Ring and pinion gears obviously need to be changed if they are broken, but racers often change ring and pinion gears as different gearing increases or decreases torque at lower speeds (increasing or decreasing acceleration). The way to accurately determine what gear ratio is currently installed is to count the number of teeth on the ring gear and the pinion. Divide the number of pinion teeth into the number of ring gear teeth and the answer is the current gear ratio. If, for example, the gear ratio was a 3.73, the driveshaft will turn 3.73 times for 1 revolution of the tire. The higher the gear ratio, the higher the engine rpm will be at 60 mph. In addition, the higher the gear ratio, the faster the acceleration from a stop.
Raise the rear of the vehicle and support it on jack stands. Put the jack stands under the frame, not the rear axle. Put the transmission in neutral.
Remove the rear wheels using the ½-inch air gun and the appropriate socket.
Disconnect the drive shaft by taking the bolts out of the clamps or nuts on the u-bolts on the universal joint, depending on which it may be. Use the screwdriver to pry the universal joint out of its cradle and lay the driveshaft end down. Do not remove the driveshaft from the transmission.
Remove the large pinion nut with the ½-inch air gun and the appropriate socket. Usually it is a 1-1/16-inch socket (size depends on year, make and model of the vehicle).
Place the drip pan under the rear cover and remove the 13mm bolts on the cover with the 3/8-inch ratchet and 13mm socket. Use the screwdriver to pry the cover loose slowly and allow the oil to run into the drip pan. Pull the cover off and let it drain.
Remove the rear drums if the vehicle has drum brakes. The drums simply slide off. If you have trouble pulling them off, whack them once or twice with a hammer.
Rotate one of the axles to turn the center carrier so the center pin with the small 8mm lock bolt is facing the bottom opening of the carrier housing. Look at the carrier and the large pin that runs through the center and through the spider gears---place this end with the small bolt so that the bolt can be removed and the pin can be slid out.
Unscrew the small lock bolt with an 8mm socket and ratchet. Vehicles will vary---the 8mm is common but not the rule. Just use the right socket. Pull the lock bolt out and the large pin can be slid out the bottom. Push both axles in by hand as far as they will go.
Remove the large c-clips on the inside ends of the axles with the magnet. Once the c-clip is removed, pull each axle out half way, leaving them in the axle tube. Put the center pin back into the carrier so that the spider gears do not come out of place. Install the small lock bolt loosely.
Pull the pinion yoke off by hand. If it is stubborn, use the hammer to give it some help. Tap it on the backside toward the front. Remove the two vertical clamps on both sides of the carrier---these are used to hold the carrier in but cover the outside of the bearings. Use the ½-inch air gun and the right size socket.
Remove the center carrier by prying it out, if necessary, with the screwdriver, and lay it on something clean. Be careful: the carrier is heavy and slippery with oil, personal injury could result. It is important to keep the bearing shims separated and isolated to each side of the carrier. They are of different thickness and must go into the same side they came out of. Place the left shims to the left and the right to right.
Pull the pinion out through the back of the housing. It should come out with a crush collar also, if not grab the crush collar left behind in the housing and pull it out.
Place the new pinion into the housing from the backside opening if it already came with a pinion bearing. Usually they do not come with a pinion bearing so a new pinion bearing must be purchased. The old bearing must come off of the old pinion. This is not to be reused, but the shims that lay behind it must be installed on the new pinion before the pinion bearing is pressed on or it will not line up properly with the ring gear. Have the shims and new bearing pressed on at the machine shop and then install it with the crush collar. The crush collar's bend should face the tapered and threaded end of the pinion. Push it in and install the pinion yoke and then the washer and nut by hand. Hold the pinion gear with a rag and use the ½-inch air gun to run the nut on just enough that there is just a small amount of in and out play.
Lay the carrier down and remove the bolts around the circumference with the ½-inch air gun and correct socket. Tap it off with the hammer. Lay the new ring face down and put the carrier in the middle of the ring. Lift the ring and start the bolts by hand. Tighten all the bolts securely.
Put the bearing races on both sides and hold the right shims on both sides of the bearing races. Lift the whole unit up and insert it into the housing. Make sure the races are straight and the shims are sliding in. If necessary, gently tap the shims in with a hammer. Do not hit them too hard or they will break. If they do not slide in, rotate the carrier a little and try again.
Install the carrier clamps and bolts and tighten with the ½-inch air gun and socket. Rotate the carrier so that the center pin can again be removed.
Tighten the pinion nut in increments until there is no in-and-out movement and only 20 to 25 degrees of freeplay in the pinion yoke from left to right. Remove the lock bolt and center pin in the carrier. Push the axles all the way in on both sides and install the c-clips one at a time. As a c-clip is installed, pull that axle out again to lock the c-clip in the axle. When both are in, insert the center pin and lock bolt and tighten.
Clean the cover with brake clean and let it dry. Put an 1/8-inch bead of RTV silicone all the way around the cover and let set for five minutes. Install and tighten the bolts with the 13mm socket. Open the filler cap on the side of the housing and add the positraction additive, then fill with gear oil. Install the remaining components in reverse order of removal.
