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​   Other models of the NP205 had a "Figure 8" 8 bolt pattern, instead of the round 6 bolt pattern, and could have had a male input shaft. To use these NP205 versions with the Strong Box, you would need to swap in a female input shaft, and specify when you order that you need a Strong Box for a Figure 8 NP205. 

   The picture at left shows our Figure 8 version. There are 5 of the 8 bolts used in the Strong Box. There is no extra charge when you order this Figure 8 version. We recommend adding a mount to support the added weight, no matter which version you order. 

   We also offer Figure 8 to Round 6 bolt adapter plates that would allow you to utilize all 8 bolts, if you feel its necessary. Figure 8 to Round 6 Bolt Adapter Plate costs $175.00, and adds 3/8" length to the overall assembly. 

   Our standard length Strong Box Underdrive can mount to nearly any domestic transmission and transfer case. Ford, GM, Dodge, and Jeep transmissions and transfer cases with the round 6 bolt pattern, and a female input shaft, can bolt to the Strong Box.

    There are 3 sections to the standard Strong Box housing. First, the gear housing. Next, the shifter housing. Finally, the clocking adapter. Each section has multiple universal bolt patterns which allow nearly infinite clocking positions for your Strong Box shifter mechanism, and for your transfer case. 

   Some models of the NP205 transfer case came with a long (about 4" of stick out) female 32 spline input shaft. This is one exception. To use this NP205 with the Strong Box, you would need an additional 2.0" long spacer, or swap in an NP205 short female input shaft. 

​​​  4340 alloy steel is mainly used for manufacturing landing gear for heavy aircraft. Our 4340 thru hardened shafts come with a Limited Lifetime Warranty* against breakage. 

   We use a rear bearing to support the output shaft, and keep all components concentric.

​    Our line of 2.72 Strong Boxes are designed to use gears from the following transfer cases:

NP241, NP243, NP246, NP231, NP233, NP236, and a few others that are very similar.  

​   To use NV271 or NV273 gears in the 2.72:1 Strong Box Underdrive, you simply need to order your Strong Box specifically for NV271 or NV273 gears. We will make sure your Strong Box gear housing has the proper dimensions for NV271 / NV273. If you have already received a housing machined for NP241 or similar gears, we can modify it to accept NV271 / NV273 gears easily, and at no additional charge. You only pay shipping cost. NOTE: A NV271 / NV273 housing cannot be modified for NP241 or similar gears. 

Other cases that can be used, but may require slight modifications include:

NP261, NP263, NP241 DLD, and a few others that are very similar.  Click Here to learn more about some of the required modifications to use these gear sets. 

    This allows the 2.72:1 Strong Box to be ordered with any of the following input shaft spline counts, making it compatible with many domestic transmissions:

  • 21 spline Jeep
  • 23 spline Jeep / Dodge
  • 24 spline Ford
  • 27 spline Chevy
  • 29 spline Dodge
  • 31 spline Ford
  • 32 spline Chevy
  • 34 spline Ford

Don't see the spline count that your transmission output requires?...

Keep looking on our site, we have other options available, and more to come. Feel free to Contact Us with your custom need. 

Strong Box DIY kit $699.00
​Pre-Assembly / Good, Used Gears $300.00

Some transfer cases may require trimming of the input shaft length, or transmission output shaft in order to get proper fitment.

Universal Strong Box Underdrive Standard Length

   Our 2.72:1 standard length Strong Box Underdrive is the most versatile​ and universal of all of our torque multiplying gear boxes. 

   Measuring only 7.9" long X 7.9" diameter, and weighing 36-39 pounds, it's hard to belive that it is capable of handling up to 7,890 ft. lbs. of torque...   BUT BELIEVE IT!