How to Convert a Standard Axle to a Posi

by Timothy Burns

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Positive traction differentials, sometimes referred to as posi-tracs, or posi diffs, change the performance characteristics of a rear-wheel-drive car's differential. The differential allows the rear wheels to turn at different rates when the car goes around a corner, and delivers drive force to the wheel with the least amount of resistance. A positive traction differential applies drive force to each wheel equally, even if the wheels are spinning at different rates, or if one wheel slips on stones or ice.

Step 1

Don your safety equipment, including gloves and safety glasses.

Step 2

Lift the car with the jack, and support the car on jack stands so you can access it with the creeper. Never begin work under a car without supporting the vehicle on a pair of solid, metal jack stands or a hydraulic lift.

Step 3

Drain the fluid from the rear differential by removing the drain plug. If the drain plug is above the oil level, use a suction pump and remove the liquid form the differential before opening the cover. Catch the oil in a pan, and dispose of it properly at a recycling center.

Step 4

Remove the differential cover by removing the bolts around the perimeter of the cover. Catch any remaining oil in the oil pan.

Step 5

Unbolt and remove accessible parts from the differential. Some of the internals are not accessible until the axles are removed in the next step. Remove the pieces which disconnect the rear axles and allow you to pull the axles.

Step 6

Remove both the rear wheels, brake drums, axle nuts, axle bearings. Set all the bearings and bearing cones into a container of grease-cutting solvent, and place it aside. Set the brake parts in a safe place as well. You will reinstall the parts after the differential is converted.

Step 7

Remove axle retention rings, and pull the axles outward from the differential about 6 to 12 inches.

Step 8

Unbolt the remaining internals from the differential and remove the rest of the internals. Unclip the retention ring on the pinion gear that is attached to the drive shaft, and remove the pinion gear too.

Step 9

Install the new internals in the reverse order. Bolt the posi-traction upgrade kit into place. Push the axles back into place, replacing any worn parts during the rebuilding process. Apply high-quality wheel bearing grease and reinstall the wheel bearings, brakes and wheels according to the manufacturer's instructions. Insert the remaining parts of the posi-traction upgrade kit into the differential, and bolt all the parts into place.

Step 10

Install a new rear differential gasket. Coat both sides of the gasket with silicone gasket material and replace the differential cover. Replace the bolts around the perimeter, and be careful not to over-torque them. These bolts will snap off easily if wrenched too aggressively. You will have the best results using a torque wrench, and setting the bolts to factory specs.