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Factory Replacement Transfer Cases
Atlas Transfer Case (2spd and 4Spd)
Stak "Monster Box" T-cases (2 & 3 spd)
Left Drop Dana 20 - NP231 replacement
NP241OR - "Rubicon" Tcase
Low Geared Transfer Cases
(Low gear sets available for NP231, Dana 18, Dana 20, Dana 300, others)
Jeep NP231 "Enhanced" Tcases
(Lower gears, Slip yoke eliminators, HD chain kits)
Dana 300 Transfer Case Conversions
Factory Replacement T-Cases
Complete re-manufactured transfer cases are available in most makes and models, domestic or foreign.Atlas Transfer Case
Manufactured by Advance Adapters, these units are manufactured in 2 and 4 speed models with various gearing options available. 2 spd unit available for many popular applications in 2.0, 3.0, 3.8, 4.3, 5.0 and 6.0 to one ratios. 4 speed unit available in wide 5.4 ratio or close ratio up to 10.34 ratio. Custom adapted applications are in many cases possible where the standard stock item will not fit. We know all sorts of unusual applications for these excellent cases.Stak Transfer Cases
The Stack "Monster Box" is a Large, very stout T-case, in 2 and 3 speed models, with various gearing available. These are Large and Stout. Full Size Truck, High Horsepower, big tires. I call this the "MaxiMonster"
StaK also Manufactures "MiniMonster" T-cases, both in 2 speed and 3 speed versions, somewhat smaller than the original Monster (MaxiMonster), built of a size so you can fit it into Jeeps and such
Left Drop Dana 20
We offer a version of the Dana 20 all gear drive transfer case configured for use in a Wrangler, replacing the chain drive NP231 case. This case is only 11.5" long, compared to 21" for a stock NP231, making possible combinations of transmissions, underdrives and lots of lift, while retaining good driveshaft length. Available in 2.34:1, 2.46:1, 3.15 to one versions. It comes equipped out of the box with fixed CV type yoke front and rear. Versions available for either twin-stick operation or operation form factory Wrangler type shift lever.
Wrangler/Cherokee applications: With the adapter it bolts right up where an NP231 came off. We can supply a unit that will work with a stock wrangler Tcase shifter, you will need to extend your link rod, or use a piece of all thread with some heim joints. (Twin stick also doable, see the Bronco Dana 20 Data Sheet) Your vehicle speed sensor can be modified and hooked up with a short adapter cable, so your speedo and computer will work properly. You will need a CV rear driveshaft, with a slip in the driveshaft, as the D20 is fixed yoke out. We can supply a kit with all the needed parts. Your front driveshaft will need to be shortened. The Tcase is quite a bit smaller than the 231, so There are no clearance issues.
NP241OR - "Rubicon" T-case
The same Tcase, brand new, as used in the new Jeep Wrangler "Rubicon" 4:1 ratio, factory HD components. Unless you can get a good price on one, or need a replacement unit for your Rubicon, the Atlas is a better Tcase at a similar price.
Jeep NP231 "Enhanced"
The NP231 is the transfer case supplied from the factory in all Jeep Wranglers (Except the "Rubicon" edition. While these transfer cases are extremely reliable in an unmodified or near stock Jeep, as the vehicle becomes more radical, short comings begin to develop. There are three primary areas that are addresses. Gear ratio, output shaft problems and chain durability. The advantage of upgrading an NP231 or purchasing an upgraded NP231 for your Jeep is that it is a direct bolt in.
Note: When extensive upgrades are considered the costs begin to stack up. It is frequently more "bang for the buck" to upgrade to an Atlas Tcase or Install a Klune-V Extreme Underdrive
Slip yoke eliminator
These cases almost always come from the factory with a slip-yoke output. As the suspension in the jeep moves up and down, the driveline needs to become shorter and longer to accomodate this. The low cost way to do this is to use a "slip yoke" on the rear of the transfer case. This slip yoke works fine when driveline angles are minimal: The pressure on the slip yoke is more or less straight in and out. However, when driveline angles exceed stock, the slip yoke tries to operate at an angle: When the rear axle bumps up going over a bump, the force pushing on the slip yoke is at an angle, and tends to bind. This frequently causes the transfer case housing to crack. Any time a driveline gets much of any angle on it, you want to get rid of that slip yoke. It saved the factory a few bucks, but is no good for us. (you will also need to modify or change the driveshaft to a unit that has a slip joint in it: That length change when the axle goes up and down has gotta go somewhere!)
Note: It is also better to upgrade to a 32 spline output shaft when doing slip yoke conversion. The factory 27 spline shaft will work, but is marginal in strength. High Impact always uses 32 spline mainshaft when doing this conversion.
4:1 Ratio Gearset
This is a relatively low cost way to improve rock crawling gearing performance. Pros and cons of conversion to a 4:1 gearset in an NP231 are covered in the article "A systems approach to 4WD gearing"
Upgrade to HD Chain
Power to the front axle is transmitted to the front driveshaft via a chain inside the transfer case. This chain is adequate and reliable in stock or near stock applications. When we increase tire, engine power or gearing, we begin to stress this stock chain beyond reliable parameters. It is possible to replace the chain and its sprockets with larger components. High Impact offers this upgrade both as a kit and included in complete custom NP231 transfer cases
Dana 300 T-Case Conversions
Left Drop Dana 300
Gear drive, short replacement for NP231 in later model Jeeps. Also can be built with 4:1 gears. This definitely an option to consider if you already have a good Dana 300. Coupled with the cost of a fresh 300, the cost of a flip kit and the cost of the low gears, it starts to make more sense to buy the Left Drop Dana 20, an Atlas or a Klune-V Underdrive system.32 spline input Dana 300
Beefed up input fits HD Chevy tranny spline.HD output shaft
The Dana 300 is really quite a strong case. Its Achilles heel is the 27 spline output shaft, which has been known to break off in extreme applications. We can build a 300 with a 32 spline output shaft. The parts and kit are also available separately.4:1 Gearset
The 2.6 ratio gears can be replaced with 4:1 ratio gears. Discussion of the uses of this conversion, as well as pros and cons are treated in the article "A systems approach to 4WD gearing"
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Left-Drop Dana 20 Gear Drive Tcase adapted for Wrangler 231 Replacement
Atlas 2 & 4 spd Transfer Cases
StaK "Monster Box" 2 & 3 spd Transfer Cases
NP205 Ford Pictured. Chevy variations also available
NP241OR "Rubicon" 4:1 Transfer case
