Magnum Box

 The new Offroad Design Magnum Box is our super compact 4 speed transfer case system featuring our "fat shaft" technology that truly equips you to use any of the available ranges without fear of breaking the intermediate shaft.

The Magnum Box is a planetary gear reduction box that bolts to the front of an NP205 transfer case.  This transforms the NP205 from a strong transfer case with poor low range gearing to an extremely strong transfer case with four range options giving you all the low range you could ever want. 

Bolts directly to GM/Dodge fig 8 205, GM round pattern 205 or Ford 205 with no additional adapters.


Ford NP205 version Magnum underdrive kit pictured, also available for GM/Dodge NP205's.

The "Fat Shaft"
  This is the heart of the system and the picture below compares it to the intermediate shaft of all other planetary gearing systems. 
Our "Fat Shaft" is on the the right here, notice that it doesn't ever get smaller than the large planetary output diameter and the shaft is integrated into the input gear.  On the left is a conventional planetary intermediate shaft, notice it necks down to 32 spline.

Until now, all of the planetary underdrive systems use a 32 spline intermediate shaft (or smaller) which is the weak link in the system when using 32 spline outputs.  When that shaft breaks, you're dead in the water until you fix it!

Our giant, US made chromoly intermediate shaft is more than double the strength of a conventional 32 spline connection so it's safe to run in any gear combination.

Available ranges, any of which can be used at any time without fear of breaking the intermediate shaft. 
You get all four choices based on how you shift everything:

Transfer case ratio NP205 range Magnum underdrive range
1:1 Hi Hi
1.96:1 Low Hi
2.72:1 Hi Low
5.33:1 Low Low

Planetary Gear Strength

We know the 205 is strong, so what about the planetary gears?  They're rated for 5500 ft. lbs. of input torque and the six planet gears have huge amounts of gear contact.  They're a proven extremely stout gearset in applications ranging from extreme offroad to today's high power diesel trucks.

Length and Weight

Since the 205 input is integral with the planet assembly, the overall length of the gearbox is a super compact 6.25".  This compact size and high strength aluminum housing construction also make the system amazingly light, adding about 34# to the overall weight of the 205.

While keeping the Magnum underdrive short, we also leave enough room for an adequate oil supply. The Magnum underdrive not only works great for the trail, but is equally happy running many thousands of miles down the road!

So how do you adapt a Magnum Box to your transmission?  The Magnum box either directly bolts to or is easily adaptable to virtually any domestic transmission.  For more info, click here

Tested tough

Matt Thorson beat on our Magnum Box in the 2012 Top Truck Challenge Champions Cup and it didn't flinch!  500+ RWHP LS9, 2.5 ton rockwells with 2" shafts, 54" Baja Claws in the insane Top Truck Challenge, to say it was a trial by fire would be an understatement!

The Magnum Box is the Official Transfer Case System of the 2012 Ultimate Adventure trip and performed flawlessly on the trip in our '99 2500

Check out this article in 4 Wheel and Offroad on the Magnum Box, click here!


Price is $1990

Includes the Magnum housing (fits figure 8 or round pattern NP205), brand new planetary gear set with ring gear and new input gear to match your transmission, input gear/shaft for the NP205, and a shifter mechanism.  These are all the parts to assemble a Magnum system on your big bearing NP205, no adapters needed to bolt to any married NP205. 

Shifters are separate and can be provided by Offroad Design, as can the NP205.

Adapting the Magnum Box to your transmission:

GM TH350 Automatic Transmission:

GM used NP208 transfer cases behind TH350's in the early 80's and the 241 gear reduction box will bolt right in place of the 208.  We also have a short adapter plate that works with TH350's that had NP203's and NP205's behind them.

GM TH700 R4 / 4L60E Automatic Transmission:

Remove the factory NP208 or NP241 transfer case and install the Magnum box with an NP205.  That's it.

GM TH400 Automatic Transmission:

1: Use a TH400 that originally had an NP208 mated to it (this also applies to TH400's that had an NP205 behind them from '85-91). This TH400 uses a 32 spline shaft that sticks out of the case about 2.5" and has an adapter housing that's about 2.5" thick.

2: Use a TH400 that originally had an '84 and older NP205 behind it (this also applies to 2WD TH400's). 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 or a new TH400 to Ford 205 adapter housing that we can supply. 

3: Use a TH400 that originally had an NP203 mated to it.  This TH400 uses a 32 spline output shaft that sticks out about 1-3/8".  We can supply the brand new adapter you'll need to mate the Magnum box to the TH400.

GM 4L80E 4 speed Automatic transmission:

Remove the factory transfer case and bolt the Magnum box with an NP205 in it's place.  That's it.

GM SM465 4 speed Manual Transmission:

1: 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.

2. Use our short SM465 output shaft and adapter (click here).

NV4500 5 speed Manual Transmission:

Remove the factory transfer case and install the Magnum box with an NP205 in it's place.  That's it.

Ford Transmissions (most types):

Remove the factory transfer case and install the Magnum box with an NP205 in it's place.  That's it.

Dodge Transmissions (most types):

Use any Dodge transmission that had a transfer case with a six bolt round pattern on it (NP208, NP241, etc)
.  Any trans that had anything else on it (i.e. NP203, NP205, etc) will likely need an output shaft change and a new adapter system.

Jeep applications:

Use any Jeep transmission that had a transfer case with a six bolt round pattern on it (NP208, NP231, D300 etc).  Remove the factory transfer case and install the Magnum box with an NP205 in it's place.  That's it.

Choose the category you would like more information on.

Doubler™ Dual Transfer Case
Swaybar Correction/Disconnect™ Kit
Shackle Flip™ Kit for ‘67-up GM trucks
Bolt-In Steering Box Brace Kit
1" Body Lift Kit
Competition Style Motor Mounts
Heavy Duty Front Shackles
Chrome Moly Front Axle Shafts
Drivetrain Upgrades
Blazer Soft Tops

Greasable Rear Suspension Bushings
Swaybar Bushing Kits
Body Mounts
Transfer case mounts
Front Upper Shackle Bushing Kit
Spring Bushings
Competition Style Bumpstops
Bushing Assemblies
Tuff Country Suspension
Coming Soon...