DANA 20 TRANSFERCASE

TWIN STICK SHIFTER CONVERSION

DISCLAIMER

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.

PART 2

Getting Fancy with Interlocks

Shift Rail Removal

Removing the Interlock Pins

Reassembly

GETTING FANCY WITH INTERLOCKS

Now that you have your shifters hooked up you will notice that you are unable to shift the front axle (left shifter) out of neutral until the rear axle (right shifter) is in gear. This is due to the interlock pins, which allow a single stick shifter to function properly. However, when you twin stick your ‘case, they also prevent you from using other gear combinations. By removing the pins, you will gain front wheel drive, as well as rear-wheel low, two very useful off-road gear selections. On the flip side, if you simply remove the pins, it becomes possible to shift one axle into high, and the other into low. This will cause terrible binding and stress on the front and rear drive train, and if driven more than a few feet, or a few miles per hour in a high/low configuration, it could very easily damage axles, universal joints, drive shafts, or even the transfer case itself.

There is one solution that gets the best of both worlds: modifying the shift rails by grinding them, then re-inserting the interlock pins. Since this is a complicated operation that I have not performed myself (yet), you will have to figure this out for yourself. There was a previous write up in Peterson’s 4 Wheel and Off road magazine that explained a nearly identical operation on an NP205 Transfer case. It would be a valuable reference in tacking such a project. Alternatively, you could remove the shifter rails and pins as described below, and imagine how they interact, and how you’d have to re-grind the shift rail detents to allow it to function properly. As is though, I will tell you how to simply remove the pins. You just have to be careful when you shift so as to avoid a high/low situation, that’s all.

For this process, you are going to need a set of allen wrenches with the ball-socket on one end. Otherwise, the only way to remove the shift rails is to completely disassemble the entire ‘case, as the set screw that hold the shift forks to the shift rails are behind the reduction gears and require an “angle” on the wrench. This will be evident once the inspection plate has been removed, and the shift rails are visible. If you don’t have this type of allen wrench, I would recommend either using a shop manual for disassembly (as there are several small parts and bearings) or take it to a transmission shop.

SHIFT RAIL REMOVAL

In order to remove the interlock pins, you will first have to remove the shift rails. For this process you will need to remove your shifters and linkage fabricated in the previous section. Next you will want to drain the tcase of its oil, and remove the inspection plate on the bottom. Next, if you look at the raised metal boss that the passenger side (I think) shift rail slides in, there are two small bolts, about 7/16” or ½”. Remove these, and I believe there are a pair of ball bearings and springs that act as detents. Remove them also, and save them. A zip lock baggie or magnetic works well to keep these smaller parts from getting lost.

REMOVING THE INTERLOCK PINS

Now it’s time to get a little fancy. Flip the ‘case over and look past the gears at the top side. You are trying to locate the shift rails. (Wiggling the shift rails from outside the tcase can help identify them) Once you have spotted the shift rails, look for a small allen set screw that attaches the shift forks (the part that actually moves the gears) to the shift rails. Now that you have spotted the shift rails, you are going to remove the setscrew on the passenger side (as viewed from the top) shift rail. Don’t lose the setscrew; you will need it for reassembly.

Now you should be able to wiggle this shift rail loose, and remove it from the transfer case. The shift fork may drop off the gear it shifts, that’s OK. Just remember where it’s supposed to go. Now if you flip the ‘case back over, you should be able to insert your magnet into the hole where the 7/16” bolts came out of, and fish around until you can remove the interlock pins. Alternatively, you can tilt the case on its side and shake it until the pins fall out. The pins are about 1” to 1.5” long, are about ¼” in diameter, and have rounded ends. These can be set aside, although you should save them in case some day you want to convert back to a single stick shifter, or wish to

modify your shift rails as described earlier.

REASSEMBLY

Now all that remains is reassembly. Basically, you just reverse the above procedure. The only part that may prove difficult is getting the allen set screw to thread and line back up with it’s tapered hole in the shift rail. How I did that part was after inserting the shift rail back into the shift fork, I carefully worked the setscrew until it threaded. Next I had to get the setscrew to go into its tapered hole. I did this by very lightly tightening the set screw, and then moving the shift rail in the fork until I could “feel” the set screw start to go. This is where it helps to have a helper: one person wiggles the shift rail, while the other gives direction and maintains light torque on the setscrew. From there, you simply have to be sure the screw is tightened completely. This is done by a series of tighten-wiggle-tighten-wiggles, until the screw will no longer turn. This is important, because if it is not tightened all the way home, it could come loose and not only prevent shifting, but also cause major internal damage.

Once the case is reassembled with proper gasket sealant on the inspection cover, fill the case with the proper amount of SAE50 engine oil. (Others may use 90w gear oil, but the EB Dana 20 actually came with 50w oil from the factory). It is now time to install your freshly twin-sticked ‘case into your rig..