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11 Best Transfer Cases - Case Closed

Posted in How To: Transmission Drivetrain on October 1, 2007
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The transfer case is the heart of the four-wheel-drive system in your rig. Naturally, this means that you want one that offers outstanding function and exceptional dependability. But with an array of transfer cases available, there is a question that begs to be answered. Which have proven themselves to be rugged and durable?

To answer that question, the staff here at Four Wheeler met around the ol' roundtable of discussion (which is actually square) and created a list of our 11 current favorites. Surprisingly, there wasn't much debate because we all chose basically the same units. In this list (which is in no particular order), you'll find some familiar models that are proven performers in the 'wheeling world. You'll also see a few relative newcomers that take transfer-case technology and beef to a whole new level. One thing all of these transfer cases have in common is that we'd bolt any one of them under our rigs. As a matter of fact, some of us have.

Why it's cool: Over 30 years. That's the production span of the Model 18, and that is an incredible lifespan that speaks volumes about its reliability. This cast-iron, offset-drive, geardriven, two-speed 'case is found in '40-'71 Jeep vehicles as well as some International trucks. Our own Tech Editor Sean Holman has this 'case in his '51 Willys.

There are a few versions of the Model 18, with the most desirable being the "large case" version found in '66-'71 vehicles behind the Buick V-6 engine with the T-86 or T-14 transmission. We've seen the Model 18 subjected to more power than it was originally designed for, and for the most part it handles the power without complaint. However, because the Model 18 is a side-drive 'case, the intermediate gear is always under load. The result is that the bearings and intermediate shaft are prone to wear.

How you can get one: These are very hard-to-find units. However, Novak Conversions has had some luck in procuring these units for customers. If you already have one, they offer complete rebuild kits for the Model 18 and they offer a special hardened intermediate shaft that holds up extremely well to wear. High Impact Transmission & Gear also has rebuilt units and rebuild parts. Advance Adapters offers adapters to mount the Model 18 to a variety of manual and automatic transmissions.

Why it's cool: The NP205's ruggedness is truly legendary. An indicator of this is the fact that 16 of the 30 Top Truck Challenge competitors from 2004 to 2006 have had a 205 integrated into their rigs in some fashion.

The 205 is a geardriven unit that has come standard in many Dodge, Ford, GM, and International trucks. It has a low-range ratio of 1.96:1 and an overall length of approximately 14 inches. Be aware that there are many different versions of this unit with a variety of input shaft and bolt pattern configurations. There are also "married" and "divorced" versions. Gobs of aftermarket upgrades are available to make the 205 even better, including twin sticks, a Klune underdrive, and the popular Off Road Design "Doubler," which melds the gearbox section of an NP203 to a complete 205 case to create a 4.0:1 'case. If you're hunting junkyards for a 205, Stephen Watson of ORD notes that it's important to get all of the parts for the unit-even the adapter, as these can run $250-$300 by themselves.

How you can get one: Off Road Design offers a wide range of rebuild kits and parts as well as completely rebuilt 205s with a new 32-spline front output shaft and a fixed-yoke rear output shaft. Vince and the team at 4xHeaven can also set you up with rebuild parts, or they can rebuild your 205 for you.

Why it's cool: One of our editors had a Scout and he swears he couldn't kill its Dana 20, though he unwittingly tried many times. The cast-iron-cased, geardriven, 2.0:1 low-range Dana 20 was found in a variety of vehicles including Jeeps, Chevys, and Fords in addition to the aforementioned IHs. It was a follow-up to the Dana/Spicer 18 and some parts interchanged. Unlike the Dana 18, the 20 had a more direct method of drive in high-range. The Jeep and Scout Dana 20s were the most similar of the bunch.

How you can get one: The folks over at High Impact Transmission & Gear have rebuilt Dana 20s waiting for a home, and they also have a wide range of rebuild parts. 4xHeaven can also help by rebuilding your Dana 20 or by providing rebuild parts.

Why it's cool: The folks over at Advance Adapters created a legend with the Atlas II transfer case. Again, we can use Top Truck Challenge as an indicator of how tough these 'cases are. The Atlas is the second-most popular transfer case with TTC competitors, with around 30 percent of the field running one in their rigs from 2004 to 2006. The rugged one-piece case is made from 356-T6 heat-treated aluminum alloy, so it can take a beating. It houses strong helical-cut gears supported by needle bearings that are precision-matched to strong 8620 shafts. These shafts are supported by large taper bearing sets. The Atlas II is available with 11 different input-shaft splines and two front output shafts; either 26- or 32-spline. That's not all. We love the way the 'case is available in six different low-range ratios. Our favorite is 4.3:1 because it's a do-it-all ratio. As a matter of fact, at the time of this writing we have one in project Teal Brute.

How you can get one: The team at Drivetrain Warehouse can hook you up. You can also order an Atlas II directly from Advance Adapters.

Why it's cool: A direct descendent of the Dana/Spicer 18 and the Dana 20, the 300 is a strong 'case with helical-cut low-range gears (unlike the Dana 20). This translates to quiet low-range operation. This 'case was found primarily in '80-'86 Jeep CJs and in the '80 Scout, though they do not share the same bolt pattern. The 300 features geardrive and a cast-iron case and weighs in at around 85 pounds. The 300 also offers 2.62:1 low-range gearing as opposed to the Dana 20's 2.0:1. The Dana 300 was the last cast-iron, geardrive transfer case installed in a factory Jeep.

How you can get one: High Impact Transmission & Gear offers rebuilt units as well as a full range of rebuild parts. 4xHeaven can rebuild your 300 for you or be a parts source. Novak Conversions offers a variety of adapters which allow the 300 to be bolted to a variety of automatic and manual transmissions.

Why it's cool: The 2.62:1 low-range 13-56 was used primarily in '87-'96 Ford F-Series and Bronco trucks. Even though it has an aluminum housing and chaindrive, it is extremely durable and Ford used it behind a wide variety of powerplants including the 7.3L diesel and the 460ci V-8 gas engines with great success. Normal wear items include bearings and the chain. If the 13-56 has an Achilles' heel, it is the oil pump, which can break loose and rotate on the drive, causing a loss of lubrication. Some pre-empt this problem by running a sheetmetal screw through the pump and into the housing. The folks over at Jeff's Bronco Graveyard also note that because the 13-56 mounts only to the transmission, it is susceptible to axlewrap damage. They recommend stabilizing the case or controlling axlewrap.

How you can get one: Give the folks at Bronco Graveyard a shout. They have rebuilt 13-56s as well as a full line of standard hard parts. By the time you read this, they'll have a slip-yoke eliminator kit available for Ford pickups too.

Why it's cool: Let's see ... cast 356 alloy-aluminum T6 hardened housing, helical-cut ASTM alloy 8620 heat-treated gears, ASTM alloy 8620 heat-treated shafts, 32-spline output shafts, high-quality tapered roller bearings, and more than 60 3/8-16 stainless-steel socket-head cap screws. Need we say more? OK, we will. The Monster Box is clockable in 4-degree increments up to 360 degrees, Jeep TJ-specific shifters are available, and there are a large number of yoke and flange options. Speaking of options, you can get a parking brake, vehicle speed sensor, and a 4WD light. All of these cool things and two low-range gears to choose from on the trail. Ain't life grand?

How you can get one: Contact Stak 4x4

Why it's cool: The Marlin Crawler has evolved over the years, and today it's a household name among Toyota fans. We like the Dual Ultimate Crawler because it mates the super-tough MC07 dual adapter plate to a rear 'case with 4.70:1 gears. This setup offers 20 forward and four reverse gear combinations. The Ultimate Crawler fits '79-'95 geardriven transfer case applications with the four- and five-speed transmission. It is also available with 4.0:1 or 4.97:1 gears in either 21- or 23-spline configurations. It's worth noting that the MC07 adapter features a 5209W double-row maximum-capacity 32-ball bearing, cage roller bearing, oversized billet mainshaft, a new bearing retention system, and increased oiling capacity. In other words, it's tough.

How you can get one: You can get this setup directly from Marlin Crawler in Fresno, California.

Why it's cool: The standard NP241 was a good, but not great, transfer case. They were typically used in '87-and-up Jeep, Dodge, and Chevrolet V-8 applications. They use 2.72:1 planetary reduction gears for low-range and chaindrive for the front output. Typically they use a slip-yoke rear output shaft. We like the beefier NP241HD found in Dodge 3/4- and 1-ton trucks with the V-10 or Cummins diesel engines. Some of its upgraded features include a stronger front output chain that is 1/4 inch wider than the non-HD chain and a more durable six-pinion planetary instead of the non-HD three-pinion planetary.

How you can get one: This is a hard transfer case to find, but when we spoke with the folks at High Gear Transmission in Memphis, they had a unit in stock. If you already have an NP241HD, the team at 4xHeaven can get you parts or they can rebuild it for you in-house.

Why it's cool: If you're into rockcrawling or rock racing, there's a good chance you've heard about the Lovell 357. If not, we'll tell you about it, because this thing is super trick. First off, the "357" moniker refers to its reduction ratio of 3.57:1. This single-speed, geardriven unit was designed for competition and features a premium-grade aluminum alloy housing and high-strength steel gears and shafts rated to withstand loads in excess of 11,000 lb-ft of torque. It weighs 115 pounds, is 9.22 inches in length, 18.23 inches in width, and has a height of 9.98 inches. It offers 32-spline output shafts and your choice of 23-, 27-, or 32-spline input shafts. Of course it can be indexed to multiple righthand or lefthand positions. The 357's most unique feature is that it uses pneumatic pressure to actuate clutches for the front and rear outputs. This allows instant engagement and disengagement under any conditions, without gear binding, via toggle switches. A small 68ci compressed air tank will cycle the 'case 500 to 1,000 times, and it can be engaged at virtually any rpm. The unit is also a direct bolt-in replacement for the Atlas II.

How you can get one: The 357 can be ordered directly from Lovell Engineering.

Why it's cool: This case was originally found under 2.5-ton military 6x6s. It's a monster unit that weighs approximately 400 pounds. The housing is cast iron and it's geardriven. It sports a 1.98:1 low-range ratio and is a divorced unit. Shifting is via air, and the experts at Boyce Equipment tell us that it only requires 36 psi. Over the years, this case was adopted by some monster-truck drivers looking for a unit that would hold up to the abuse of 66-inch tires. Even today, those with rigs running 2.5-ton Rockwells have found the T-136-27 to be the hot ticket for durability. It's important to note that there was an earlier version of the unit that was very similar visually. It was simply referred to as the T-136. This unit is not desirable because it has mechanical shift and an undependable front drive sprag.

How you can get one: Contact Boyce Equipment in Utah.


Advance Adapters
Paso Robles, CA 93446
Drivetrain Warehouse
Compton, CA 90220
Boyce Equipment
Ogden, UT 84401
Marlin Crawler
Fresno, CA 93703
Novak Conversions
Logan, UT 84321
Stak 4x4
El Paso, TX 79936
Bronco Graveyard
High Gear Transmission
Lovell Engineering

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