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 interchangable, 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.
