The 1970 CJ-5 Renegade came with a late version of the proven Spicer/Dana Model 18 transfer case,
which was introduced in the original Willys MB in 1941. It was the heart of the Jeep
four-wheel drive system and was integral to the "Go Anywhere, Do Anything" capability of the
Jeep. The Model 18 served dutifully in a variety of Jeep vehicles for over 30 years; it was also used
in International Harvester Scout 4x4s. It became legendary due to it's strength, durability, ease of service,
and ability to easily handle V8 power.
Spicer/Dana Model 18 is a cast iron, gear driven, offset-drive (meaning that both front and rear driveshafts are in-line)
transfer case with dual modes (2wd and 4wd) and dual ranges (High and Low). The rear of the case offers a PTO port that
can be used to power aftermarket accessories from winches to farm implements, or it can accommodate popular aftermarket
overdrive units such as those from Warn, Saturn, and Husky. The Model 18 was offered in both single and twin-stick
versions. A common modification for the twin-stick version is to remove the interlock pin, which allows for the
added function of 2wd/Low. The fact that both the front and rear driveshafts are inline means that this transfer case
must be paired with axles that have the differential offset to the passenger side.
If the Model 18 has one
"weakness", it would be the relatively high (numerically low) low-range gear ratio of 2.46:1. While
very respectable, it falls short of the 2.72:1 to 4.0:1 ratios common to late model Jeeps. This can be
corrected, if desired, by the installation of aftermarket low-range gear sets.
There are four civilian iterations
of the Model 18 t-case. Another of the benefits of selecting the 1970 Renegade as the starting point for my project
is that it was equipped with the final civilian version of the Model 18, which benefitted from numerous upgrades
and enhancements. Often referred to as the "large case" version of the Model 18, this version was only found
behind the Dauntless V6 engine with its T86 and T14 transmissions. The case housing was essentially the same as
its successor, the Model 20, which boasted a slightly larger case made with improved casting methods. This version employed
a 1 1/4" intermediate shaft, the largest used in the Model 18, which allowed for increased bearing area. For this
final version, the locating bore was increased from 3 5/32" to 4". A new front output cap was used which employed
a single-stick shift mechanism. I like the added versatility that comes with the addition of 2wd/low-range, so I swapped
in the front output cap and twin-stick shift mechanism from the prior version of the Model 18.
I began with disassembly as captured in the pictures above.
The process is fairly straightforward although it's worth noting that, as with disassembly of most automotive subsystems
containing multiple small parts, it's highly recommended that you separate, bag and label the parts for future reference.
I can't be the only one who has rationalized not taking the time to do so by saying, "I don't need to worry
about that... I'm going to reassemble it tomorrow." Then several weeks later I'm staring down at a pile
of parts thinking, "Now where the heck did this go?" Best intentions notwithstanding, save yourself the headache!
I like to have a diagram or service manual handy so that I can label the parts with the correct name - it's extremely
helpful to have consistent terminology between the instructions and my labeled parts. In this case,
Novak Conversions offers an excellent Rebuilders Guide for the Model 18 complete with an exploded parts diagram.
One item of note: be aware that the quality of the intermediate shaft
is critical. Due to the in-line design of the Model 18, this shaft is not only constantly spinning, but it is under
constant load. Some of the name brand rebuild kits from the common 4x4 retailers contain cheaper, foreign made
intermediate shafts of unsuitable alloys that lack the required hardness. Novak Conversions offers a super-durable shaft made from triple alloy gear steel that will ensure long life for your Model 18 rebuild.
If you enlarge the two pictures below, you can see the detail of the wear on the intermediate shaft to
the right. Also note the shift fork bolts - they are square head bolts with a small hole drilled in the head.
This is provided to allow the bolts to be wired to prevent them from coming loose.
Above you can see the earlier style front output cap with twin-stick
shift provision as I reinstall it on the main case. Note that there are numerous areas where Hi-Tack or a similar gasket
sealer are required during reassembly. In the picture above right, you can see where the roller bearings are installed
in their bore. This can be a little tricky and requires a gentle touch since the bearings are "free" and not
caged, and they must be installed prior to sliding the intermediate shaft into place. In the picture below, you can
see the case with the main gears reinstalled. The subsequent pictures show the painted transfer-case once completed,
including the drum brake backing plate and the pivot arm that the parking brake cable attaches to.
If you're questioning my choice of paint for the transfer-case
(and the transmission), there's a practical reason for it and it has nothing to do with "bling". I selected
the Seymour Hi-Tech Engine Coating for it's durability, but also because the brightness of the chrome metallic finish
will make it easier to identify the source of any leaks. The underside of a Jeep gets plenty dark and dirty
on it's own - the metallic finish will reflect light and make service and maintenance a little easier.
At this point in the build,
I changed direction slightly and decided against the transfer case-mounted parking brake. It seems that a
lot of early Jeep owners report issues with this setup - frequent required adjustments, dirt and mud getting packed
into the drum, ineffective braking action when wet, etc. You can read about the alternative I selected
in the Brakes section.