1. Identify Your Hub Type:
* Automatic Locking Hubs: These hubs automatically engage when you select 4WD. You'll see no manual controls on the hubs themselves. They are usually integrated with the wheel bearing assembly.
* Manual Locking Hubs: These hubs require you to manually lock them *before* engaging 4WD. They usually have a lever or knob on each front wheel hub. These will be labeled something like "free" (2WD) and "lock" (4WD).
2. Engaging 4WD (Assuming you've locked manual hubs if applicable):
* Transfer Case Lever: Your GMC Jimmy will have a transfer case lever located either on the floor or on the column (steering column). This lever controls the engagement of the front driveshaft. The positions will be something like:
* 2WD (2H or 2 wheel High): Rear-wheel drive only. This is for normal driving on paved roads.
* 4WD High (4H or 4 wheel High): Engages all four wheels for improved traction on slippery surfaces or off-road. *Use this on dry pavement only at low speeds, otherwise it can damage the drivetrain*.
* 4WD Low (4L or 4 wheel Low): Engages all four wheels with a lower gear ratio, providing significantly more torque for off-roading, steep inclines, or heavy towing. *Never use 4L on dry pavement; it will damage the drivetrain*.
* Neutral (N): Disengages the driveshaft from the transmission.
* Procedure (with Manual Locking Hubs):
1. Stop the vehicle completely before engaging 4WD.
2. Lock the front hubs: Turn the hubs to the "LOCK" position on each front wheel.
3. Select 4H or 4L: Shift the transfer case lever to the appropriate position (4H for light off-road or slippery conditions; 4L for difficult off-road conditions).
* Procedure (with Automatic Locking Hubs):
1. Stop the vehicle completely before engaging 4WD.
2. Select 4H or 4L: Shift the transfer case lever to the appropriate position.
Important Considerations:
* Speed: Never engage or disengage 4WD while the vehicle is moving, except for very slow speeds (usually under 5mph). Doing so can severely damage the drivetrain.
* Surface: Only use 4WD when needed. Driving on dry pavement in 4WD can cause excessive wear and tear on your drivetrain components. Use 4L only at low speeds.
* Consult your owner's manual: This is the best resource for specific instructions on your vehicle's 4WD system. It will detail the exact location and operation of the transfer case lever and the type of hubs your Jimmy has.
If you're unsure about anything, consult your owner's manual or a qualified mechanic. Incorrect 4WD operation can lead to costly repairs.
