1988 Jeep Cherokee

1988 Locking Hubs - Command-Trac & Selec-Trac Jeep


Command-Trac locking hub is used on Model 30 front axles. This system can be shifted between 2WD and 4WD high range while vehicle is moving. The only time vehicle must be stopped to shift into or out of 4WD is when shifter is in low range. See Fig. 1.

Selec-Trac locking hubs allow full or part time 4WD. Used on Model 30 front axles, system can be shifted into 2WD or 4WD modes only when vehicle is stopped. See Fig. 2.

Vacuum Reservoir

Fig. 1: Command-Trac Vacuum Control System



2WD To 4WD

Position mode select switch to "4WD" position while driving vehicle 2-3 MPH. Axle should ratchet and clunk into position. Transfer case should shift after axle shifts, accompanied by hissing sound from mode selector switch.

4WD To 2WD

1) Position mode select switch to "2WD" position. Transfer case should shift to 2WD and not allow shifting into 4WD or "LO" range. Axle should shift after transfer case shifts.

2) To determine if front axle has completed a shift out of 4WD into 2WD, position mode select switch back to "4WD" position while operating vehicle at slow speed. If vehicle shifts into 2WD, axle will ratchet. If shift is not completed, transfer case will shift into 4WD and hissing sound will come from mode select switch.


  1. Disconnect vacuum harness from front axle shift motor.
    Connect vacuum pump to shift motor front port. Apply 15 in. Hg vacuum
    to shift motor. Rotate right front wheel to disengage axle.

  2. Shift motor should hold vacuum at least 30 seconds. If
    not, replace motor. If motor does hold vacuum, disconnect vacuum pump
    from shift motor front port. Connect pump to shift motor rear port and
    cap transfer case connecting port. Apply 15 in. Hg vacuum to motor.

  3. Shift motor should hold vacuum for at least 30 seconds. If
    not, replace motor. If motor does hold vacuum, remove cap from shift
    motor transfer case connecting port and check for vacuum. If no vacuum
    is present, rotate right front wheel to ensure axle has shifted
    completely. Axle must completely shift to open shift motor connecting

  4. Recheck vacuum at shift motor transfer case port. If
    vacuum is present, transfer case requires diagnosis. Command-Trac uses
    Model 207 transfer case. Selec-Trac uses Model 228 transfer case.




  1. Remove cover to outer clutch housing. Remove bearing race
    spring assembly. Remove sealing ring and seal bridge retainer. Remove
    bearing components.

  2. Squeeze tangs of wire retaining ring together with needle-
    nose pliers. Pull remaining components of automatic hub from wheel.


1) Ensure lock ring is in position. Using Bearing Nut Wrench
(J-6893-D), tighten wheel bearing adjusting nut to
50 ft. lbs. (60 N.

m) to seat bearings.

32466 Vanuum Shift Motors

Fig. 2: Selec-Trac Vacuum Control System


  1. Back off nut and tighten to 35 ft. lbs. (47 N.m) while
    rotating hub. Finally, back off nut a maximum of 3/8 turn. Assemble
    lock ring (with tab in keyway) over axle shaft, against bearing
    adjustment nut.

  2. Adjustment nut pin must pass through one of the washer
    holes. Tighten outer adjusting nut to 183 ft. lbs. (248 N.m). Align
    outer clutch housing splines with splines of wheel hub.

  3. Loosen cover screws 3 or 4 turns, and push in on cover to
    allow retaining ring to expand into rotor hub groove. Tighten cover
    cap screws to 40-50 INCH lbs. (4.5-5.6 N.m).


  1. Raise and support vehicle. Drain shift housing fluid.
    Disconnect vacuum harness. Remove housing bolts. Remove motor and
    housing. Mark shift fork and housing for reassembly. See Fig. 3.

  2. Rotate shift motor. Remove shift fork and motor snap
    rings. Remove shift motor from housing. Remove "O" ring from motor.
    Always use a new "O" ring for reassembly.


Install new "O" ring on motor shaft. Install motor into

housing and slide shift fork onto shaft. Position motor and housing on axle. Add axle lubricant to shift motor housing. Install shift fork in shift collar and install housing bolts. Connect all vacuum harnesses to motor.


Fig. 3: Shift Motor & Housing