted by either moving shims from one side of
differential case to the other or by turning adjusting nuts
on which side bearing races ride. Changing of pinion shims
alters the distance from face of pinion of centerline of
ring gear.
1) With no change in backlash, moving pinion further from
ring gear moves drive pattern toward heel and top of tooth, and moves
coast pattern toward toe and top of tooth.
2) With no change in backlash, moving pinion closer to ring
gear moves drive pattern toward toe and bottom of tooth, and moves
coast pattern toward heel and bottom of tooth.
3) With no change in pinion shim thickness, an increase in
backlash moves ring gear further from pinion. Drive pattern moves
toward heel and top of tooth, and coast pattern moves toward heel and
top of tooth.
4) With no change in pinion shim thickness, decrease in

backlash moves ring gear closer to pinion gear. Drive pattern moves
toward toe and bottom of tooth, and coast pattern moves toward toe and
bottom of tooth.

GEN ER AL C O OLIN G S YSTE M S ER VIC IN G

1988 J e ep C hero ke e
GENERAL INFORMATION
General Cooling System Servicing
* PLEASE READ THIS FIRST *
The following article is for general information only.
Information may not apply to all years, makes and models. See specific
article in the ENGINE COOLING section.
DESCRIPTION
The basic liquid cooling system consists of a radiator, water
pump, thermostat, electric or belt-driven cooling fan, pressure cap,
heater, and various connecting hoses and cooling passages in the block
and cylinder head.
MAINTENANCE
DRAINING
Remove radiator cap and open heater control valve to maximum
heat position. Open drain cocks or remove plugs in bottom of radiator
and engine block. In-line engines usually have one plug or drain cock,
while "V" type engines will have 2, one in each bank of cylinders.
CLEANING
A good cleaning compound removes most rust and scale. Follow
manufacturer's instructions in the use of cleaner. If considerable
rust and scale has to be removed, cooling system should be flushed.
Clean radiator air passages with compressed air.
FLUSHING
CAUTION: Some manufacturers use an aluminum and plastic radiator.
Flushing solution must be compatible with aluminum.
Back Flushing
Back flushing is an effective means of removing cooling
system rust and scale. The radiator, engine and heater core should be
flushed separately.
Radiator
To flush radiator, connect flushing gun to water outlet of
radiator and disconnect water inlet hose. To prevent flooding engine,
use a hose connected to radiator inlet. Use air in short bursts to
prevent damage to radiator. Continue flushing until water runs clear.
Engine
To flush engine, remove thermostat and replace housing.
Connect flushing gun to water outlet of engine. Flush using short air
bursts until water runs clean.
Heater Core
Flush heater core as described for radiator. Ensure heater
control valve is set to maximum heat position before flushing heater.

REFILLING
To prevent air from being trapped in engine block, engine
should be running when refilling cooling system. After system is full,
continue running engine until thermostat is open, then recheck fill
level. Do not overfill system.
TESTING
THERMOSTAT
1) Visually inspect thermostat for corrosion and proper
sealing of valve and seat. If okay, suspend thermostat and thermometer
in a 50/50 mixture of coolant and water. See Fig. 1. Do not allow
thermostat or thermometer to touch bottom of container. Heat water
until thermostat just begins to open.
2) Read temperature on thermometer. This is the initial
opening temperature and should be within specification. Continue
heating water until thermostat is fully open and note temperature.
This is the fully opened temperature. If either reading is not to
specification, replace thermostat.
Fig. 1: Testing Thermostat in Anti-Freeze/Water Solution
PRESSURE TESTING
A pressure tester is used to check both radiator cap and

complete cooling system. Test components as follows, following tool
manufacturer's instructions.
Radiator Cap
Visually inspect radiator cap, then dip cap into water and
connect to tester. Pump tester to bring pressure to upper limit of cap
specification. If cap fails to hold pressure, replace cap.
Fig. 2: Testing Radiator Pressure Cap
Cooling System
1) With engine off, wipe radiator filler neck seat clean.
Fill radiator to correct level. Attach tester to radiator and pump
until pressure is at upper level of radiator rating.
2) If pressure drops, inspect for external leaks. If no leaks
are apparent, detach tester and run engine until normal operating
temperature is reached. Reattach tester and observe. If pressure
builds up immediately, a possible leak exists from a faulty head
gasket or crack in head or block.
NOTE: Pressure may build up quickly. Release any excess pressure
or cooling system damage may result.
3) If there is no immediate pressure build up, pump tester to
within system pressure range (on radiator cap). Vibration of gauge
pointer indicates compression or combustion leak into cooling system.
Isolate leak by shorting each spark plug wire to cylinder block. Gauge
pointer should stop or decrease vibration when leaking cylinder is
shorted.

HEA TE R S YSTE M T R O UBLE S H O OTIN G

1988 J e ep C hero ke e
1989 HEATER SYSTEMS
Eagle Trouble Shooting
CONDITION & POSSIBLE CAUSE
Little or No Air From Heater Floor Outlets.
* Misadjusted heater air door cable.
* Obstructed heater housing or ducts.
* Clogged heater core fins.
* Leaking air duct seals.
Little or No Air From Defroster Outlets.
* Defroster duct misaligned.
* Defroster cable incorrectly adjusted
* Leaking air duct seals.
* Defroster duct damaged.
Heat Output When Controls Are Off.
* Outside air cable misadjusted
* Outside Air door binding in housing.
Not Enough Heat With Controls Fully On.
* Low coolant or plugged heater core.
* Incorrect thermostat.
* Incorrect adjustment of cables.
* Heater System Air Leaks.
* Blend air door not in proper position.
Blower Will Not Run.
* Blown fuse.
* Loose connections or poor ground.
* Faulty switch, motor or resistor.
Blower Runs But Does Not Circulate Air.
* Intake blocked..
* Fan not attached to motor shaft.

HEA TE R S YSTE M

1988 J e ep C hero ke e
1988 HEATER SYSTEMS
Jeep
DESCRIPTION
Jeep vehicles use a blend-air type heater system. Wrangler
models have a constant flow type system with engine coolant
continuously flowing through heater core. Cherokee and Comanche use
heater control valves. Coolant flow to heater core on these models can
be stopped or diverted.
On all models, temperature of heated air entering passenger
compartment is controlled by regulating amount of air flowing through
heater core and then blending it with a controlled amount of cool air
by-passing heater core.
CONTROL PANEL OPERATION
Control panel on all models includes fan switch, sliding
temperature control lever and sliding mode lever.
DEFROSTER CONTROL
Defroster control operates heater housing door regulating
heater and defroster operation by directing flow of air through
defroster hose or floor outlets. When control knob is pushed in,
blended air will enter passenger compartment through floor heat duct.
When control is pulled completely out, door directs all heated air to
windshield defroster outlets. Any intermediate position divides air
flow between windshield and floor outlets.
TEMPERATURE CONTROL LEVER (CHEROKEE, COMANCHE & WRANGLER)
Lower control lever operates blend-air door in heater core
housing. At full right position, all air is directed through heater
core, providing maximum heat flow. At full left position, all air is
directed around heater core providing fresh air. Control can be set in
any intermediate position to provide a blend of heated and unheated
air. With control lever in "COOL" position, water valve will close
(except Wrangler). Mode control lever must be in "HEAT" or defroster
mode before any air can enter vehicle.
MODE CONTROL LEVER (CHEROKEE & COMANCHE)
Mode control lever includes "BI-LEVEL", "VENT", "HEAT" and
"OFF" positions. At far end of scale, a symbol for defroster indicates
defrost position. In "BI-LEVEL" position, a mixture of floor heat and
defroster air is obtained.
FAN CONTROL
Fan control is a 4-position control switch, regulating blower
motor and air flow for heat and defrost. Switch has "LOW", "HIGH" and
2 intermediate positions. Fan will remain on unless mode lever is
placed in "OFF" position.
CONTROL CABLES ADJUSTMENT

CHEROKEE & COMANCHE
The heater control cable is retained to blend air door lever
with a retaining clip and a self-adjusting clip. During installation,
self-adjusting clip will locate cable properly when cable is snapped
into position on lever.
WRANGLER
The only adjustable cables are the vent door control cables.
Since the left cable operates the right cable, the cables must be
installed and adjusted in the proper order to maintain the self
adjusting mechanism.
With cables connected to heater control panel, connect only
the right vent door cable. Open and close right vent door one time,
using heater control panel. Connect left side cable and ensure that
both vent doors open at the same time.
Fig. 1: Heater & Defroster Components (Wrangler)
Courtesy of Chrysler Motors.

Fig. 2: Typical Heater & Defroster Components
Courtesy of Chrysler Motors.
BLOWER MOTOR R & I
NOTE: On Cherokee and Comanche, blower motor and fan are removed
from engine compartment.
Removal & Installation
1) Remove heater core housing assembly. On all models, remove
blower motor electrical connectors. Detach screws retaining blower
motor assembly to heater housing. Remove blower motor and fan
assembly. On Cherokee and Comanche, detach fan retaining clip from fan
hub, if necessary. Remove fan from motor shaft.
2) To install, reverse removal procedure. If removed, ensure
ears of retaining clip are over flat surface on motor shaft. Check
blower motor and heater operation.
CONTROL PANEL R & I
Removal & Installation
1) Disconnect battery ground. On Cherokee, remove lower
instrument panel. On all models, remove instrument panel bezel. On
Cherokee, remove clock and radio (if equipped).
2) On all models, remove heater control panel attaching
screws. Pull out control panel and disconnect vacuum hoses, wires and
cables. Note locations for reassembly reference. Remove control panel.
To install, reverse removal procedure.
CONTROL CABLES R & I
REMOVAL (CHEROKEE & COMANCHE)
Remove control panel. Detach cable from heater control panel.