DANA 20 TRANSFERCASE
TWIN STICK SHIFTER CONVERSION
The purpose of this article is to serve as a guideline in converting the Dana 20 transfer case from a single shifter to a twin stick shifter. The modifications outlined here were done to the D20 from an Early Bronco (EB). The author is as yet unsure as to whether all aspects of this conversion will apply to the similar Jeep D20 xfer case. Inasmuch, the standard disclaimer applies.
The reader assumes all responsibility in performing the operations outlined herein. This document is meant to serve only as a guideline, and cannot be guaranteed to provide complete information in every circumstance. As every 4x4 project is different, it is up to the reader to determine if the project, and any unforeseen complications that may arise, are within his or her ability to deal with, and improvise solutions to. It is also strongly recommended that you read this article in its entirety before beginning, to familiarize yourself with the procedures and tools involved. I did this conversion myself with no outside help, only my wits, so if you’re mechanically inclined this shouldn’t be too hard. However, you just never know, so if you screw something up, I don’t want to hear about it. To summarize: Proceed at your own risk.
At this point you should have decided whether to tackle this project yourself, or give a copy of this tech article and your checkbook to your local 4x4 shop to perform the modification for you. I’m assuming you’re going to do this yourself, so I’m writing this with more basic tools in mind, and I’ll explain some of the stuff more in depth. If it gets a bit wordy, just skip ahead, as others may need the extra info.
First of all, you need to put together a mental inventory of what you’re going to need. Foremost, you need a good place to work on your rig. If you can do it outside, more power to you, but I would recommend at least a garage, preferably with a concrete floor. I bribed my 4x4 club president (and good friend) Tye Jones (CJ5Driver) into letting me use his garage by buying him pizza. Next, you’re going to need basic hand tools to remove the transmission and xfer case (as well as a set of allen wrenches with the “universal joint” type ball end and at least a hacksaw), a jack or a buddy to help you lower the unit to the ground, a pair of shifters (or something you’re going to turn into shifters), and hardware to attach the shifters to a solid location and to the shift rails. A shop manual is also very handy. In addition, you may also need an acetylene torch to free up stubborn bolts, a welder if you plan to get fancy with brackets, most likely a drill and [sharp] bits, a long slender magnet or magnetized screwdriver would be helpful, and probably a case of beer. Oh, and put the nearest Papa John’s Pizza on speed dial. (Don’t forget to tip well, as you’ll probably be seeing the delivery guy several times during this project). Lastly, you’re going to need some downtime for your rig. It’s best to have a second vehicle, because it sucks having to walk to AutoZone halfway through the project.
Personally, I found it easier to figure out what I needed after I had the trans/xfercase unit removed. This is where your buddy, jack, and the beer come into play. I decided to remove everything as one unit. After unbolting the trans from the bellhousing, and removing the crossmemeber, my buddy Tye and I lowered the extremely heavy unit using his “Big Bertha” floor jack. Do not drop it on yourself. It’s heavy, and you don’t have enough beer for that kind of pain.
Once it’s out, start playing with the transfer case shifter, and learn how and why it works. When you move the lever, it’s connected to a link that moves a “transfer bar”. This xfer bar in turn moves the shift rails. The shift rail on the left (driver’s side) shifts the front axle output. The shift rail on the right shifts the rear axle output. Notice how one rail always moves first? This is because of the interlock pins. There is an internal mechanism that prevents the front axle shift rail from moving out of neutral until the rear axle shift rail has been engaged in a gear other than neutral. Notice that the reverse is also true: the front axle goes to neutral before the rear axle. You will also want to note the location of the shifter in relation to the ‘case, as this will help you in enlarging the shifter hole in your floorboard later on if you’re doing t
his on an EB.
Having studied the operation of the shifter, you can get an idea of what we’re going to do. Since each shift rail controls the shifting of either the front or rear axle, you’re going to remove that link rod and the transfer bar, and then set up two shifters so that each shifter shifts a separate shift rail. Seeing this, you should look for a mounting location for your shifters.
On the EB, the stock shifter pivots on a bolt that threads into the intermediate adaptor housing. I decided that since I had a spare stock shifter, I was going to make it look similar to stock. I also decided to use a similar method of mounting it, where I would simply replace the stock pivot bolt with a lo
nger one and have both shifters on it (If you decide to fabricate your own shifters, your mounting method will vary). However, I have seen some adaptor housings where the bolt was nutted on, and the housing was not threaded. In this case, you’ll have to come up with a slightly different mounting method.
Next, I went out to the hardware store with the stock pivot bolt and shifter in hand. I found a bolt that was the same diameter and thread pitch as the original, only longer so both shifters would fit. Now I had to find a way that I could tighten the bolt without tightening the shifters against each other, causing them to bind. I got some bronze bushings with an inside diameter the same as the bolt diameter. I got enough of them (they were about an inch long) so that they were as long as the bolt’s overall length. You could substitute pipe of the correct diameter also. Then, using the bolt, bronze “sleeves”, and shifter, I found a couple of plastic bushings that would make for a snug fit between the sleeves and the shifter. Besides a shifter boot, these were the only parts I had to actually buy.
MOCK ASSEMBLY AND INITIAL MODIFICATION
Back at the ranch, it came time to roughly assemble the parts tog
ether. Sliding the two shifters onto the new pivot bolt, it became clear that they would be spaced very widely apart, and would probably not fit without considerable floorboard trimming. So what I did was cut down the “pipe” that was welded into the shifters as a pivot so that they would be closer together (set to my liking). Note: If you’re not sure, you may want to “mock-up” your shifters before cutting, as described a paragraph or two below, to get an idea of what needs to be cut.
With the shifters trimmed, it’s time to do a bit of measuring. Lay the shifters on the floor in positions relative to how they’ll be installed. Now, you need to get the proper length of “sleeves” so that you can tighten the pivot bolt properly, and not tighten the shifters causing them to bind. I put the sleeves on the bolt, and then set it next to the shifter’s “pipe” pivot. I marked the sleeve on the end of the bolt, so that I could cut it down. The idea was to have the sleeves just slightly longer than the “pivot pipe” on the shifters. This way, the bolt would tighten against the sleeve, and allow it to be cinched down, while the shifters would still have a slight amount of side-to-side looseness to alleviate friction.
Once the sleeve(s) was cut to length, I was able to assemble the shifters on the adaptor housing in a mock-up. Now it’s possible to see how things are going to line up. Since you basically want the bottom tab of each shift lever to line up with the shift rails, you may need to do some bending. This is where the torch is your friend. Heat and bend the shifter’s lower sections until it meets your liking. Just make sure the plastic bushings are don’t get near hot metal unless you want to go back to the hardware store.
Now you need to fabricate a way to attach the shifters to the shift rails. What I did was fabricate new “link rods” using the original link rod and transfer bar. On one shifter, I put the original link rod back in, and cotter pinned it in place. Then I enlarged the hole in the corresponding shift rail so that it was as large as the “tit” on the link rod. Lastly, I heated and bent the link rod until it would inse
rt into the shift rail where I cotter pinned it in place. On the other side, I used a similar method. I welded up the “slot” on the end of the xfer bar, and drilled out a hole for a bolt. That end I bolted to the shifter. Then, I twisted the bar until it was parallel with the slot in its corresponding shift rail. Insert, and bolt into place. Rejoice! Now both your shifters should be able to shift the xfer case! (You
might eventually want to put some bushings in there if the shifters are loose or sloppy).
Your tcase is now twin-sticked. You now have the ability to go out and enjoy the fun of a twin stick shifter. However, if you want to gain additional drive ranges (front wheel drive, and rear wheel low), you need to proceed on to the next section. If you hare happy with the setup as it is, or feel you do not have the skills to complete the next section (if you did the first part, you most certainly do have the skills!), then you can safely operate your twin stick as is. Otherwise, proceed to the next section.
author: By Ryan Bell (AKA: 69Bronco)