NP203/NP205 Doubler Kit
4-to-1 (4:1) transfer case gearing in an NP205/203 package strong enough for big block power and full size trucks.... Or any other really abusive application you can come up with - Chevy, GM, Dodge, Ford or custom!
The Doubler is an all gear, dual transfer case system uniquely suited to full size trucks or other heavy duty, high output/abusive applications because of the durability of its components (all massive helical gears and large input/output shafts). Basically, the Doubler consists of the gearbox section from an NP203 transfer case coupled to a complete 205 transfer case. It's a 3 speed transfer case system, it has options for the 1:1 and 2:1 options that an NP205 would normally have plus a double low range gear of 4:1 with both cases in low range.
3-6 week leadtime
Click on the "product info" tab for ordering details
Adding lower transfer case gearing gives you huge improvements in off road control and torque without affecting your highway gear ratios. Adding the extra gearbox also allows you to run in your normal 2:1 reduction or in super low 4:1 reduction for best performance in any situation. We use a combination of bulletproof and easy to find factory parts with a minimum number of modified components to give you easy bolt together gearing options. Our baseline kit is just the parts to adapt YOUR 203 to YOUR 205, we can also ship complete 203 and 205 units if you like.
The doubler shaft that couples the NP203 to the NP205 is 100% new and US made from 8620 chromoly heat treated steel. The Doubler is only available in 31 or 32 spline which eliminates any weak link in the transfer case system. Very early on we experimented with 10 and 27 spline input gears in the NP205 and they simply didn't hold up. We don't want you to have to buy the kit again when you find the limits of the smaller input gears!
Our doubler adapter is a one piece billet 6061-T6 aluminum adapter housing, we've never had a failure on our doubler adapters. We supply studs for the front face of the NP205 which makes the t-case easier to install and more secure than a bolted connection.
Need a range box for your doubler? We have them HERE
Doubler™ Crossmember Pictures
Here are some pictures of a custom Doubler crossmember built by one of our employees for a GM-GM Doubler with the 2" up rotation. It hangs between 1.5" and 2" below the '83 K5 frame with the 3/16" AR360 skidplate.
This shows the centered mounting on the adapter between the NP203 and TH350. This vehicle uses a TH350 to NP208 adapter with a re-drilled NP203. The single center mount lets the Doubler adapter and the motor mounts control all the torque while the single mount between the 203 and trans helps keep the drivetrain from bouncing and breaking. We HIGHLY recommend a heavy duty poly motor mount set, we keep them in stock!
This is the piece that makes the high clearance setup work. It's shaped just like you see with the entire back plated in to make it stiffer. It uses a urethane mounting puck (available from ORD) on top and bottom of the mounting bracket. The bolts are either tightened into the adapter or running a locknut to allow a preload adjustment on the pucks. This 2 puck arrangement puts a little more "give" in the mounting system and spreads the load over more pucks.
(Click to expand)
Simply choose whether your NP203 range box came from a GM, Dodge or Ford truck.
Dodge NP203's are really the only special case. The GM And Dodge NP203 range boxes are identical, but the GM and Dodge NP203 adapters clock the range box differently. So if you're using a Dodge NP203 with a stock NP203 adapter (i.e. using a 727 or NP435 that already had a 203 on it), choose the Dodge NP203 range box. If you're using a newer transmission that had a transfer case with the six bolt round pattern on it and you're drilling/tapping a new bolt pattern into the 203, choose the GM NP203 range box (even though you're using a Dodge one).
GM NP205's came with either the figure 8 or hourglass pattern (1984 and older) or the six bolt circle pattern (1985-1991). The NP205 needs to be the TH400 version with the short 32 spline input, if it doesn't already have it, we do make an input conversion kit to swap it over. Keep in mind that NP205's with 10 or 27 spline male inputs will need to be disassembled and the housing machined as the larger input gear uses a larger bearing. We offer this service if you do not have a local source to machine your case.
All married Dodge NP205's have the figure 8 or hourglass bolt pattern. It's easy to mistake them as a round pattern case, but if you remove the cast iron adapter on the front of them you'll see they share the same figure 8 pattern as the GM cases (we don't use that cast iron adapter with our doubler kits). All married Dodge NP205's will also have male inputs that need to be converted over to the short 32 spline GM input gear. 23 spline cases will need to be disassembled and machined for the larger 90mm input bearing bore, the GM 32 spline input is a direct swap into 29 spline Dodge NP205's. We carry the 32 spline input converion kits here.
Divorced Dodge NP205's are not adaptable to our doubler kit. Our NP203/NP205 doubler kit marries the front of the 205 to the back of the 203, the divorced Dodge NP205 castings are not setup to marry up to any transfer case.
All married Ford NP205's are ready to accept our doubler kit in factory form, they all have a big female 31 spline input from the factory.
Divorced Ford NP205's can be modified to work, but it's often easier to find the married version. Converting a divorced Ford NP205 to a married one requires the case to be disassembled and bored for the larger 90mm input bearing, the married NP205 bolt pattern drilled/tapped into the face of the case, and sourcing a female 31 or 32 spline NP205 input gear.
Standard rotation is simply the stock rotation. This leaves the NP205 hanging down like it would in a factory application; better for your front driveshaft angle but not as good for belly pan clearance.
The 2" up rotation clocks the NP205 up level with the bottom of the NP203 range box. This buys you 2" more clearance under the belly of the truck but makes the front driveshaft angle steeper. Keep in mind the extra gear box is also adding length so the driveshaft angle often doesn't change much compared to a single transfer case. Rotating the case up can cause floor pan clearance issues in some applications, though in most fullsize trucks that ends up as some clearance work with a hammer at worst.
We also offer rotations for completely flat rotations on a call-in basis. These offer the most clearance possible by rotating the NP203 flat on its side and the outputs of the NP205 level with one another. These require a floor pan to be built around the doubler in just about any application and are usually sold to customers with scratch built buggies.
NP203 ID guide
The New Process 203 was used in GM, Ford, and Dodge through the 70's behind auto and manual transmissions. They were originally a full time 4WD 'case, meaning all 4 tires receive power at all times. This was made possible through use of a differential in the back of the 203 that let the front and rear driveshafts turn at different speeds as just as a diff in an axle lets each axleshaft turn at a different speed.
For off road use, the 203 had a "lock" position in which the differential was locked making the front and rear outputs spin at the same speed. Shift positions are: High, Lo, High Lock, Low Lock and Neutral.
A popular modification to the 203 was to install a "part time" kit to eliminate the differential. In this configuration the 203 operates like more conventional transfer cases in that it's either in 2WD or 4WD and when in 4WD the power is evenly split from front to rear.
The NP203 is identified by several features:
1. The transfer case is made up of 4 sections bolted together, a range box (the gear reduction we use for the Doubler kit), the chain case which houses the chain drive to the front driveshaft output, the differential housing, and the output housing. The front 2 sections are cast iron, the back 2 sections are typically aluminum.
2. The overall length is about 22-23" from the face of the case to the rear output yoke centerline.
3. The shifter is a somewhat complicated box that actuates the 2 levers on a single shaft on the side of the range box section of the 203.
4. The model tag (if it still exists) will be found on the front of the chain case above the front output shaft. It will list the model number, the manufacture date and the gear ratio.
NP205 ID guide
The New Process 205 was also used extensively in GM, Ford, and Dodge. GM and Dodge used the 205 in some trucks into the early 90's, Ford stopped using the 205 in 1979. The 205 is a part time 4WD 'case, meaning when it's in 2WD the front driveshaft will not receive power. It has 4 stock shift positions, 2wd Hi, 4WD Hi, Neutral, and 4WD Lo.
NP205 cases had several different configurations with Ford and Dodge using both married and divorced models and GM using many different input spline types and 2 different bolt patterns.
The NP205 is identified by several features:
1. The transfer case is one piece of cast iron. There is a short bearing retainer/output housing at the tail of the case, and aluminum bearing retainers/seal retainers at the front and rear outputs but the working parts are all in a single iron housing.
2. There is a small idler shaft cover on the back of the 205 with 3 small bolts holding it on. This is somewhat unique among transfer cases.
3. The overall length of the NP205 (in fixed output yoke versions) is about 12-13" from the front of the case to the center of the output yoke.
4. The shifter is a very simple lever operating a crossbar between the two shift rails that plunge in and out of the front of the case.
The ID tag is found above the front driveshaft output, and will list model, manufacture date and gear ratio.
Adapting a TH350 to the NP203 range box
1. Many NP203's came already bolted to TH350's, if that's what you have, this part is done.
2. TH350's that were attached to an NP205 have the same output shaft as the NP203 application. All you need is a TH350/NP203 adapter plate and a TH350 version NP203 and it all bolts up.
3. You can use a TH350 that was attached to an NP208. You'll need an NP203 with a 27 spline input (TH350 version) and the face of the NP203 range box needs to be drilled/tapped with the NP208 bolt pattern (you can use the adapter as a template). The machine work on the adapter and the NP203 bearing retainer will line everything up, so the bolt pattern doesn't need to be machine-shop perfect. The idler shaft needs to be retained as well (simple tab to keep it from falling out).
2WD TH350's don't work and will need to be torn down and a 4WD output shaft installed.
Adapting a 700R4 or 4L60E to the NP203 range box
1. With a 4WD 700R4/4L60E you'll need an NP203 with a 27 spline input (TH350 version) and the face of the NP203 range box needs to be drilled/tapped with the stock t-case bolt pattern (you can use the adapter as a template). The machine work on the adapter and the NP203 bearing retainer will line everything up, so the bolt pattern doesn't need to be machine-shop perfect. The idler shaft needs to be retained as well (simple tab to keep it from falling out).
2WD 700R4/4L60E's need to be torn down and a 4WD shaft installed
Adapting a TH400 to the NP203 range box
1. Some TH400's came with NP203's attached to them, if that's what you have, this part is done. These mostly came in '77-79 GM K20 and K30 trucks.
2. Use a TH400 that was attached to an NP208. You'll need an NP203 with a 32 spline input (TH400 version) and the face of the NP203 range box needs to be drilled/tapped with the NP208 bolt pattern (you can use the adapter as a template). The machine work on the adapter and the NP203 bearing retainer will line everything up, so the bolt pattern doesn't need to be machine-shop perfect. The idler shaft needs to be retained as well (simple tab to keep it from falling out).
3: Use a TH400 that originally had a NP205 behind it. This TH400 uses a 32 spline shaft that sticks out about 4.5". You'll need to use a factory TH400 to round pattern NP205 adapter housing that is 4" thick and once again, re-drill the front face of the NP203 to match the round pattern. The input gear will be the TH400 version NP203 32 spline input. Drawbacks to this system are the overall length with the 4" housing between the two and the expense of buying the factory housing. They're not common as used parts and typically must be purchased new. ORD can supply this adapter.
Adapting a 4L80E to the NP203 range box
With a 4WD 4L80E you'll need an NP203 with a 32 spline input (TH400 version) and the face of the NP203 range box needs to be drilled/tapped with the stock t-case bolt pattern (you can use the adapter as a template). The machine work on the adapter and the NP203 bearing retainer will line everything up, so the bolt pattern doesn't need to be machine-shop perfect. The idler shaft needs to be retained as well (simple tab to keep it from falling out).
The slip yoke style 2WD 4L80E output shaft can be cut down to mimic a 4WD shaft, the fixed yoke style 2WD 4L80E output shaft needs to be changed out for a 4WD one.
Adapting the GM SM465 to the NP203 range box
1: Use a factory configuration. GM mated the NP203 to the SM465 in 1973-1975 using the 10 spline output in the 465, a 10 spline female input in the NP203 and a 4.25" adapter housing between the two. This configuration was used in a wide range of GM trucks but is somewhat rare. Problems are the 10 spline connection tends to wear in the long term and it's difficult to find. Positives would be the short length and the ability to use the common 10 spline output in the transmission.
2: Use a SM465 that was originally mated to an NP208 transfer case. This 465 will have a 32 spline output shaft with a 8 3/8" adapter housing. You'll use a NP203 gearbox with a 32 spline input gear and the face of the 203 drilled and tapped with the GM round bolt pattern to match up to the factory 208 adapter housing. This works very well if you have the available length in the vehicle since the parts are commonly available and the 32 spline connection is very strong and durable, we have brand new adapter housings.
3. Use the factory SM465 to NP203 adapter housing or a brand new adapter housing that we can provide (click here)with ORD's new 32 spline SM465 output shaft and a 32 spline input gear in the NP203 (click here). This allows the shortest overall length with the highest strength, most durable spline connection.
Adapting the GM NV4500 to the NP203 range box
With a 4WD GM NV4500 you'll need an NP203 with a 32 spline input (TH400 version) and the face of the NP203 range box needs to be drilled/tapped with the stock t-case bolt pattern (you can use the tailhousing as a template). The machine work on the adapter and the NP203 bearing retainer will line everything up, so the bolt pattern doesn't need to be machine-shop perfect. The idler shaft needs to be retained as well (simple tab to keep it from falling out).
Adapting most Ford transmissions to the NP203 range box
Conveniently for us, Ford used an identical round bolt pattern and 31 spline output shaft for all of the truck type transmission and transfer case combos. This means you can take your Ford NP203 and bolt it directly in place of most Ford transfer case without adapter and shaft changes. This also seems to carry into late model trannies also. If only GM used this system!
There are a couple of different output housings available for the back of the C6 that you should be aware of, info is a little sketchy but we know of at least 2 lengths, one is about 7" long and the other is about 5" long. The output shaft length must match the output housing length. Otherwise you can bolt a Ford NP203 gearbox directly in place of the Ford NP205, NP208, or even the newer aluminum cases.
Adapting most Dodge transmissions to the NP203 range box
Dodge used the NP203 with the NP435 and the 727 auto tranny through the '70's. These combinations are still relatively easy to come by as used parts. All Dodge 203s use a 23 spline input gear. Later model Dodge transfer cases use a round bolt pattern similar to the GM round pattern. This pattern is adaptable to the front of the Dodge NP203 with re-drill work similar to the work on the GM 203 bolting to a GM round pattern.
|NP203 NP205 Doubler Instructions||1.1 MB||Download|