1988 JEEP CHEROKEE Service Repair Manual

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TR AN SFE R C ASE - C O M MAN D T R AC D IA G NO SIS

1988 J e ep C hero ke e
1984-90 Drive Axles - Transfer Case - Electronic Diagnosis
Cherokee, Wagoneer, Wrangler (1987-90)
VACUUM CONTROL SYSTEM
The Command-Trac vacuum switch consists of a vacuum control
switch on the transfer case, an air vent filter, a vacuum shift motor
(located on front axle), a four-wheel drive indicator light and vacuum\
switch, two vacuum check valves and an interconnecting vacuum harness.
See Fig. 1 .
Fig. 1: Command-Trac Vacuum Control System
AXLE SHIFT MOTOR FUNCTIONAL TEST
1) Raise vehicle. Disconnect vacuum harness from axle shift
motor and connect a vacuum pump to vacuum shift motor port. See
Fig. 2 .

2) Apply 15 in. Hg. (51 kPa) of vacuum to front port and
rotate right front wheel to fully disengage outer and intermediate
axle shafts (i.g., into two wheel drive operation).
3) The shift motor should maintain vacuum applied to front
port for a minimum of 30 seconds. If motor does not maintain vacuum,
replace it. If motor does maintain vacuum, proceed to next step.
4) Disconnect vacuum pump from vacuum shift motor front port.
See Fig. 2 . Connect vacuum pump to vacuum shift motor rear port, cap
port for indicator lamp sw., and apply 15 in. Hg (51 kPa) of vacuum to\
rear port.
5) The shift motor should maintain the vacuum applied to rear
port for a minimum of 30 seconds. If shift motor does not maintain
vacuum, replace it. If motor does maintain vacuum, proceed to next
step.
6) Remove cap from port for indicator lamp sw. and determine
if vacuum was present at this port. If vacuum was present, the shift
motor functions normally. If vacuum was not present, proceed to next
step.
7) Apply 15 in. Hg. (51 kPa) of vacuum to shift motor rear
port. Rotate right front wheel as necessary and ensure that outer and
intermediate axle shafts are completely engaged. The axles must be
completely engaged (i.e. into four-wheel drive operation) to open port\
for indicator lamp switch.
8) Determine if vacuum is present at port for indicator lamp
switch again. If vacuum was present at por, shift motor functions
normally. If vacuum was not present at port, replace shift motor.
Fig. 2: Axle Vacuum Shift Motor
AXLE SHIFT MOTOR AND HOUSING REMOVAL & INSTALLATION

REMOVAL (60/70 SERIES AND MODEL 81 VEHICLES)
1) Raise and support vehicle. Position a drain pan under
shift motor housing.
2) Disconnect vacuum harness.
3) Remove housing attaching bolts. Remove housing, motor and
shift fork as a unit. See Fig. 3.
4) Mark shift fork and housing for installation reference.
5) Rotate shift motor and remove shift fork and motor
retaining snap rings.
6) Remove shift motor from housing.
7) Remove O-ring seal from shift motor shaft. See Fig. 4.
Discard O-ring seal.
INSTALLATION (60/70 SERIES AND MODEL 81 VEHICLES)
1) Add 5 ounces (148 ml) of SAE 75W-90 grade GL 5 gear
lubricant to axle through shift motor housing opening.
2) Insatll a replacement O-ring seal on shift motor shaft.
See Fig. 4 .
3) Insatll shift motor in housing with retaining snap rings
and slide shift fork onto shaft with reference mark aligned.
4) Engage shift fork with shift collar and install housing
attaching bolts. See Fig. 3. Tighten bolts with 101 inch-lbs. (11 N.m)
torque.
5) Connect vacuum harness to shift motor and lower vehicle.
Fig. 3: Axle Vacuum Shift Motor and Housing

Fig. 4: Axle Vacuum Shift Motor Shaft O-Ring Seal

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TR AN SFE R C ASE - O VER HAU L ( 2 07/2 31)

1 988 J e ep C hero ke e
1983-96 TRANSFER CASES
Chrysler Corp., GM Corp., Jeep - New Process 207 & 231
Dodge; B1500 & Dakota
GMC/Chevrolet; "T" Series (Blazer & Jimmy)
Jeep; Cherokee, Comanche, Grand Cherokee, Wagoneer, Wrangler
IDENTIFICATION
Transfer case can be identified by an I.D. tag, located on
rear case. I.D. tag provides model number, serial number and low range
ratio. Date of manufacture is the serial number (I.D. number). This
information is necessary when ordering parts.
DESCRIPTION
Model 231 transfer case is a part time, chain-driven, 4-
position unit with 2-piece aluminum case. Torque input in 4WD high and
low range is undifferentiated. 2WD operation is achieved by a vacuum
shift motor. Shift motor disconnects right front axle when 2WD is
selected. Vacuum shift motor is controlled by a vacuum switch located
on front of transfer case and actuated by shift sector.
ADJUSTMENTS
GEARSHIFT LINKAGE
Chrysler Corp.
Shift transfer case to 2H position. Raise and support
vehicle. Loosen lock bolt at trunnion. Ensure linkage rod slides
freely in trunnion. Verify transfer case range lever is fully engaged
in 2H position. Tighten lock bolt at trunnion. Lower vehicle. Check
shift linkage operation. Ensure transfer case shifts into and operates
properly in all gear ranges.
General Motors
Remove shift lever knob retainer. Remove shift lever knob.
Remove floor console. Place shift lever in Neutral. Pry control cable
end from shift lever. Loosen control cable lock nut. Check transfer
case to ensure it is in Neutral. Ensure shift lever is in Neutral.
Turn shift lever end of cable in or out as needed until it is aligned
with shift lever. Install control cable on shift lever. Tighten
control cable lock nut.
Jeep
Shift transfer case to 4L position. Raise and support
vehicle. Loosen lock bolt at trunnion. Ensure linkage rod slides
freely in trunnion. Verify transfer case range lever is fully engaged
in 4L position. Tighten lock bolt at trunnion. Lower vehicle. Check
shift linkage operation. Ensure transfer case shifts into and operates
properly in all gear ranges.
TESTING
VACUUM SWITCH
Shift to 2WD position. Locate vacuum switch on front of

transfer case. Apply 15 in. Hg vacuum to "L". See Fig. 1. Vacuum
should be present at "M". Connect a vacuum gauge to "N". Shift to 4WD
position. Apply vacuum to "L". Vacuum should be present at "N". If
switch fails any test, replace switch.
Fig. 1: Testing Vacuum Switch
Courtesy of Chrysler Corp.
TROUBLE SHOOTING
SYMPTOM DIAGNOSIS

Will Not Shift Or Difficult To Shift Into Gear
Vehicle speed too high; slow vehicle to 2-3 MPH to shift.
Vehicle operated too long on dry paved surface; stop vehicle and place
in Reverse or Neutral to relieve driveline torque. Ensure transfer
case external linkage is not binding. Ensure correct fluid is used.
Internal parts may be worn or damaged.
Noisy In All Gears
Check fluid level. Ensure correct fluid is used. If fluid is
okay, locate possible internal mechanical problem.
Jumps Out Of Gear Or Noisy In 4WD
Transfer case not completely in gear; check shift linkage.
Range fork damaged. Shift fork pads are worn or shift fork binding.
Low range gear worn.
Fluid Leaking From Vent Or Seals
Transfer case overfilled. Vent plugged. Output shaft seals
are damaged or not installed properly.
ON-VEHICLE SERVICE
FRONT OIL SEAL
Removal & Installation
1) Mark front drive shaft and flange for installation
alignment reference. Remove front drive shaft. Remove flange. Discard
washer and nut. Using a screwdriver, carefully remove oil seal. Ensure
seal contact surface is clean.
2) Apply ATF to seal lip and flange seal surface. Install NEW
oil seal. Install flange and NEW washer and nut. Tighten nut to
specifications. See TORQUE SPECIFICATIONS . Install front drive shaft
using alignment marks. Check transfer case fluid.
EXTENSION HOUSING OIL SEAL & BUSHING
Removal & Installation
1) Mark rear drive shaft and flange for installation
alignment reference. Remove rear drive shaft. Tap extension housing in
a clockwise direction and remove extension housing. DO NOT pry on
extension housing. Using a screwdriver, remove oil seal from extension
housing.
2) Using bushing driver, replace bushing in extension
housing. Install NEW extension housing oil seal. Apply silicone
sealant to extension housing mating surface. Install extension
housing. To complete installation, reverse removal procedure.
REMOVAL & INSTALLATION
TRANSFER CASE
Removal
1) Shift transfer case into 4H and disconnect battery
negative cable. Raise vehicle, remove skid plate and drain fluid.
2) Mark front and rear output shaft yokes to drive shafts for
reassembly reference. Support transfer case and remove rear
crossmember. Remove drive shafts.
3) Disconnect vehicle speed sensor electrical connector and
vacuum (hoses) harness at transfer case. Remove shift lever or linkage\
rod from case. Remove transfer case attaching bolts. Remove transfer
case from vehicle.

Installation
1) Clean all old gasket material from transmission and
transfer case mating surfaces. Position NEW gasket on transfer case
with orientation tab at upper left bolt hole.
2) Install transfer case, aligning splines of input shaft
with transmission. Slide transfer case forward until seated against
transmission. Install transfer case attaching bolts and tighten to
specification. See TORQUE SPECIFICATIONS . Install rear crossmember.
3) Attach shift lever and connect speed sensor electrical
connector and vacuum harness at transfer case. Using reference marks
made during removal, reinstall front and rear drive shafts. Refill
transfer case. Install skid plate and lower vehicle. Connect negative
battery cable. Road test vehicle.
TRANSFER CASE DISASSEMBLY
1) Remove front companion yoke. See Fig. 2 or 3. Discard
washer and nut. Shift transfer case to 4L and remove extension
housing. Remove rear bearing snap ring. Using 2 screwdrivers under
each tab, remove retainer housing. Remove rear case and oil pump as an
assembly.
2) Remove oil pump pick-up screen and tube from rear case.
Remove oil pump. Remove "O" ring from oil pump and discard. DO NOT
separate oil pump halves. Pump must be replaced as an assembly if
necessary.
3) Remove mode spring. Using a soft hammer, tap front output
shaft upward and remove with drive chain as an assembly. Remove
mainshaft, mode fork and shift rail as an assembly. Remove mode fork
and shift rail from synchronizer sleeve.
4) Mark synchronizer sleeve position for reassembly
reference. Remove synchronizer sleeve from mainshaft. Remove
synchronizer hub snap ring. Remove synchronizer hub, stop ring and
drive sprocket. Slide range fork pin out of sector.
5) Remove range fork and shift hub as an assembly. Remove
range lever from sector shaft. Remove shift sector, bushing and "O"
ring. Remove shift detent pin, spring and plug. Remove front bearing
retainer. Remove input gear snap ring.
6) Press input and low range gear assembly from input gear
bearing. Remove low range gear snap ring. Remove input gear retainer,
thrust washers and input gear from low range gear.
7) Remove all oil seals. Remove magnet from front case.
Remove front bearing snap ring. Using a plastic hammer, remove front
bearing. Press input gear bearing from front case.
8) Using slide hammer and internal puller, remove input gear
pilot bearing. Press bearings from drive sprocket. Using internal
puller and slide hammer, remove output shaft rear bearing.