Old is Gold: Why Rufus has a 52 year old Transfer case
Features & considerations for our 1973 NP205 transfer case
As an integral part of a 4wd system, it may seem odd to rely on a piece of machinery from 1973 as a base of our 4x4 swap…in a brand new truck! In this post we consider different transfer case options and explain why in this case, old is gold.
Why does Rufus need a transfer case, anyway?
Rufus was bought stock as a two-wheel drive (2wd) truck. Four-wheel drive (4wd) wasn’t something we were willing to compromise on with this build, and without a good option to buy a new cab over truck in 4wd, we decided to build our own. Comparing simplified 2wd and 4wd vehicles there are 2 major differences: (1) front axle; (2) and transfer case.
A transfer case is an additional gear box that “transfers” power to the front and rear axles. It is generally aft of, and most often attached to, the transmission. In most 4wd setups the transfer case allows you to select between 3 different modes of operation 2wd, 4wd high range, and 4wd low range. It divides the power forward or aft and when in low range uses a gear reduction to transfer more torque to the axles. Deciding what transfer case to use and how to modify the truck to accept it was a large undertaking, with lots of things to consider.
What features we wanted
With the thought of global or long-term travel, we want Rufus to have a robust off-the-shelf available 4wd system, that includes the transfer case. We were looking for high and low range, the ability to run front or rear wheel drive, ease of maintenance, and simplicity. If needed, we wanted parts to be easily available, to allow for repair on the road. While transfer case drop (side of the transfer case where power goes forward) is also a major consideration in transfer case selection, we were also installing a new front axle, meaning we could choose which side the differential is on, making this less important in our situation.
Rufus is equipped with a GM 6l90 transmission, this 6 speed automatic has been used in cars and trucks since 2007, some of these trucks are even 4wd. Great! We can source and install a factory transfer case…..Not so fast! To attach a factory transfer case to the back of our transmission we would have to modify or replace the output shaft and tail housing. Although we are ripping apart a brand new truck, we do draw a line at transmission disassembly, we would like to leave our brand new transmission alone, thanks. This means a married transfer case was not an option, and Rufus was going to need a divorced transfer case.
Transfer cases we considered
Even though we decided not to attach a transfer case we looked into what could be fitted. A good modern option is the mp1226, a married, chain drive, with a 2.72:1 low range, and electric or manual shift that came in gas and diesel GM trucks. But we wanted a gear driven transfer case, when compared to a rubber band (chain drive) it is far more robust, so this option was out. We considered using an aftermarket adapter to marry a gear driven transfer case, but again, decided to avoid transmission disassembly.
In the divorced realm of transfer cases, the dana 200 or New Process 203 (NP203) would make good options. Both gear driven, and both available as a divorced case. The dana 200 is built with straight cut gears making it extremely strong but equally as loud, and the NP203 is hard to find as a divorced unit.
An Atlas or Hero aftermarket transfer case would make a very good option, they are built to take a beating, can be ordered with a plethora of low range gear options, and are available married or divorce. But these cases are custom built with proprietary parts and super expensive.
Our choice: 1973 NP205
We went with a NP205, well known as the rock crusher of transfer cases. Our specific case came out of an early 70’s Dodge 300. It is super simple, gear driven, and known to be one of the most robust production transfer cases around. It was sold in millions of trucks from the 60’s through the 90’s and in its stock form checked every box except the not-so-low, low range gear of 1.96:1. I found someone on marketplace selling 2 cases needing to be rebuilt for $150. I picked the better case, rebuilt it, and so far so good! Check back for a more in-depth post on what we did for the rebuild, how we modified the truck to accept the transfer case, and what we have planned next!
