Transfer Case Doubler Kit - Double Down

Here you can see our completed 203/205 doubler setup. Though not quite as compact as some other low-gear transfer-case arrangements, this unit with its massive helical gears and large input/output shafts can survive under serious abuse and high horsepower.

Designed for fullsize trucks or other heavy-duty/high-output applications, the ORD doubler transfer-case system consists of three stout parts: the gearbox section from an NP203, the ORD adapter plate, and an NP205 transfer case. This system provides an additional low-range ratio of 2:1, which, when added to the existing NP205 low-range ratio of 2:1, equates to a final crawl ratio of 4:1. This combination of gearing gives any applicable vehicle improved crawl control and torque multiplication without affecting your high-range cruising speed and rpm. Thanks to the popular use of the NP205 transfer case in Chevy, Ford, and Dodge pickups, this setup can work in a bunch of different applications. The system uses a combination of trail-proven, readily available factory parts, along with a few custom components built by ORD. We like the fact that the system was designed to handle big-block power without grenading. But most of all, we like the fact that this complete 4:1 system costs significantly less than other low-gearing transfer-case options available today. Altogether, this project would have cost us $1,629 to complete (not including labor).

1. The best NP205 transfer case to use for this project is the one found behind the Turbo 400 and SM465 transmissions from '86-and-newer 1-ton GM pickups. If you don't have or can't find a TH400-version 205, Off Road Design has the parts you will need to convert your TH350-version 205 to a TH400 type.

2. This is the complete doubler kit as it was shipped to us by ORD. Our initial inspection of the instruction booklet left us wondering if we should have asked an experienced shop to help out with the installation. However, after familiarizing ourselves with each individual component of the kit, our confidence level increased and we were ready to tackle the project in our home garage.

3. The kit requires the gearbox portion (first 6 inches of the case) of a NP203 transfer case. Luckily, these cases are readily available at just about any domestic wrecking yard in the country. We paid $300 for this used one out of a '70s-era Chevy 3/4-ton pickup. ORD recommends getting a 203 from a '73-'77 pickup equipped with the Turbo 400 automatic transmission. This is preferred because it has the strongest input shaft available (32-spline) on NP203s. For additional transmission/transfer-case configurations, visit ORD's technical Web site.

4. With the NP205 we had it was necessary to do some minor machine work on the input-bearing retainer (case). This was due to the fact that our 205 originally came behind an SM465 transmission. ORD supplied us with the necessary parts to convert our 205 to the beefier Turbo 400 version. The machine work ensured fitment of the new larger Turbo 400-style input bearing and shaft. To do this, we had to completely disassemble the transfer case. Once apart, we had the empty case magnafluxed in preparation for machining. Here, you can see the material being taken off by an end mill.

5. This is how the new input bearing looked once installed after the machine work was completed. We went ahead and rebuilt our NP205 while we had everything apart. You can purchase a similar rebuild kit for around $170.	6. With each component ready to go, we started by installing the aluminum adapter bearing. This required us to heat up the aluminum adapter with a torch prior to tapping in the new bearing shown here. The fit was very tight.	7. Next, we installed the intermediate gear cluster back inside the 205's case. This was followed by both the input and output gear clusters.
8. Then we installed the doubler's low-range gear and output shaft into the input hole of the 203 range box. Once installed, it was time to mate the 203 range box to the doubler adapter. The first step was to apply a good bead of RTV sealant to each side of the adapter gasket. Hint: do one side at a time.	9. This was the hardest part of the installation. The 203 range box gear/shaft assembly requires that several small needle bearings be installed on the interior of the shaft. To do this, we used a healthy portion of thick red bearing grease to help hold each bearing in place. Once all the bearings were installed, the doubler adapter and the 203 range box were mated carefully together.	10. We also installed a thick bead of blue RTV silicone to seal off the PTO access plate on the 203 range box. You will notice there's a port incorporated into this PTO block-off plate-this provision allows you to fill the range box with gear lube.
11. Here, you can see the new adapter plate bolted to the 203 range box. The next step is to mate the 205 to these two. Once connected, we had to use caution while moving this mammoth around because the additional components added a significant amount of weight to the already heavy NP205 transfer case.

Other Necessary Modifications

The doubler transfer case is not an afternoon bolt-in because of all the little details involved. Some things that should be addressed are:

Floorboard clearance
You may need to modify your floorpan, install a short body lift, or lower the transfer case to get the proper floorboard clearance with this kit in some vehicles. A combination of the above may work also. Floorboard clearance is rarely a major problem, but you should be aware of the possibility. We found the ORD Triple Stick shifter worked out nicely between the two front seats of our buggy donor vehicle. However, this may add a significant amount of time to the installation process in other vehicles.

Crossmembers
Crossmember modification will likely be required due to various frame changes when the crossmember is moved. Also, while a single crossmember under the 205 is adequate, dual additional crossmembers are strongly recommended. The front crossmember will likely require a loop or tunnel for front driveshaft clearance. Custom fabrication is required to completely skidplate the transfer-case setup. Ideas on high-clearance crossmember mounting can be found on ORD's Web site.

Speedometer Cable
You may need a new speedometer cable to reach the transfer case in the new position. They are available from the dealership or a parts store.

Exhaust
Some exhaust systems run near the transfer case or driveshafts and will need to be modified for clearance.

Driveshafts
You will probably need a longer front and shorter rear driveshaft with the doubler setup. If your shafts are in good condition, you can probably just have them rebuilt to minimize extra cost. This is a good time to look at U-joint and yoke upgrades also.

Breakdown of costs: