Ring and Pinion Install

This was the 3rd time I needed differential work, and figured it was about time I learned how to do it. The first thing I needed was a good reference manual. I bought a factory service manual from the dealer hoping it would be some help, and it was. It has very good detailed procedures that are easy to follow. I read the procedures a few times making sure I understood every step, and figured out what tools and parts I needed. According to the manual, there is a "special tool" for just about everything, but some aren't needed and most can be made. Below is a list of the parts and tools I needed, and what they cost me.

I initially had 3.07 gears with a lock right in the back and an ARB in the front. I was installing a 2.5" lift and wanted at least 31" tires. I went with 3.55 gears because I would have needed a new ARB in the front for gears any lower. In the rear, I just needed a new open carrier for the lock right. I didn't change any of the pinion/carrier bearings because the jeep only had 55K miles, but I did put in all new seals. Putting in all new bearings front and rear would probably add another $200. The following is the ring and pinion ratios for the high and low carriers (for YJ's).

Most of the stuff I made wasn't too hard, but I do have an arc welder, and access to the machine shop at work. I needed to use a lathe to make the tube to press on the pinion bearings, and to make the plug for the end of the carrier. The plug goes into the end of the carrier, so the puller has something to push on while pulling off the bearings. The press isn't absolutely needed, but it makes installing bearings very easy. The case spreader also isn't absolutely needed, but makes it easier to get the carrier in and out. The bearing puller is needed to pull the carrier and pinion bearings. The manual used a special bearing puller, where I used a standard bearing separator and fabricated puller. The yoke holder is something you cannot do without. With the housing sitting on the bench, you need something to hold the yoke while tightening the pinion nut. A large plumbers wrench and pipe would also work.

I started with the 35C rearend. The case spreader was not needed to get the carrier out. I used 2 large screw drivers to pry it, and it popped right out. I thought the pinion would fall right out, but I had to tap on it lightly to get it out. When putting in the new pinion, I didn't have to change the pinion height shims because the offset on both pinions was 0. There is a number scribed into the end of the pinion which is the offset from the perfect pinion height. So to get the pinion height correct, just take the difference between the old pinion and new pinion and adjust the shims.

The 35C has a crush washer for pinion bearing preload. To get the preload correct, you tighten the pinion nut until it takes about 15 inch/lbs to rotate the pinion(if using new bearings, it is a little higher). So I had to go back and forth tightening the pinion nut alittle, and measuring the torque to turn the pinion until the torque was within spec.

After the pinion was in, I needed to determine the carrier shims. One nice thing about the 35C, the carrier shims are on the outside of the carrier bearings, so you don't have to remove bearings to adjust the shims. The procedure is to install the carrier with bearings installed (no ring gear), and shims for a starting point on each side. The manual says to start with .080 thick shims on each side, but the shim set I bought only went down to about .140, so I used the 2 thinnest ones. Now the dial indicator is used to measure the total play side to side to determine how much shim to add to each side. I did this, adjusted the shims(also adding .004 to each side for preload), then installed the ring gear. Then I measured the backlash with the dial indicator and it was .004. The spec is .005 to .010, so I adjusted shims and got it to .006. The last step is to check the gear pattern, I used prussian blue marking compound. The pattern shows if the backlash and pinion height is correct. It wasn't real easy to get a good readable pattern, but I was satisfied with what I got.

Now for the front model 30. To remove the carrier, I had to use the case spreader. I tryed prying it out, but it was pretty tight. I spread the case .010, and the carrier came right out. I then removed the pinion and pulled the bearing. Now it was time to replace the seals. There is 1 seal in the tube next to the carrier, and 1 on the outboard side of the axle disconnect. Both seals were easy to remove with a long metal rod. I used a large socket to tap in the seal next to the carrier. The axle disconnect seal was a PITA because of its location. There is a special tool for this, and would have saved me some time. I finally got it in by grinding a piece of metal the same OD as the seal, and then taping it in with a long metal rod.

The new pinion had a different offset than the old pinion, so I had to adjust the pinion shims accordingly. On the 35C, the pinion shims were under the inner pinion bearing, but on the 30, they are under the inner bearing race, so I knocked out the race, and adjusted the shims. The 30 uses shims for pinion preload (instead of a crush washer like the 35C), and I decided to try and use the same shims. I installed the pinion, bearings and shims, and tightened the pinion nut to about 200 ft/lbs. To see if the preload was correct, I measured the torque(in/lbs) to turn the pinion, and it was in spec.. If it wasn't, I would have had to remove the pinion, adjust the shims and remeasure.

The next step was to install the carrier and adjust carrier shims. Because I was using the same carrier and bearings, I installed the new ring gear with the original carrier shims. This way, I wouldn't have to pull the bearings on the carrier. The backlash was right on at .007. The standard procedure is to install the carrier without any shims under the bearings and no ring gear, then measure the total movement side to side using the dial indicator. Then you would install the ring gear and measure the play between the ring and pinion to determine the ring gear side shims. The other side shims is the total play minus the ring gear side play plus .015 for preload. When it was all done, I checked the gear pattern, and it looked good.

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