Reference: 'Jeep' Magazine, 1986

Four wheel drive. To the off-road enthusiast four wheel drive means freedom; freedom to go most anywhere he wants, just for the fun of it. For other motorists it means security- optimum traction and maximum driving safety under the most adverse and varied road conditions. With the advances made in four-wheel driveline technology, whichever type of driver you are, you now have options that you would do well to explore. Namely, will a part-time system fit your needs or will a full-time system be better?

WHY FOUR-WHEEL DRIVE?
Before exploring the differences of each system, let's explain why you need four-wheel drive. First, wheels are not used only to allow movement of your vehicle, they are the medium through which you control it. Your vehicle's tires provide support and stability, much like the four legs of a table. They transmit power to the road by way of traction, provide braking power and resist lateral movement, which allows your vehicle to run straight as well as handle corners well.  There should also be provisions to allow the individual wheels to rotate as needed, independent of each other. This is necessary to avoid driveline bind caused by the different distances of wheel travel when you are turning or executing other driving manoeuvres.

COMMAND-TRAC: PART-TIME FOUR-WHEEL DRIVE

Jeep's standard four-wheel drive system with the convenience of auto-locking hubs and shift-on-the-fly capability. This means you can engage the front axle and wheels at any speed without getting out of the vehicle to lock the hubs.

Part-time four-wheel drive is designed specifically for off-road use or extremely low traction situations on paved roads. Because of the generally slow speeds, low traction and resultant wheel slip, the rigid driveline isn't

Command-Trac is one of Jeep's part-time four-wheel drive systems. Jeep uses the New Process 207 transfer case in the Cherokee, Wagoneer, Comanche and Wrangler. Command-Trac does not incorporate a centre differential and should only be used off-road or in extremely low-traction situations on pavement subject to binding (driveline bind causes tire and mechanical wear as the vehicle speed increases). Although on non-slip surfaces, driveline bind does occur because there is no differential compensation between the front and rear axles.

SELEC-TRAC: FULL-TIME FOUR-WHEEL DRIVE

Jeep's full-time , or all-surface, system uses a centre differential that automatically and continuously distributes torque to the axle with the most traction. In demanding situations, the rear wheels push and the front wheels pull. On dry pavement, the centre differential eliminates driveline bind.