Gear Swap
FOUR WHEEL DRIVE WEB
This is an overview of my gear swap. I will try break down the install in easy to follow steps. I will also discuss the problems I had during the install and how I solved them. At this point I have only done the AMC 20 rear end. I will add the Dana 30 after I have completed that install.
It took me several weeks to decide that I was competent enough to take on the challenge of installing my own gears and a Detroit Locker in my AMC 20 rear end. I arrived at this decision based on the following:
1. Installation of gears by a local shop costs between $600-$750
2. My Jeep isn't a daily driver so I can afford to have it sitting in my garage for a week if necessary.
3. I am a fairly competent shadetree mechanic and I have lots of tools.
4. I would rather work on my Jeep than pay someone else to.
5. The installation money I saved was enough to buy a Detroit SofLocker.
Gears
Once I decided to do the install myself I needed to purchase my gears and the Detroit. I looked through some catalogs and searched the Web for the best price and the most complete kit. I ended up buying my gears and Detroit from Drivetrain Direct. I got Spicer parts for the Dana 30 and Superior parts for the AMC 20. Their install kits include Timken bearings and all the necessary seals to do a complete overhaul of the differential. My only complaint was that they didn't provide any installation instructions. I was told by my salesman that detailed instructions would be included. I was able to overcome this with help from the Off-Road Jeep Forum and other websites listed below. If you really need instructions Randy's Ring and Pinion includes a complete instruction set with your gear purchase. The gears and locker with install kits and shipping were about $950 with the Detroit accounting for $480 of that amount.
Tools
Now that the gears were on their way I started gathering information about special tools that I did not have. Here is a list of the tools I used during the install.
1/2" drive socket set
Standard wrench set
Various hammers
Dial
indicator
Bearing
seperator
Bearing
press
Three foot long breaker bar
Impact
gun
Brake line wrench
Pry bars for removing the carrier case
Assorted punches
Oil drain pan
Foot pounds torque wrench
Inch
pounds torque wrench
6" Bench vise
I ended up spending about $150 on tools and various other items during the install.
Disassembly of AMC 20
Before the gears arrived I removed the rear axle and placed it on some sawhorses so it would be easy to work on. I removed the diff cover and drained the oil. I left the axle draining overnight to get as much out as possible. The next day I began disassembly. I lay some cardboard on a work bench so I could lay out the parts as I removed them and mark their original location with a pen on the cardboard. Remove the rear brakes and axle shafts. Disassembly of the differentials is fairly easy but it is very important to keep track of the shims and their original placement. You should also mark the location bearing caps. You may need to use a pry bar to remove the carrier from the case. The most difficult part of the the disassembly is removing the pinion and bearing races for the pinion bearings. To remove the pinion you must remove the yoke. Once the yoke has been removed re-install the pinion nut so that you can hit the pinion out with a heavy hammer. You will have to hit the pinion fairly hard to unseat the bearings. Once the pinion and pinion bearings are out you can remove the bearing races. I don't have a race puller so I use a punch to remove the races. I begin by lightly tapping the races as I move in a circular direction around them. As they start to come out you can hit them a little harder, if you hit them to hard they may get wedged in. A race puller would eliminate this step. Now you have an empty differential and you need to clean it. I used some degreaser and lots of rags. You should push rags through the axles to remove any oil or debris that may be present. Make sure everything is very clean, this will make it a lot more pleasant to work on and will eliminate the possibility of contaminating your new gear oil. When are those gears going to get here?
When the gears arrived I opened all of the boxes and checked to make sure I had all of the necessary installation parts. Everything was there except the mystery instructions I was promised. Lets start the install.
Installation for AMC 20
Since I used all new bearings and I had to get new carriers for the swap I really didn't have to do anything with the old carrier or ring and pinion. I did remove the pinion bearing so I could use it to check my pinion depth and other settings before finalizing the install. I used my bearing press and bearing seperator to remove the bearing from the old pinion. I honed out the inside of the old bearing so it would slip on and off my new pinion with ease. I used a drill with a piece of foam and sand paper wrapped around a 1/2" drill bit to make a crude hone. Wrap foam around an old drill bit or dowel and then wrap the foam with sand paper. Insert the foam/sand paper into the bearing and begin honing away. It took me about 20 minutes to get the bearing so that it would slip on and off my pinion easily. I also ground down the outside of the old bearing race so that it would slide in and out of the case easily. This is necessary because on the AMC 20 the pinion shims go between the race and the case. Since I had the axle upside down on my sawhorses the pinion and bearings were held in place by gravity. I pressed the new bearings onto the Detroit and slid it and the bearing races into the case. I used the original shims as my starting point for setting the backlash and checking the initial gear pattern. With the original shims installed I achieved a very good gear pattern. I ended up adding some shims behind the ring gear side bearings to decrease the backlash. To measure the backlash you will need to use your dial indicator. Place the indicator so that it is touching one of the teeth on the ring gear. You should get a reading by rotating the gear back and forth. I wanted to have as little backlash as possible because of the Detroit. Now that I have a good pattern and proper backlash I am ready to start finalizing the install. I pressed the new bearing onto the pinion and installed the new races in the case. You should oil the bearings before final installation. I slid the pinion with crush sleeve into position and installed the outer pinion bearing, pinion seal, yoke, and pinion nut. This is where I encountered my first problem. You must exert a significant amount of torque(300-400 ft/lbs.) on the pinion nut to seat the bearings and crush the crush sleeve. I wasn't able to keep the yoke from turning as I tried to tighten the pinion nut. I initially used an impact wrench but this did not generate the necessary torque. After a day of head scratching and polling many people I ended up putting the entire axle on my bench and placing the yoke in my bench vise. This worked and I was able to start tightening the nut to the point that the pinion bearing preload could be set. There is a fine line between proper preload and over tightening of the pinion nut. Once the bearings hit the races the preload increases very quickly, a quarter turn of the pinion nut can be too much. It is best to tighten the pinion nut very slowly and check the preload often. If you over-tighten the pinion nut you will have to remove the pinion and use a new crush sleeve. With the pinion installed and the preload set you can install the carrier(Detroit), shims and bearing caps. Reinstall the axle-shafts and brakes. Before installing the cover check to make sure everything operates smoothly and that there isn't any binding. I installed the cover with a cork gasket and some Permatex gasket sealer. Reinstall the axle assembly into the jeep and fill the diff with SAE 90 gear oil.
Summary
It took me about 3 days to do the install on my AMC 20. This included new brakes, a thorough cleaning and the installation of Moser 1-piece axles. I probably spent about 12 hrs on the actual installation with another 12 hrs on research, prep and tool purchases. I am fairly meticulous and I am also very patient. These are traits that can be very helpful for this type of project. Since I already have all of the tools and have done one axle, I expect to complete the Dana 30 swap in about 8 hrs. These directions are in no way complete. I have only highlighted the main points of the install. You will need a good shop manual and any other information you can gather. I recommend reading through all of your material several times before beginning this project. It will save you time and reduce the likelihood of mistakes during the install. Please feel free to e-mail me any questions. I would like to refine these instructions so that anyone can follow them. I will be adding a write-up on the Dana 30 when I complete that install.
Terms and Definitions
These are not exact definitions but rather they are meant to be a laymen's explanation.
Backlash- The amount of travel between the ring gear and the pinion gear before one begins engaging the other.
Pinion Bearing Preload- The pinion's resistance to turning caused by the friction between the bearings and their races.
Gear Pattern- The pattern visible in the gear marking compound used to adjust proper gear engagement.
These are all of the links I used during my install:
West Coast Differentials Very good instructions.
Ring and Pinion Installation Instructions
Differential Assembly Specifications
Ring and pinion install Another Do it yourself page.
Randy's Ring & Pinion Tech Library
I also received invaluable suggestions and ideas from my friends at the Off-Road Jeep Forum.
