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Although it does not happen very often, from time to time the differential in a rear wheel drive car will fail and the ring gear will need replacement. Replacing the ring gear is a job normally left to professional technicians because of the tools and knowledge needed to measure the precise tolerances during reassembly. However, a do-it-yourselfer with some advanced skills can do the job at home.

Instructions

Preparing the Vehicle

1

Place a wheel chock in front of each of the front tires. Center the lifting pad of a floor jack under the differential. Jack up the vehicle until the floor deck supports the weight of the vehicle, and the rear wheels are still in contact with the ground.

2

Turn the lug nuts, which hold the tires to the vehicle, counterclockwise with a lug wrench to loosen them. Just loosen the lug nuts, do not remove them.

3

Jack up the vehicle with the floor jack until the tires are no longer are in contact with the ground. Place a jack stand under each axle tube and lower the vehicle so that the rear axle tubes rests on the jack stands. Adjust the jack stands high enough that the rear wheels are still off the ground when the vehicle is resting on them by pulling the ratcheting center post of each jack stand up as close to the axle tube as it will go.

4

Remove the lug nuts and tires from the vehicle.

Removing the Axle Shafts

5

Place a drain pan underneath the differential. Turn the differential cover bolts counterclockwise using the appropriate size socket on a ratchet wrench. Drive a screwdriver between the cover and the differential by gently tapping it with a hammer to break the seal, and remove the differential cover allowing the gear lube in the differential to drain into the drain pan.

6

Turn the bolt that secures the cross pin counterclockwise with the ratchet wrench and appropriate size socket to remove it. Remove the cross pin.

7

Push each axle shaft in from the outside and remove the C-clip from the other end of each axle shaft. Remove the axle shafts from the vehicle by pulling them straight out from the outside.

Removing the Ring Gear

8

Make an identification mark on each of the carrier caps with the center punch and hammer to ensure the carrier caps are reassembled in their original positions.

9

Remove the upper and lower bolts from each carrier cap and remove the caps. Remove the carrier and ring gear assembly from the differential.

10

Turn the bolts that attach the ring gear to the carrier counterclockwise with a ratchet wrench and appropriate socket to remove them. Remove the ring gear, completing the operation.

A cars differential receives the torque force generated by the engine and transmission, via the driveshaft, and distributes it to the driven wheels. The differential uses gears to reduce the speed of the input force -- the engine spins at higher RPMs than the wheels. The difference between the input speed and the output speed is called the final gear ratio. Every BMW differential has the final gear ratio stamped on it, as well as a letter designating whether it is an open or limited-slip differential. Depending on the year and model of your BMW, the stamp may be on either side or the rear of the differential, typically found on a flat area adjacent to a bolt. Since BMWs are performance-oriented cars, it may be necessary to raise the rear of the vehicle in order to view the stamping.

Instructions

1

Raise the vehicle using a floor jack, and place it securely on jack stands if necessary.

2

Locate the differential between the two rear tires. Depending on the year and model, the stamp may be on the either side or on the rear of the differential. Look for a flat, smooth area next to a bolt, with a series of letters and numbers stamped on it.

3

Clean the stamping using a rag and wire brush, if necessary. Depending on the age and use of the vehicle, a significant amount of grime may have accumulated.

4

Decode the stamping. It will be comprised of eight characters. The first is a letter, most likely an N or R, which designates an open differential. The letter S signifies a limited-slip differential. After that will be three digits, such as 345. This indicates a final drive ratio of 3.45:1. After that will be four digits, such as 0722, which refer to the part number of the differential.

Starting your Harley-Davidson Ironhead motorcycle is often taken for granted. You get on the bike, turn on the fuel and ignition and give it a kick to bring the motor to life. All goes well until the day when you go to kick start the bike and the kicker gear fails, leaving you stranded with no way to start the engine. Replacing a broken or worn out gear is time consuming, but well within the abilities of the average home mechanic. You can save hundreds of dollars of expensive shop time by doing the job yourself.

Instructions

1

Disconnect the battery negative (-) cable. Remove the kick starter pedal and both foot pegs. Remove the gearshift lever and remove the rear brake master cylinder from the frame, but do not disconnect the hydraulic hose.

2

Place a drain pan underneath the primary chain cover. Remove the chain case drain plug to drain the chain case oil. Remove the chain case cover and the gasket.

3

Install the spring compression tool H-D 97178-71 onto the crankcase and compress the releasing disc. Remove the retaining nuts, disc and inner and outer clutch springs. Remove the spring compression tool from the crankcase.

4

Remove the outer drive plate and all the friction and inner driven plates. Store the plates in the order they were removed. Remove the pressure plate and chain adjuster. Remove the clutch hub nut and lock-washer and remove the clutch hub.

5

Loosen the exhaust pipe and muffler. Remove the sprocket cover and rotate the crank gear until the starter clutch gear falls free. Remove the shaft nut and lock-washer. Tap the end of the kick starter shaft to loosen the crank gear. Remove the crank gear, kick-starter shaft, oil seal, thrust plate and shims.

6

Inspect the kick starter gears and shafts for wear and damage. Replace as required. Install the kick starter in the reverse order of disassembly. Torque the kicker gear nut to 55 to 65 ft-lbs. and use a new lock-washer.