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Jp’s Guide To Jeep Transfer Cases

Open Transfer Case
Robin Stover | Writer
Posted January 1, 2012
Photographers: Christian Hazel

Transfer Station

Do all Jeep T-cases look the same to you? In the junkyard, did you ever mistake a Quadra-Trac for a rare aluminum Spicer 18? Are you as lost as Pee-wee Herman at a rodeo when it comes to identifying what T-case your Jeep left the factory with? Don’t know if your factory case is a keeper or junk; or where to get upgrades for it? If so, this guide may be worth keeping around in your garage or shop. We wish we had enough space to go into every little detail on every unit built, but we don’t. So, instead we picked those we thought were most important and put together this guide.

The Odd Ones
The following cases are less common and less popular for various reasons. These oddballs are not ideal for swaps due to their complexity or a problematic vacuum engagement system. All can be identified by a round tag on the rear portion of the case.

NV247J/ NP249: These cases came in ’93-’98 ZJ (NV249 Quadra-Trac) and ’99-’04 WJ (NV247J Quadra-Trac II). Each has a full-time 4WD system that automatically biased torque between front and rear axles. For the ’99 WJ, the NP247 “Quadra-Drive II” was introduced. The system used a gerotor pump to proportion torque through an internal clutch setup. When coupled with Jeep’s Vari-Loc axles (WJ only) the entire system was called Quadra-Drive instead of Quadra-Trac II. Unfortunately, NV247s can be problematic and expensive to repair and are not recommended as swap candidates.

NP219: Found in ’80-’82 full-size Cherokees and Wagoneers, the NP219 is based off the NP208. Comprised of a full-time 4WD chain-drive system with an aluminum case, the major difference between the NP219 and other models in the NP208 family is the lack of a vacuum-operated center differential.

NP228 and NP229: Found in ’80-’84 full-size Cherokees and Wagoneers, the NP228 and NP229 were based on the NP208 and feature the same exterior shell and chain-driven 4WD system. The only difference between the two is found in 4-Hi. On the NP228 the center differential will remain open in 4-Hi while the NP229 has a limited-slip differential to assist with high-range traction. Both units have differentials that will lock 100-percent when 4-Lo is selected and both feature a vacuum-operated center differential.

Spicer 18
The Spicer 18 is lightweight and employs a compact design that fits within the tight confines of smaller vehicles.

Found in: Bantam BRC, Willys MA and MB, Ford GP and GPW, CJ-2, CJ-2A, CJ-3A, CJ-3B, M-38, M38A1, CJ-5, CJ-6, and the FC-150 and FC-170.

Identifying it: It is the only cast-iron Jeep T-case with both outputs on the passenger side. The PTO is on the back of the case and drives directly off the input gear. This unique arrangement allows fitment of PTO accessories or planetary overdrive units.

Variations: Thirty years of production allowed the Spicer 18 to see much refinement. Five major versions exist; early ’41-’45, ’45-’46; ’46-’55; ’55-’71; and ’66-’71. Early versions had a 1.97:1 low range, while the latter versions featured a 2.43:1 or 2.46:1 low range. With each new version came improvements to the size of intermediate shaft as well as upgrades to bearing design. Most early Spicer 18s came with twin-stick shifters from the factory, but many later models also employed single-stick shifters. The most sought-after version is found behind Buick V-6-powered CJs sporting T-86 or T-14 transmissions. This variant sports a 4.00-inch locating bore and a sturdier housing more akin to the Dana 20.

Pros/Cons: It’s strong for its size and the inline front and rear outputs simplify off-road driving by aligning the lowest hanging parts of the undercarriage—which is especially handy for rockcrawling scenarios. The downfall to the Spicer 18 is found in the design of the case. Under some extreme circumstances the case is known to crack between the intermediate shaft bore, the case bottom opening, or the PTO window. Due to the offset rear output design, some inherent power loss is unavoidable since all the engine power must transfer through the intermediate gear.

Aftermarket: Novak offers a billet-aluminum inspection pan and PTO cover and TeraFlex sells a 3.15:1 low-range gearsets Overdrive choices include genuine vintage Warn or Husky (Warn knock-off); modern Saturn Overdrive by Advance Adapters; or ATV Mfg. Overdrive by ATV Manufacturing.


Advance Adapters
Paso Robles, CA 93446
Murray, UT 84107
Tom Wood's Custom Driveshafts
Ogden, UT 84404
JB Conversions
Sulphur, LA 70664
Novak Conversions
Logan, UT 84321
Mile Marker
Pompano Beach, FL
Mile Marker
ATV Manufacturing
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