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All things considered, the Dana 300 transfer case is an excellent choice for the off-roader. It has a strong cast iron case and a decent 2.62:1 low range, which is considerably better than the 2.03:1 in the Dana 20 I'm replacing. In addition, the Dana 300 is also plentiful, since there was one put in almost every Jeep CJ built from 1980 to 1986. It can be "twin-sticked" relatively easily with available aftermarket kits and even lower gears are available from several sources. The main problem is that the 300 hangs down more than the 20. That's where the new Dana 300 Rotation Kit from Advance Adapters comes in. It allows the Dana 300 transfer case to be rotated counter-clockwise to four positions (prior to publication Advance Adapters added two more positions to the adapter pictured in this article for even more versatility). How far you go depends on your vehicle and your willingness to make needed modifications resulting from changing driveline angles, reduced clearance under the body, etc. With the right combination of body lift, transmission clearance, exhaust system, driveshaft angles, etc., the rotation kit could allow the use of a skid plate that is virtually flat across the bottom of the frame. The kits (Dana 300 Rotation Kit and the Dana 20 to Dana 300 Conversion Kit) come with almost everything you need, with the exception of RTV sealer and a good thread-locking compound. The transmission to transfer case adapter includes the adapter, new output shaft, rear seal and snap ring, and necessary seals, gaskets and bolts. While it's not the intention of this article to go into detail on this part of my swap, I will point out a few possibly obvious points. First, read the instructions thoroughly, and follow them! They are well-written and will save you time in the long run. Second, if you have a Jeep T-18 transmission like mine, you will need to drill two holes in the case, as the adapter mounts differently than the Dana 20 adapter did. Get some help here, both while marking hole location and in the drilling process. If you have access to a drill press large enough to hold the trans case in a vertical position, use it. Third, if you don't know how to completely disassemble your transmission (and reassemble it), this part of the swap is not for you! On the other hand, installation of the rotation kit itself is much easier to install. If you can remove the transfer case and perform relatively minor disassembly, you can do this. The Rotation kit includes the adapter ring, longer transfer case input shaft, a sealed input shaft bearing, gasket and new bolts. Prior to removing the skidplate, use a jack stand to prop up the transmission at its normal height. This will help in determining rotation later on. Also, be on the safe side and engage your parking brake and chock your wheels. Once the transfer case is removed, you must remove the input assembly to install the new input shaft. Remove the six Allen head bolts and use the two grooves in the aluminum front bearing retainer to carefully pry out the assembly. An extra pair of hands definitely helps here. Once you have the retainer removed, remove the two snap rings and take the assembly apart, noting the position of each part. Replace the input shaft and bearings with the ones provided in the kit (the sealed bearing isolates the gearbox fluids). Install the snap rings, line up the 6 counter sunk holes, and reinstall the retainer assembly back into the case. Use RTV to seal the retainer to the case and thread-locking compound on the bolts. Torque the bolts to your vehicle's specifications using a criss-cross pattern so that the retainer is sucked down evenly. Once the retainer is installed, you must decide on how much you are going to rotate your transfer case. If you positioned your transmission at its normal height as previously suggested, you can mount the t-case (without gasket or sealer and shifter assembly), and rotate to the best position for your application. A suggestion here is to use a small pin punch on the outside of the adapter to mark the location of different locating holes. Place these marks where you'll be able to see them when the t-case is installed. Advance Adapters advertises rotation to 2 or 10 degrees, but they are referring to rotation from an absolutely level position, not rotation from stock position. The latest version of the rotation adapter, with it's 2 additional location holes, will allow even further rotation, assuming proper clearance at the transmission, body, etc. In my case, to utilize the first locating hole in the adapter ring, (which would be the second in the new version) I had to grind material off the right, rear, upper corner of the transmission case and the inside of the shifter mounting portion of the aluminum front output bearing retainer. This gave me enough clearance to rotate my t-case almost 20 degrees. I also "twin-sticked" the t-case using shift levers from a Spicer 18 t-case. To mount the shifters, I had to file down the insides of the mount to the proper width, and drill out the shifters to accept a 5/8" bolt. I also ground a groove in that bolt to accept a set screw that was drilled and tapped into the housing. At the bottom of the shifters, I drilled a 1/4" hole to allow them to be connected to the shift rails. After some trial and error, I used two short pieces of 1/8" flat 1/2" wide steel, twisted 180 degrees, to bolt to the shifters on one end and the shift rails on the other. So far this has worked perfectly. If you want to skip this step, I suggest you contact Currie Enterprises and have them send you a twin stick conversion kit and shifter boot. Either way, if you choose to do this modification, you will need to disassemble the t-case and remove the shift interlock "pills" to allow the shift rails to work independently of each other. You will also need to bend both t-case shifters to the right to correct for the amount of rotation. You can see by the photo that I was able to gain just over 3" of additional clearance by rotating the transfer case. This placed the t-case at an almost level position. Once you've installed the case, fabrication of your new cross-member/skidplate can begin. To gain the most clearance possible I fashioned a much shorter mount from the original metal "outrigger" plate and a piece of 3/4" thick hard rubber. from a scrap piece of matting used to cushion the weight room floor of my local health club.
You can use the original mount of a polyurethane version, but it is almost 2" high, and would result in a lower skidplate or designing a different mount, altogether. In the next photo above you can see a comparison of 3 skidplates. My customone, in front, hangs down only 2 3/4" from the frame. The Dana 300 factory plate in the middle hangs down over 5 1/4", and the Dana 20 factory plate in back hangs down 4 1/2". This means that I have increased my over-center clearance by 2 1/2" ! And, with the exception of my traction bar mount, which was previously mounted to a separate crossmember, the skidplate is completely flat!
The level of oil to fill the transfer case with after rotation will change, since the fill plug is rotated considerably higher than stock. In my case, I removed the top left bolt from the cover at the rear of the front output shaft and used that as my level indicator, since it was approximately the same height as the fill plug was originally. So, was it worth the time and expense? Your application may be different, but let's think about this. To get that 2 1/2", you would have to install a taller suspension lift or 5" taller tires. Sure, these would increase differential ground clearance, but they would also greatly increase your vehicle's center of gravity as well. For me, after rolling my previous CJ-7, with 7" of suspension lift and a 2" body lift and 38 1/2" tires, the answer is obvious. With 35's, 6" of suspension lift, and no body lift, with proper tire placement, I can go pretty much the same places I used to go. You decide!
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