Removal of the differential case reveals one key advantage of some Chrysler axles. Instead of using shims to hold the differential side bearings in place, the Chrysler 9 1/4" axle makes use of threaded adjustment spacers. Movement of the spacers requires either painstaking movement using a probe through a small opening, or a special tool. Wes Mohr had made his own tool. It's basically a specially shaped nut which must be placed on the end of a long shaft.

The shaft is inserted along the axle housing and the special nut fits into the spacer. The spacer is rotated either direction to force the side bearings inboard or outboard. For removing the differential, both spacers are pulled outboard. The advantage which arises later is that backlash can be adjusted by rotating these spacers, instead of by using side bearing shims.

Once the side bearing spacers are pulled back, the differential, along with its side bearings, can be pulled straight back out of the axle housing. In this case, since I neglected to purchase replacements, the ring bolts were removed even though the existing open differential was not to be reused.

Step 4: Remove the Pinion

The pinion is held in place by front and rear bearings, shims, and a crush washer while bolted to the driveshaft yoke. The pinion can be removed by removing the nut which holds it to the yoke. The pinion can then be forced back through the axle housing, and the bearing races can then be forced out.

Step 5: Preparing the New Differential

Ideally, the new differential (in this case, an Auburn LSD) is prepared by heating the new ring gear to 300 degrees farenheit. It is then mounted to the new differential case using twelve new ring bolts (which are reverse threaded). In this case, the existing bolts were used to mount the ring gear, without heat treatment (heat treatment would likely have removed the setup markings on the ring gear). Also, the ring bolts were not properly tightened in a crossing pattern. Unfortunately, many mechanics play fast and loose with impact wrenches. Having already imposed pretty significantly to take pictures for this article, I was reluctant to stop work to explain the importance of proper application of torque. If hiring a shop to rebuild a differential, you may want to personally oversee the work or discuss it with them beforehand if you want the work done properly. However, as annoying as corner cutting can be, it is seldom fatal to a project.

After preparing the differential, the pinion must be prepared. It is advisable to first put on only shims and the rear bearing until the desired setup is achieved.

Step 6: Differential Setup

Differential setup involves adjusting the side and pinion bearings to produce the correct contact pattern between the pinion and ring gears. An incorrect pattern produces irregular wear on the gears and applies excess stress to the bearings. Setup must be done correctly, or irreparable harm will likely be done to the components before it can be re-set.

Differential setup can be described by dial indicator measurements from fixed reference points. However, in practice, it is best described by matching the contact pattern with that set at the factory for a matched ring and pinion set. US Gear marks both the numerical measurements as well as the contact pattern on the gear set. The contact pattern is shown with yellow paint. During setup, viscous blue liquid is brushed onto the ring gear and the ring and pinion are meshed, turning against some resistance in both directions (drive and coast). This motion produces a contact pattern in the blue on both the coast and drive sides of the ring gear. Comparison to standard photographs indicates whether the backlash needs to be increased or decreased to correct the pattern. When the pattern provided by the manufacturer matches that obtained with the blue, the setup is finished, and can be counted on to last.

The adjustment of backlash is accomplished on the Chrysler 9 1/4" axle by adjusting the side bearing spacers. The backlash must be kept to within 8 to 10 thousandths of an inch while adjusting the contact pattern. Adding or removing shims between the pinion rear bearing and the pinion gear adjusts the contact pattern. The differential and pinion are assembled and the backlash is measured and the wear pattern is checked. If the wear pattern and backlash aren't acceptable, the differential and pinion are disassembled, shims are added or removed and the spacers moved, and the setup is checked again. This process is repeated until the setup is acceptable.

   

       

Once the setup is acceptable, the pinion is fully assembled, with the front bearing and crush washer, and the yoke is tightened into place.

Step 7: Installation of New Wheel Bearings

Odds are, unless they were recently replaced, that your wheel bearings and seals could stand replacement. The bearings and seals are easily pulled with an appropriate tool. New bearings and seals can then be pressed into place. These wheel bearings are lubricated with the gear lube.

Step 8: Installation of New Axle Shafts

Unless new lug bolts are being used, the old lug bolts must be pounded out of the old axle shafts and into the new shafts. Then, the shafts slide through the axle housing and in through the differential side bearings, with the splines lining up. Again, the set bolt and the center shaft must be removed from the differential to allow each axle in turn to move slightly inboard. Each C clip then slides easily back into place, and the differential case shaft and set bolt are replaced.

Step 9: Completion

With the new axle shafts in place, the differential cover can be replaced with a bead of permatex. It is important to remember that a modifier must be added to gear lube when a limited slip differential is used. Finally, the wheels are replaced and torqued. In this case, I did manage to hold back Dave with his impact wrench. I've had an aluminum wheel tear off my Ramcharger with my wife driving, and I highly recommend that anyone with aluminum wheels keep close tabs on the torque on their lug nuts. I've also had a bear of a time removing lug nuts after some joker with an impact wrench all but welded them to my lug bolts. Finally, the rear drive shaft can be bolted back into place. The standard Ramcharger setup uses bands.

In my case, I changed my gear ratio in the rear axle, but not the front ratio. The speedometer gear and the front ring and pinion will be swapped in phase II of this project. I'm the only one who drives my truck, so I'm not overly worried about having two different ratios in my truck temporarily. However, I would suggest removing the front drive shaft if you're going to have different ratios in place for any length of time.