Slowing Down the Scrambler
Installing an NP435, Novak adapter to a Dana 300, Currie Twin Stick, and a Go2Guy TwisterBy Mo
Low gears. We all love them. They increase the torque output of our engines, allowing us to crawl over various obstacles with more precision and less wheel slippage. Less wheel slip means minimal environmental impact. Minimal environmental impact means one less thing the Anti-Acccess folks have to lie about to try to close our trails. (You can find more about Land Use issues here.)
I'm going to show you how I put together an excellent drivetrain from my Jeep Scrambler. This is a tried and true combination with a bit of a twist. The major components are a New Process 435 transmission and the Jeep version of the Dana 300 transfer case. This combination let me put a very stout transmission with a wonderfully low first gear (6.69:1) in front of the Dana 300 transfer case.
Special parts were acquired from Novak Adapters for the 435-300 adapter kit, Currie Enterprises for the twin stick shifters for the transfer case, and Go2Guy Engineering for their Twister.
Part 1: Installing the Novak NP435-Dana 300 adapter
The NP 435 transmission was produced for many years and used by all three major auto manufacturers, most heavily by Ford. This transmission features a 6.69:1 first gear ratio and a 1:1 4th gear. There are several versions of this transmission, but the easiest to use are the Ford versions. Ford used 2 different versions of this transmission: a 2wd and a 4wd version. The only real difference between these two is the bolt pattern for the tail section. The 2wd version has a square pattern to hold the tail housing, while the 4wd pattern looks like a trapezoid.
The Dana 300 transfer case is one of the more popular transfer cases in use, though not current in production, today. It has a good low range ratio of 2.62:1, gear drive and a cast iron case for strength. This transfer case also came in a few different configurations. The IH version of the Dana 300, produced only in 1980, is highly coveted as it is a bolt up replacement for a Dana 20 transfer case. The Jeep versions are much more common. They were in use from 1980 through 1986 and were available in all Jeep CJs. The first year it was in production, the Jeep Dana 300 is about an inch shorter than in later years. The two Jeep versions are bolt up replacements for each other, barring driveshaft differences. The Jeep and IH versions all share internals, but the Jeep and IH versions are not bolt compatible.
Both this transmission and transfer case are very suitable for living behind my low mileage AMC 360.
Mating the NP435 to the AMC engine is very easy. Using the stock bellhousing that came between a 258 and a T176 (or T150) transmission allowed me to do this for next to nothing. However, there is no stock adapter for the Dana 300 transfer case to the NP 435 transmission. Novak adapters to the rescue. They have been in the adapter business for a long time (since 1967) and this adapter is one of their premier kits.
Having the 4x version of the NP435, I needed to order Novak Adapters' kit #433-A4.
Here is what came in the box when I opened it. It looks pretty sparse, but really all you're going to do is replace the mainshaft and the tail housing. The tail housings of this adapter actually rotate the transfer case up a bit over the stock placement. This allows for increase ground clearance. The other parts are a new pilot bushing sized externally for the AMC crank and internally for the NP 435 input shaft. The o-ring is for the groove in the tailhousing (see the pic) and the bolt and washers went unused. More on this later.
Now you have to remove the input bearing retainer and the tail housing. Pretty easy. After removing the bolts, I used a rubber mallet to loosen the pieces from the tranny body. You'll need a decent size snap ring pliers to get the output bearing off, but the input shaft comes off pretty readily. Here is the case with everything removed that will be removed.
Here's the mainshaft and with the gears and various bits already removed. Another friendly hint: When you pull the gears off, keep them aligned when you lay them down and remember how you did it.
Here are the two shafts side-by-side. the new one is about 5" shorter. And that savings goes directly to driveshaft length.
Reassembly is exactly the opposite. Follow the directions, keep the gears in order, use grease liberally, tap lightly using a brass drift and a couple hours later, your NP435 will look something like this.
When putting the tail housing back on, the instructions call for using the supplied bolt and washers instead of the stock studs that were on my application. I saw no reason for this, so I called Novak and asked about it. I was not given a good reason why I couldn't just re-use the stud that was already there. Given that and the fact that with my luck, the bolt would have been long enough to cause interference with the gears inside the case, I chose to use the stud. So, I ended up with the proverbial "extra parts".
Here is the new pilot bushing installed. If you're converting an AMC engine from an auto tranny to manual, there will be a thin metal sleeve that needs to be removed from this same opening. I did this using big screwdriver and a hammer. I'm sure this isn't the recommended method, but it worked.
And here we are with it back in the rig. The skid is from an older CJ7 that had a T18/Dana 20 combo in it so the dropped part is a bit less, but you can still see I had to use a 2" chunk of aluminum to fit it up. I have a 1" body lift in there as well.
This kit does exactly what it is supposed to do. It mates a NP 435 transmission to the Dana 300 transfer case. There are a few things that you will need that are not included with the kit. However, Novak keeps them on hand so you can order them at the same time. I strongly suggest you order a new output bearing (I had to and it's completely removed as part of this install). I also recommend you order new input bearing retainer gasket as reusing a potentially 25 year old gasket is iffy at best. I got both of these from Novak directly, but I got the mount from Summit Racing as they are local to me. The mount, as seen in the last pic above, is an Energy Suspension part - it's a standard Chevy tranny mount. You should be able to get these at just about any parts shop in the country.
This is the first transmission job I've ever done. Not counting removal/installation of the transmission from the rig, disassembly took about 2 hours, reassembly took about 5 hours. I'm sure I wasted at least 2 hours on reassembly due to my bonehead move of not keeping the gears lined up properly.
Part 2: Go2Guy Engineering's Twister
Go2Guy Engineering is headed by Ken Blume. He runs in many of the rockcrawling competitions and knows his stuff. This is one of the first products offered by Go2Guy. Can't wait to see what else he offers.
The Twister basically is a 5/16" thick piece of steel. It is designed to be bolted to the Dana 300 (or New Process 231) transfer case and allows for three differing angles of rotation. You determine the setting you want to use based on the desired amount of twist you need. You determine this based on how much ground clearance you want balanced with how much space you have, or can make, underneath your rig.
This is a very complete setup. The Twister came finished in black paint which I manage to scratch up in short order. The Twister itself is a perfect fit around the mounting surface of the Dana 300 transfer case. The kit includes six flush mount bolts to mount the Twister to the transfer case itself. There are six studs with the associated nuts and bolts to attach the case to the transmission adapter. Also included is a sleeve that extends the transfer case input shaft sleeve. This piece was listed as optional and I did not use it. I hope I don't end up with extra 'rust inhibitor' splattered under my Jeep.
Here is the Twister with the studs installed in the first setting. Also pictured are the flush mount bolts used to attach the Twister to the transfer case.
So, let's get this thing installed.
I already had the transmission and transfer case out of the vehicle so I figured this addition would only add only take a nominal amount of time to complete. I was right. The installation added probably 30 minutes to my drivetrain installation. If the rig had been completely together, I'm going to guess it would take about an hour (assuming nothing goes wrong). I also want to note that I'm running a 1" body lift which I'm certain helped with this installation. As it was, I had to mildly massage a small portion of the body with my 2# 'persuader'.
First step is to make sure the Dana 300 mounting surface is clean.
Then you bolt the Twister to the it.
What I did next is install just one of the 6 studs. Ken told me that the typical NP435 to Dana 300 setting was the second setting, but knowing that the Novak adapter I was using already had a bit of rotation built in, I started in the first setting. I put the 300 in there, hand tightened the nut of the stud and checked the ground clearance. The bottom of the transfer case is just slightly higher than the frame. Bingo.
Pulled the transfer case back off, put a drop of blue Loctite (not included) on each of the 6 studs as I put them in the adapter. Put the transfer case back in the rig started to button it all up. I thought I had the case up against the adapter, but I didn't. Whoops. Oh well, nothing 10 minutes with a hacksaw couldn't fix. Thankfully, that ear isn't used by the Currie Twin Stick shifter.
In summary, this is an excellent product that is easy to install. To gain the full benefit of the new found ground clearance, you'll have to fab a new skid plate. I haven't made mine yet, but it's going to be a flat piece of steel that is flush mounted with the bottom of the frame on my Scrambler. Should get an extra 3" or so of clearance under there.
3: Currie Twin Sticks
This is how it looks as it came out of the box. It's a pretty simple mechanism that allows the driver to shift the front and rear axles into and out of gear independently. Also included but not pictured is a boot to cover the hole (not sure it will help on my rig) and a nice sticker so you can actually what you're shifting.
Here is the Dana 300 transfer case with the stock linkage partially removed. I would have pictured the whole stock linkage, but my 300 didn't have it with it when I bought it. You need to remove big cross bolt and the plate that allows the single stick to shift both rails.
Actually installing the twin stick shifter is very easy. After the stock stuff is removed, there are two bolts that need to be put through the shift rails and then the main bolt needs to be installed. There are also holes that allow you to adjust the angle of the shifters, either angled forward, backward or straight up. I did a trial fit with them as delivered (middle holes in both top and bottom rails), and didn't need to change it. I did this with the transfer case out of the rig as I was doing other work at the same time, but I'm sure it could be done in the rig too. The image does not show it as I used it, but shows some of the angles at which you can set the shifters.
And here we are all done. Well, almost. The careful observer will notice that I may need to get out the blue flame wrench and heat/bend my shifter for clearance. This is due to the rotation of the transfer case from both the Novak 435-300 adapter and the Go2Guy Twister. But yes, it really is that easy to install. And now I have many more options of how I can run my Dana 300.
If you're looking to run a near bulletproof drivetrain in your rig, I highly recommend all three components used here. Novak's adapter allowed me to mate these two excellent components, while the Go2Guy Twister and the Currie Twin Stick make the setup much more wheeling friendly. Low crawl ratios, increased ground clearance, 2WD-low range - It doesn't get much better than this.