Introduction:
I have a stock 88 Jeep Cherokee Chief that has provided me with many miles of off-road driving pleasure both in the desserts of California and in the Mountains of Colorado. This winter, I decided to upgrade my Jeep and make it a better rock crawler. After doing some engine and suspension work, I turned to the stock open differentials. I spent about a month learning how every aftermarket differential works and corresponding with scores of people on the internet about their real world experiences with various types of aftermarket differentials.

I came up with the following conclusions: 1) ARB was the best choice for a vehicle that is driven regularly on the street, but I couldn't afford one ($650 + $200 for the compressor). 2) A Lock-Rite or Easy Locker was an effective solution for the rear, but I didn't want to sacrifice street performance (Mis-behaves around corners and in parking lots). 3) A Trac-Loc was a definite improvement over stock, was inexpensive, and would not compromise my every day driveability. I chose the Trac-Loc and have been very happy with the results thus far. The unit cost me about $200 dollars plus $5 shipping from Ring and Pinion service.

Let me say that I had never opened up the cover on any differential before I did this job. Some research and the factory service manual completely prepared me and I wouldn't hesistate to recommend any able backyard mechanic tackle this him or her self.

The Vehicle:
The installation was performed on a 1988 Jeep Cherokee Chief. The Jeep had 140k miles on it, runs great, and has seen at least 10,000 miles of rough trails, rocks, streams, dirt roads, ecetera. The XJ is completely stock with the exception of 235x70 Pathfinder radials and some nice looking rims that the previous owner had installed. I bought it about 4 years ago with 90k miles on it. The XJ is one of the most versatile vehicle that I have ever owned (18 vehicles and counting) and I don't plan on selling it anytime soon.

Special Tools Needed:
Dial Guage (I had a small 0.0005" per div unit) Caliper (I had a Mitutoyo accurate to 0.0005" which was way overkill) Factory Service manual (not required but very helpful) That's it.

Removal of old carrier:
This was really easy. I jacked up the Jeep and placed a jack stand on each side about where the front of the leaf spring attaches to the body. This allowed the rear axle to droop all of the way down and give me the max working room. Removed the wheels and pulled off the rear drums. Removing the drums turned out to require a large pulley puller. I don't know if other jeeps are like this, but my drums were not removeable by hand and required quite a bit of force to get off. Lucky that I had the puller handy. I then removed the four teeny flimsy looking bolts that are in the brake drum area (It's really scary that these things hold the axle in) and pulled out the axle shaft by hand (no slap hammer required). I was really surprised at how weak the retainer plate and bolts looked. Pulled out each axle about 6 inches.

The hardest part of the whole job was removing the differential cover. The cover was RTV'd in place when the Jeep was made and I tried everything from screwdrivers to chisels to a razor blade to get between the cover and the differential (after removing the bolts of course). Finally, I did it with an old serragated steak knife and a hammer. I pried the cover loose and let the oil drain into a pan.

Decided to measure backlash and record gear pattern before removing the thing for later comparison. I hooked up my dial indicator to the case with one of the cover bolts (fit just right) and rocked the carrier back and forth to measure backlash. I put the indicator tip on the outside of the drive side of the ring gear. It lined up pretty good but not perfectly. I was worried that it would be hard to move the carrier to measure backlash without turning the pinion and corrupting the measurement. It turns out that it's easy to tell what the backlash actually is and when you run into the pinion. I got a measurement of 0.012" backlash (spec is 0.005" to 0.009"). Like I said, the measurement might have been a little off since I didn't get the guage lined up perfectly. I also coated some ring teeth with yellow ferrous oxide (gear marking compound) and recorded the contact pattern. The pattern was perfect, just like in the books.

I marked the differential carrier caps (much like main bearing caps) with a point shaped cold chisel so that I would be sure to put them back later on the correct sides with the correct orientation. I simply tapped a little mark into the upper outside area of each cap. Didn't have to worry about them getting mixed up after that since all that I had to do was make sure that the little marks were on the outside and at the top. I loosened the bolts about 3/8" out and then gave the carrier a good pull with my hands. Lucky that I left the caps on or I would have dropped the thing right onto the ground. The carrier came loose easily (the Jeep has 150k on this carrier). I removed the bolts and stuck them into a piece of cardboard in the correct orientation (so that I would not mix the locations up for re-install). pulled the carrier the rest of the way out.

Brought the carrier to my work bench and loosened the eight bolts that attach it to the ring gear. The factory service manual (very helpful by the way) says to use a brass punch to tap the ring gear off. I don't have a large brass punch so I just loosened the bolts a bit and pounded on them with a hammer until the ring gear had moved down a bit. I then loosened the bolts a bit more, pounded more, etc. The ring came off nicely and I have confidence that I didn't damage the threads by removing it in the manner that I did.

I had new Timken bearings to put on so I didn't have to remove the old ones from the existing carrier. I think that If I did have to remove the old bearings, I would have taken it to a machine shop to get it done. I installed the new bearings onto the new carrier with a rubber hammer. Not as neat as a press but they got on there without any galling. I had to improvise with my vise to get the bearings on the last 1/8" because the carrier shaft sticks out beyond the bearing. I opened the jaws of a vice enough to allow passage of the carrier "shaft" but not the bearing. This way seemed to work well and the bearings looked very good in the end. In retrospect, I might have been well advised to have a shop press them in for a few dollars.

I bolted the ring gear on with NEW bolts that were supplied with the carrier from Ring and Pinion Service and proceeded to install the unit. By the way, Ring and Pinion was very helpful and good to deal with. I recommend them over Reider Racing.

INSTALLATION:
I thought that I would try to install the carrier with the original shims as a starting point. The shims go in the outside on the carrier unit and were easy to switch (e.g. didn't have to remove any bearings). I was not able to get the new carrier in at all with the original shims. I then selected shims that were 0.004" smaller than the original ones on each side (used my caliper to measure all of the shims from the shim kit in advance and set them in order on the work bench). I still couldn't get the carrier in so I went another 0.004" smaller on each side. The carrier went in easily with this combination. I could not detect any back and forth play in the carrier at this point.

I installed the caps and measured the backlash and found it to be about 0.010". I removed the unit and selected shims that were 0.004" bigger on the left (drivers) side and 0.002" smaller on the right side. This would move the carrier 0.002" closer to the ring gear decreasing backlash) I had to tap the shims in with a hammer to get the carrier in with this combo (read: created some preload). I bolted the caps back on and measured backlash which was 0.008". Eight thou. is in spec so I stopped there.

I then coated a few teeth with gear marking compound and spun the carrier around a few times. Looked at the contact pattern and though that it was pretty good. It's really a little hard to tell where the gears are hitting by using the compound. I think that a brush with really fine bristles would work better than the one that I had. By the way, Ring and Pinion service provided the compound and a brush for free without me asking. Checked the backlash one more time and found it to be 0.010" Decided that 0.001" out of spec was good enough since it was better than the working combo that I took out. Coated the cover with RTV, bolted it up, and poured in new lube and friction modifier.

I have driven about 350 miles since with no whining from the rear end at all. I'm going on a short rock climbing trip tomorrow to see if I can break it. I really can notice the difference between this carrier and the open carrier. I found a spot in a parking lot where there was a patch of hard clear ice that had not yet melted. I positioned my XJ so that one rear tire was on the ice and the other was on dry pavement. Hit the gas and went like crazy. The wheel on the ice did spin, but the wheel on the pavement had plenty of traction. I had done this same test right before the installation and the Jeep just sat still while the wheel on the ice spun and spun. I think that a locker will happen in a few years when the car isn't my daily driver anymore. Also, I have high hopes that the "command locker" will come out some day and I'll put one of those in the front. I really recommend the factory service manual for anyone who works on thier Jeep. The factory manual tells you EVERYTHING down to the color and location of every bolt and wire.