Spicer/Dana 18 Transfer Case

The Spicer/Dana 18 is a gear driven transfer case that comes in 5 slightly different variations. The early version of the Dana 18 had a 27 tooth drive gear and 3/4" intermediate shaft and 1.98:1 low. The second generation Dana 18 came with a 26 tooth input gear and 3/4" intermediate shaft and 2.42:1 low. The third generation Dana 18 came with a 26 tooth input gear and 1-1/8" intermediate shaft and 2.42:1 low. The fourth generation Dana 18, uses a 26 tooth input gear, 1-1/4" intermediate shaft, and 2.42:1 low range. The fifth generation Dana 18 uses a 29 tooth input gear, 1-1/4" intermediate shaft, used a larger input hole, the same case used in the Dana 20, and has a 2.46:1 low range. The big hole input is about 4" in diameter where as the small hole input is about 3" in diameter. All Dana 18 cases are cast iron.

The small hole Dana 18s are interchangeable, but the input gear must match the transfer case. The big hole Dana 18 can be bolted on a transmission that was originally coupled with a Dana 20 and visa-versa. All Dana 20 and Dana 18 input gears are 6 spline except ones used with the 10 spline version of the T-14 transmission. All Dana 18s and Dana 20s use the 5 bolt "Texas" bolt pattern.

All Dana 18s have front and rear outputs offset to the passenger side. Trucks built with a Dana 18 have a rear axle that is offset to the passenger side. Most other transfer cases used in Jeeps have a centered rear output that couples directly with the input shaft so that no gears are turning when in high range 2WD. The Dana 18 always has gears turning which makes it wear faster, noisier, and not quite as strong as some other Jeep transfer cases. It is still a strong unit, just not as strong as some other Jeep transfer cases.

A unique feature of the the Dana 18 is the overdrive, developed by Warn, that attaches in the PTO port in the back. There are also PTO attachments that can be used to drive winches, generators, welders, assorted farm implements, and about anything else you can imagine that might accept PTO input.

Some photos courtesy Daniel Regan:

	Front view of small hole Spicer/Dana 18.
	Rear view of small hole Spicer/Dana 18 with PTO plate removed.

 

Usage

The Spicer/Dana 18 was used on the first CJs and their military counter parts until 1971. It was also used on all other trucks until around 1965. During the late 60s, many of the larger trucks were built with the Dana 20. The MBs and GPWs used in WWII used the 27 tooth Dana 18. The CJ-2A up to serial number #24196 in early 1946 used the 26 tooth, 3/4" intermediate shaft Dana 18. CJ-2As after than and the CJ-3A and CJ-3B (to serial number 54-12506) use the 26 tooth input gear and 1-1/8" intermediate shaft. The Dana 18 with a 1 1/4" intermediate shaft and 26 tooth input gear was used on the CJ-3B (after serial number 54-12506), CJ-5, CJ-5A, CJ-6, and CJ-6A. The big hole Dana 18 was used with Jeeps equipped with the Dauntless V6 engine. It is not clear if the big hole Dana 18 was ever used with the 134 I4 and T-90 combination, they probably continued to use the small hole Dana 18 with the T-90. The big hole Dana 18 uses the same cast iron case that is used on the Dana 20.

Contributors

Thanks to Fred Coldwell for the first generation Spicer 18 CJ-2A serial number information.