Dual Transfer Case Systems
"Doubler" NP203 Reduction based systems
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Example of a "Doubler" system: NP203 reduction unit mated to an NP205
These systems are quite cost effective when you already have some of the major ingredients of the system.
This system adds in an additional gearbox between the transmission and transfer case. A common transfer case from the 70s, used by Dodge, GM and Ford, the NP203 is a two-section unit. The front section houses the reduction gears and the rear section houses the chain and parts to control power flow to the front vs. rear axle. This front section can be split off, and with an adapter housing and a special shaft it can be bolted in front of several different transfer cases. Since the NP203 has a reduction ratio of 1.96 to one (approximately 2 to one), when shifted in it will roughly DOUBLE the reduction of your transfer case. Thus it is called a "Doubler". It can also be used with the transfer case in high range allowing a 1.96 to one low range in 2WD or 4WD.
FAQ: What Parts will I need?
You will need a transmission with the correct adapter to mate up to an NP203, or you will need to purchase an adapter. There are few aftermarket adapters for applications such as NV4500, and there are Ford, Dodge and GM Factory transmission adapters. Some of these adapters are getting scarce, depends on the trans you want to mate up.
You will need and NP203 "donor" case. From this, the front reduction housing and the gears in it are used. The 203 used should match up to the adapter you are using. There are a number of different factory 203 adapter combos.
You will need a Tcase to mate the 203 "Doubler" to. Most common are NP205s, although it is also possible to mate up to T-cases such as the Dana 300 or Atlas. Your rear case will need to have a 31 or 32 spline input. This is the standard size on the Ford 205, it is one of the available OEM options for the GM 205, and the Atlas Tcase. A Dodge 205 will require modifications and is thus not optimum. 32 spl input is available from us to fit the Dana 300.
Next, The "Doubler" adapter kit. This is the parts kit that mates up the "doubler" unit (front reduction box from the 203) to the transfer case. Depending on which NP203 you have and which Tcase you want to use, shaft and adapter configurations vary, with most costing $750 for the kit.
A Shifter for the doubler will be needed. You can fabricate something to shift the doubler, or a shifter is available, typically $175 depending on the exact application.
If you have most of or all of the first three parts, it
is generally excellent bang for your buck to choose a doubler system. If
you need to buy these components, the cost can start stacking up the where
a more no compromise, all new system such as the Klune-V Extreme
underdrive should be considered.