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T-Case Upgrades: Common Problems and Cures for Popular 4x4 Transfer Cases

Posted in How To: Transmission Drivetrain on August 21, 2017
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Photographers: Courtesy of Manufacturers

At the heart of every true 4x4 is a transfer case. The transfer case receives power from the engine via the transmission and then splits it to the front and rear axles, but not all transfer cases are created equal. There are many different designs that have been utilized over the years to send power to the front and rear of our 4x4s. Some transfer cases, such as the venerable NP205, have become champions of the heavily modified off-road kingdom, while others are problematic even in stock applications. Each transfer case has pros and cons, but fortunately the aftermarket has embraced the most prevalent transfer cases and granted them an abundance of aftermarket add-ons to improve performance and reliability. We’ve compiled some of the more popular and noteworthy transfer cases here along with the modifications you might need to consider making to the splitter in your 4x4.

BorgWarner 1356
The BorgWarner 1356 transfer case can be found in many different Ford 4x4s offered from 1980 through 1996. There is a manual-shift version and an electric-shift version. The shifting mechanism on the electric version can be problematic, however the replacement shift motors and other components are still readily available from companies like Bronco Graveyard (broncograveyard.com). If you have become tired of replacing the expensive push-button electric-shift motors, your 4x4 can be converted to a manual-shift transfer case by either swapping in a manual version of the 1356 or by using the twin-stick conversion kit from Behemoth Drivetrain (behemothdrivetrain.com). This kit is also designed to work on the BorgWarner 1354.

Dana 300
The last Dana 300 rolled off the assembly line more than 30 years ago, but it’s still a very strong and popular transfer case to swap into lightweight 4x4s. It can be found in ’80-’86 Jeep CJ models and ’80 International Scouts. The most common failure point on the Dana 300 is the 1 1/8-inch-diameter 26-spline rear output. It’s not that the output is particularly weak, it’s just that it is susceptible to breaking if it’s overpowered or there is driveshaft U-joint binding caused by axlewrap or unrestrained suspension movement. Companies such as Advance Adapters (advanceadapters.com), Novak Conversions (novak-adapt.com), JB Conversions (jbconversions.com), and TeraFlex (teraflex.com) offer 1 3/8-inch-diameter 32-spline heavy-duty rear output shaft upgrade kits. JB Conversions also offers a heavy-duty 32-spline front output shaft kit for the Dana 300.

If the respectable 2.62:1 factory low range of the Dana 300 is not enough for your application, JB Conversions and TeraFlex both offer 4:1 low range gearsets to help multiply your gearing and increase your 4x4’s overall crawl ratio.

The stamped-steel factory Dana 300 oil pan is prone to warping and leaking. You can curb oil seep, increase fluid capacity, and promote better heat dissipation with a billet aluminum oil pan from Novak Conversions.

The Dana 300 is strong, but it has its limits. Heavy 4x4s with low gears, big tires, and high horsepower output may cause the factory cast-iron Dana 300 case to split in half. If this is a concern or problem, you can upgrade to a Behemoth Drivetrain billet 6061 aluminum Dana 300 Colossus Case. It should be available by the time you read this.

Dana 20
The Dana 20 is an often overlooked, yet admirable transfer case given its compact size. The simple design makes it a great candidate for an at-home rebuild. Versions of the Dana 20 were offered in Chevy, Ford, and International Harvester vehicles, although the Jeep version is by far the most common. Subsequently, the Jeep Dana 20 enjoys the most aftermarket support.

The Jeep Dana 20 has several weaknesses. The one most often noted is the somewhat pathetic 2.03:1 low range ratio. TeraFlex offers a 3.15:1 ratio low range gearset for the Dana 20. The 1 1/8-inch-diameter coarse 10-spline front and rear outputs are another potential weak spot. Advance Adapters offers a 1 3/8-inch-diameter 32-spline rear output shaft kit that fits the Jeep and Scout Dana 20. Novak Conversions has an increased capacity billet aluminum oil pan that fits the Jeep, International Harvester, and Chevy Dana 20 transfer cases.

NP205
The NP205 has long been considered the ultimate transfer case, but there is still room for improvement, especially in really extreme heavy-duty, high-horsepower, and big-tire applications. The NP205 was used from the ’60s through the ’90s in Dodge, Ford, and GM fullsize trucks. Various bolt patterns, input shaft diameters/spline counts, as well as output shaft diameters/spline counts were used over the years depending on vehicle make and application. Offroad Design (offroaddesign.com) has many parts available to adapt and upgrade the NP205. The weaker 10-spline and 30-spline factory front outputs found in some NP205 transfer cases can be upgraded to a factory heavy-duty 32-spline front output. An aftermarket 32-spline fixed-yoke rear output is available for the later versions of the NP205 that came from the factory with the less-desirable slip-yoke. Other Offroad Design products for the NP205 include a billet rear output bearing retainer and a heavy-duty rear output shaft. NorthWest Fabworks (northwestfab.com) offers monster 1 3/4-inch-diameter 34-spline Titan Series front and rear output shafts with billet bearing retainers for the NP205. NorthWest Fabworks also offers a 34-spline input for the divorced NP205 and full-billet bearing retainer and rear cover kits to replace the crack-prone cast parts. Behemoth Drivetrain offers the 1 1/2-inch-diameter 35-spline Juggernaut Series front and rear outputs, Big Stubby 35-spline outputs, as well as the billet 6061 aluminum Colossus Case to replace the stock NP205 cast-iron case.

If the factory 1.96:1 low range ratio of the NP205 is inadequate, JB Conversions offers the LoMax 205 replacement gearset and heavy-duty ductile iron case to bring it down to a respectable 3:1 ratio.

NV231
The NV231 has probably been used in more Jeep vehicle applications than any other transfer case ever offered. As such, there is a complete smorgasbord of aftermarket upgrades available. Both GM and Dodge also used the NV231 in several different midsize and fullsize 4x4s over the years. Many of the NV231 upgrades are interchangeable between the Jeep, GM, and Dodge transfer cases.

The body-mounted shift linkage on some NV231 applications can become problematic and not function properly, especially when worn or when combined with body lifts or aftermarket replacement skidplates. Advance Adapters, TeraFlex, and Novak Conversions all offer shifter brackets or linkage that cures this shifting problem.

Lifted short-wheelbase Jeeps with the NV231 like the Wrangler don’t do well with the factory slip-yoke and driveshaft. A slip-yoke eliminator kit and CV-style driveshaft will provide a much more comfortable and reliable vibration-free ride. Slip-yoke eliminator kits are available from companies such as Advance Adapters, Rough Country Suspension (roughcountry.com), Rubicon Express (rubiconexpress.com), Rugged Ridge (ruggedridge.com), and Tom Wood’s Custom Drive Shafts (4xshaft.com). For heavy-duty applications, look for a 32-spline slip-yoke eliminator kit.

The internals of the NV231 can also be beefed up for more torque, weight, and horsepower. JB Conversions offers a six-pinion planetary and a wide-chain kit for the NV231.

Vehicles that frequent really tight and technical trails with lots of sharp turns can benefit from a two-wheel-drive low range transfer case setting. It gives the 4x4 the ability to turn sharper without the drivetrain bind associated with four-wheel-drive low range, especially on hard surfaces. TeraFlex offers two-wheel-drive low conversions that fit several models of the NV231.

NV241
The NV241 is probably one of the most underrated late-model transfer cases available. It’s incredibly durable, features a torque capacity of more than 5,500 lb-ft, and was available in many different model fullsize trucks and SUVs. Some Dodge versions of the NV241 come from the factory with a fixed rear yoke, but most have the less desirable slip-yoke. Slip-yoke-style NV241 transfer cases can be easily upgraded to a fixed yoke with kits from companies like JB Conversions, Offroad Design, and Tom Wood’s Custom Drive Shafts.

NV241OR
The NV241OR is the factory transfer case that only comes in the Wrangler Rubicon. It features a formidable 4:1 low range gear which makes it great for slow-speed technical crawling. All NV241OR transfer cases feature heavy-duty fixed yokes front and rear, but the aluminum housing has been known to be susceptible to cracking when running bent, unbalanced, incorrectly angled, or worn-out driveshafts. The real cure to this problem is to keep an eye on the driveshafts, but Rock-Slide Engineering (rockslideengineering.com) has developed a girdle to help stiffen the NV241OR and even help protect it from complete flinging driveshaft failure.

NV242
The full-time, part-time, and low range 4x4 capability make the NV242 an extremely versatile transfer case. Versions of the NV242 can be found in GM and many Jeep 4x4s as well as in the Hummer H1 and H2. The torque-biasing full-time 4x4 feature is a huge asset in areas that see a lot of patchy snow- and ice-covered roads, while the part-time shifter position provides true 4x4 off-road performance. Unfortunately, the full-time feature that makes the NV242 desirable also makes it weaker and undesirable for a heavily modified 4x4 with big tires. There are no upgrades to increase the strength of the torque-biasing differential inside the NV242, but there are slip-yoke eliminator kits available from JB Conversions and Tom Wood’s Custom Drive Shafts.

NV261 and NV263
The NV261 and NV263 (HD and XHD) found in the ’01-’07 GM Duramax diesel-powered trucks have a flaw known as pump rub. The internal oil pump floats inside the rear housing of the transfer case. Over time, one of the five indexing tabs on the pump housing wears through the factory anti-rattle clip and into the transfer case housing, eventually causing an oil leak. Merchant Automotive (merchant-automotive.com) and Offroad Design have developed inexpensive kits to prevent pump rub on the NV261 and NV263. The kits work on virtually any four-wheel-drive GM built from 1998 to 2007, which includes the NV136, NV146, NV236, and NV246 transfer case models.

For those performing solid-axle swaps, Offroad Design offers heavy-duty 32-spline front output slip-yoke eliminator kits for the ’99-’07 GM NV261, NV263, and NV246.

NV271 and NV273
These monster transfer cases can be found in 3/4-ton and up GM, Dodge, and Ford 4x4s. If you’re breaking the NV271 or NV273, you likely have other driveline problems that you don’t know about, which caused the failure in the first place. The NV271 and NV273 will split in half and shoot their guts out if you install too long of a front driveshaft that jackhammers the front output as the suspension compresses. However, it’s more common for them to catastrophically fail when the CV in the front driveshaft runs dry and locks up. There really is no way to protect the NV271 and NV273 from this type of damage, other than regular driveshaft inspection and proper driveshaft maintenance.

’79-’95 Toyota Hilux/4Runner
If you have seen an older Toyota 4x4 creeping along the trail at a snail’s pace, then you have likely seen the off-road potential of the ’79-’95 Toyota transfer cases. Companies such as Marlin Crawler (marlincrawler.com) specialize in Toyota transfer case improvements. Most notable are the 2.28:1 low range dual-case systems, but adding the Marlin Crawler 4.70:1 ratio low range gears to one of the range boxes provides more gearing options and increases the versatility of your 4x4 in a variety of off-road conditions.

A common failure point for high-horse and big-tire applications is at the transfer case inputs, especially between doubled up range boxes. To combat this, Marlin Crawler offers the Total Spline 23-spline heavy-duty transfer case input gear to replace the factory 21-spline unit. The 4.70:1 aftermarket low range gears are available with a 21- or 23-spline input. Marlin Crawler also offers heavy-duty 30-spline chromoly front and rear transfer case outputs for the early Toyota ’cases.

New Process and New Venture ID

New Process/New Venture transfer cases can be found in many of the most popular 4x4 brands. Ever wonder what all the NP and NV nomenclature means or what the difference is between an NV231 and an NV273? Let us help you.

Every NV and NP transfer case came with a round identification tag riveted to the backside. We’ll use the NV241 and NP241 as an example here. Obviously, the NV stands for New Venture and an NP stands for New Process. The drivetrain company name changed several times. Anyway, the first number in NV242 (2 in this case) indicates it is a two-speed transfer case with a high and low range. The second number indicates the strength rating (a 4 is stronger than a 3 for example). The third and final number is a bit more complicated. It indicates the type of differential (if any) and the shifting mechanism used. A 1 a means it’s a part-time transfer case; a 2 indicates it has full- and part-time modes; a 3 indicates it is electronically shifted; a 4 means it’s all-wheel-drive; a 5 means it has a Torsen-style differential; a 6 identifies it as having a computer-controlled multi-plate wet clutch; a 7 indicates a GeroDisc differential; and a 9 means it has a viscous coupling. Also, each vehicle manufacturer gets a different letter at the end of the transfer case model number. For example, you might see a tag on the transfer case with a NV241C. The C identifies the NV241 as a Chevy model. A GM would indicate a GM application; a J would indicate a Jeep transfer case; a D would indicate a Dodge transfer case; and so on. Other variations include HD (heavy-duty) and XHD versions, which will have an increased GVWR, most commonly found on diesel and other heavy-duty applications. Obviously, the earlier NP transfer cases like the NP203, NP205, NP208, and others don’t follow this newer identification system.

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