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Frame
Every project has
to start somewhere, and with a vehicle this old it usually begins with some intense cleaning.
The 1970 CJ-5 Renegade platform came as a rolling chassis with engine, axles, suspension, steering, wheels and tires
installed. This greatly simplified inspection and cleaning since no disassembly
was required. So after plugging all the “holes” in the engine, I
fired up the pressure washer to remove as much dirt and grime as possible. This
CJ was a southern vehicle, and it had a peculiar red clay coating much of the frame that defied the pressure washer. I’ll finish cleaning and prepping the frame later in the build. For now, I was able to thoroughly inspect the frame and found it to be in excellent condition. The C-channel design of the frame rails contributes to the lack of serious rust issues; water and mud do
not get trapped as in the later CJ’s boxed frame rails. I plan to weld
in frame plates at stress points and possibly additional cross braces to add to the strength of the frame.
Sitting astride the front frame rails and bumper is a homemade winch mounting
plate with a fabricated roller fairlead. Constructed of 1/2" steel plate, this ugly beast was securely but crudely
welded together. I'll use a cut-off wheel and die grinder to remove it from the frame. I plan to remove the
stock front bumper and replace it with something that's heavy-duty with an integrated winch mount. However, I'll have
to wait until I've converted to the manual Saginaw steering - the mounting location of the conversion steering box will dictate
the bumper's mounting method/location.
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Steering
The Ross Cam & Lever steering system was used on CJs from '46-'71.
While functional and effective for its time, it has some distinct disadvantages when compared to the modern Saginaw steering
systems used in later Jeep vehicles. The Ross system relies on a manual steering box (mounted to the frame below the
firewall) and a complex mix of bellcranks, pivot points, and linkages that allows for excessive play and wandering.
The multiple pivot points are wear items that frequently need to be rebuilt or replaced.
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The Saginaw steering gearboxes, introduced to the Jeep line in 1972, have
proven themselves to be extremely rugged and durable. Add to that the simpler steering linkage design of later CJs that
use a single tie rod and a draglink, and the benefits are clear. Tighter steering control with much more durable components
translates to better control both on-road and off. Reduced routine maintenance and repair is also a nice benefit.
Note the Ross system's multiple pivot points (arrows) in the picture.
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Front Axle
Since I'll be swapping in a later model open-knuckle Dana 30 front axle,
I decided to start with cleaning, prepping and rebuilding the "new" front axle. The axle housing was in good shape overall,
as were the axle shafts, differential carrier, and gears. It was extremely dirty inside the pumpkin and there was quite
a bit of crud in the axle tubes. I powerwashed the outside of the housing, then removed all the components and hosed
down the inside with brake cleaner. I also removed the steering knuckles and began soaking the ball joints in PB
Blaster penetrant. Below you'll find a picture of the Dana 30 axle housing after being powerwashed, followed by pictures
of the cleaned and painted axle housing. A master rebuild kit is on order which will include all new seals, bearings
and shims. New front axle u-joints and upper and lower ball joints will also be installed.
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Transmission
When it came to a transmission for the project, I considered
many different options and finally selected the Muncie SM420. This heavy-duty truck transmission was built by GM and
installed in 1/2, 3/4, 1 and 2-ton trucks, busses, and heavy equipment from 1947 to 1967. The
SM420 is fully synchronized in second through fourth gears, and all gears are helically cut except first and reverse,
which are spur gears. Ratios are as follows: 1st gear = 7.05:1, 2nd gear = 3.6:1, 3rd gear = 1.7:1, 4th gear =
1:1. First is a super-low granny gear that will provide an outstanding crawl ratio for slow speed rocky trails.
(My crawl ratio will be 65:1, calculated as 1st gear 7.05 x low-range 2.46 x axle gears 3.73. For more useful 4x4
math, check out my Resources page.) This will allow me to run 3.73 axle gears for fuel economy and highway cruising without giving up
my crawling ability. The SM420 will marry directly to the Buick 225 V6 bellhousing, simplifying installation.
This is a very compact transmission at only 10.7" in length, perfect for a short wheelbase flattie, although it's no
lightweight with its cast iron construction - it weighs in at 135 lbs! Novak Conversions offers an adapter kit to mate the SM420 to the Model 18 transfer-case. After considering all these factors, my transmission
choice became pretty clear. I even found a transmission online in very good condition for $200 (gotta' love
eBay!).
This is the tranny in its original condition. The outside of the case
had the expected dirt caked to it, but cleaned up easily. Note the PTO access plate on the near side and the rear yoke
that indicates this unit was originally installed in a 2-wheel drive truck. The rear yoke will be removed before installing
the transfer-case adapter for the Model 18.
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I pulled the top plate and to gain access to the internals, then removed
the drain plug. With a bucket under the drain hole, I thoroughly cleaned the interior of the case with brake cleaner
until it drained clear fluid. I was pleasantly surprised to find the main shaft and gears to be in good condition.
The synchros and bearings show normal wear. I may order a minor rebuild kit to freshen up some small parts and seals
while the tranny is out of the vehicle. After cleaning the outside of the case, I sprayed it with several
coats of engine enamel.
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The SM420 is a top loaded, top-shifting transmission with the shift
mechanism located in the "tower" and top plate. This tranny has a 1 1/8" ten spline input shaft and a ten spline
output mainshaft.
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Check back for future installments...
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The front bolt pattern is the consistent GM Muncie / Saginaw four-bolt
pattern as found on GM bellhousings and transmissions from the 1940's through the 1990's. The bellhousing from the Buick
225 V6 will bolt directly to the transmission.
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