TRANSFER CASE - COMMAND TRAC DIAGNOSIS
1988 Jeep Cherokee
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.
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).
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.
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
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
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
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.
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)
support vehicle. Position a drain pan under
shift motor housing.
Disconnect vacuum harness.
housing attaching bolts. Remove housing, motor and
shift fork as a unit. See Fig. 3.
Mark shift fork and housing for installation reference.
shift motor and remove shift fork and motor
retaining snap rings.
Remove shift motor from housing.
O-ring seal from shift motor shaft. See Fig. 4.
Discard O-ring seal.
INSTALLATION (60/70 SERIES AND MODEL 81 VEHICLES)
5 ounces (148 ml)
of SAE 75W-90 grade GL 5 gear
lubricant to axle through shift motor housing opening.
a replacement O-ring seal on shift motor shaft.
See Fig. 4.
shift motor in housing with retaining snap rings
and slide shift fork onto shaft with reference mark aligned.
shift fork with shift collar and install housing
attaching bolts. See Fig. 3. Tighten bolts with 101 inch-lbs. (11 N.m)
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