Every diesel truck on the road today has a differential and ring and pinion gear set in the rear axle. Four-wheel-drive trucks add a second set of gears and another differential to the front axle to transmit engine torque to all four wheels. Yet differential modification and repair is one of the most feared and least understood aspects of diesel trucks.

The truth is, setting up ring and pinion gears and installing traction-adding differentials isn't hard-but it is a pain and requires special tools that can mean a big investment of cash. To see how difficult installing new gears and a differential would be at home, we chose a Dana 50 front differential from a Ford F-250 to use as a guinea pig.

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