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Building a Bulletproof NP205

131 0505 Tran 01 Z
Rick Péwé | Writer
Posted May 5, 2005

Tips and tricks for the toughest transfer case available.

The venerable NP205 transfer case has a reputation for being as tough as a rock, but the truth is--it's even tougher. Just let this cast-iron beauty slam down on a trail boulder and watch the chips scatter.

If that isn't a tough enough reason for using this unit on your wheeler, we don't know what is. Small and relatively compact, the stock NP205's only serious drawback is the menial 1.96 low-range reduction, but future mods and aftermarket doublers can take care of that issue. We've seen this geardriven case used and abused by massive amounts of big-block torque and monster tires and run to death with water in the oil, and we've been constantly amazed at its durability. In fact, we doubt this unit, properly built and maintained, could be seriously hurt.

The 205 came in GM, Ford, Dodge, and International trucks as far back as 1969, and it was produced in GM trucks until the mid '80s when the NP208 finally replaced it in all applications except for cab and chassis trucks, which kept the 205 until '91. The venerable 205 was made in lefthand drops for Ford and righthand drops for the rest, as well as remote and married versions, and late-GM applications even had a slip-yoke rear housing. Different input and output shafts were used through the years, but the core case design and center cluster gear remained the same on all units. Identifying an NP205 is relatively easy: It has a cast-iron case and center idler shaft with a nut on the front and a three-bolt cover on the rear, is about 12 inches long, has a center rear output, and usually has an ID tag above the front output shaft.

The super-tough NP205 case is found on many '70s and '80s vehicles from all manufacturers. We chose a GM unit with the drop on the right side, and Performance Gear & Axle cleaned and checked the bores on the case before we started. This casting number (C-99404) on the left identified that we had a '70-'77 GM case with direct mounting, which is almost exactly what we wanted. The case to the right is a mid-'70s Ford with direct mounting and a lefthand drop. Notice the eight-bolt racetrack type pattern on the GM case, which was used from '71 to '85, before the common six-bolt round pattern was introduced.

We went to Performance Gear & Axle in Mississippi to build a unit to our unique specifications, since we have no intentions of leaving our 205 stock. In fact, we had an NP208, so Performance Gear & Axle pulled a 205 out of stock just for this rebuild. Performance Gear & Axle has a great reputation for unique driveline combos, even mating a Clark five-speed to a Dana 300 transfer case or an NP205 with its own line of adapters. In fact, the company even offers reproduced factory style adapters for the hard-to-find TH400- and TH350-to-NP205, and even one for the never-produced 700R4. The company even has a special bearing available to run a lefthand drop behind Chevy and Dodge trannies for those of you with your front diff on the left side. Owner Ed Hotard sat down with us to go over the many variations found in the 205 over the years, and came up with a killer recipe just for our uses.

Since our application for this bulletproof 205 project is our '85 GMC 2500 3/4-ton with a TH400 tranny and an NP208, we decided to go for maximum strength and adaptability. Our present TH400 had a cracked case, and we knew we could sell the functional 208, so we decided to rebuild the TH400 with a short output shaft for a stock TH400-205 application. This is the shortest and strongest combo and required a minimum of modifications. However, we felt that the 1.96 gear ratio in Low was a bit on the wussy side, so an Off Road Design Doubler was thrown into the mix. The Doubler is essentially just an NP203 low-range reduction unit, and is designed to bolt between the transmission and transfer case. This doubles the gear reduction and gives us many more options for wheeling. We also wanted the twin-stick conversion for shifting the 205, which Off Road Design offers as well. Our new plan was to use the factory TH400-to-NP203 output shaft in the tranny so that the Doubler would bolt right in. Then the adapter from Off Road Design would bolt into the NP205 from Performance Gear & Axle. Strong, simple, and usable is what we wanted, and this would work great. We even upgraded the front output shaft for maximum durability. Check out how we put the transfer case together with this assortment of parts, and wait for a future issue to see the trick TH400 and Doubler install.

Case Variations
The NP205 has numerous variations, only a few of which we show here. Different input-shaft diameters in male or female varieties, left or right drops, adapter bolt patterns or remote styles, and strange stuff we've never seen--yet all combine to provide a mystical aura for the hallowed 205. The most common varieties are the early-model GM (A) with eight-bolt racetrack pattern (round six-bolt front mounting pattern shown here), the Ford remote mounted with a fixed yoke on the input shaft (B), and the late-style GM with a slip-yoke rear output (C). Even input bearing diameters vary, so measure to see which one you have.


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