projects
Project CJ-7
Armoring the Skid Plate
Converting
a Dana 300 Skidplate for a Dana
20
article courtesy of
www.offroaders.com
07/16/2001 update - An ounce of
prevention is worth a few pounds of steel. After hearing stories of mashed
drive trains and flattened cross member skid plates as well as seeing 4x4's go
high center (myself included) and do damage to exposed vital organs, I decided
to take preventative action. My drive train consists if a T-18A bolted up
to a Dana 20. The frame I acquired was from a 1981 CJ-7 which I determined
originally had a Dana 300. Therefore the skid plate was designed for the
Dana 300. My T-18A bolts up to a Dana 20 transfer case which doesn't use
the same bolt hole location as a Dana 300. Also the Dana 20 doesn't hang as low
as a 300. I had 2 options. I could hunt down a Dana 20 skid plate or
modify the Dana 300 skid plate I have to accommodate the Dana 20 and in the
process I could strengthen and armor it. Well... needless to say, I chose
the lather. With a local friend in the business of steel fabrication, I
acquired plenty of scrap steel of various sizes, shapes and gauges all for the
purpose of stock steel for these types of projects. With this skid plate
project I approached it a little differently than a project that would require
lots of pre-planning. The general idea was to not just modify the skid
plate to accommodate the T18A / Dana 20 setup, but to also armor and strengthen
it. So a step by step process of bolting it on, measuring and marking,
followed by cutting and welding was used as opposed to a pre-planned type of
procedure.
The first thing was to bolt the skid plate to the frame with the
engine, transmission and transfer case bolted in. The transfer case side
of the drive train was supported by a floor jack and a hand winch at a height
just above where the transmission mount would contact the skid plate.
After bolting on the skid plate marks were made on the skid
plate where there was contact between the transmission drain plug and the
transmission mount. The idea was to cut out these contact locations to
lower, level and re-enforce these areas.
After cutting out these areas, several pieces of 1/4 inch steel
were cut to fit under an inset area that would eventually support the
transmission's polyurethane mount. Because this steel is located below the
skid plate, it effectively lowers the drive train slightly helping to reduce the
drive shaft angle.
| Another area that require modification was directly below the drain plug of
the transfer case. The originally Dana 300 transfer case needed an extra
few inches because it hung lower than the Dana 20. In this case the Dana
20 didn't need any extra room below the skid plate. So this area of the
skid plate was marked and cut out in a level section. Cutting this area
out was a little tricky. I wanted to have a flat edge on the skid plate to
weld a 1/4 inch steel plate to so I marked the skid plate from the bottom -
level with the lowest part of the skid plate that would remain (in the rear
half) and then ground off little by little to get the 1/4 inch steel as tight as
possible to the skid plate. |
 |
Forward of the skid plate (and partially under the skid plate)
was the underside of the T-18A. The transmissions drain plug was now
exposed because of the removal of some of the skid plate. 2 pieces of 3/8
inch steel combined with a large 1/4 inch steel plate extending forward and
wrapping around the forward-most edge of the transmission were welded in to
protect the trans from contact with the larger rocks.
With these pieces fabricated and welded in, attention was turned
to protecting the transmission mount bolts that would hang below the skid
plate. Adding protection to these bolts was just a matter of extending the
forward section of new 1/4 steel back to the bolts and welding it to the new
steel in the inset section of the skid plate.
For extra protection in the event of a high center impact,
gussets were fabricated for the forward edge of the skid plate. These
forward gussets combined with the rear 1/4 plate running completely across the
rear of the skid plate helps to strengthen the plate and enable it to support
more weight preventing possible drive train damage due to a blow from
underneath.
All of the new pieces of steel were then welded in followed by
another test fit and marking of the bolt holes for the transmission mount.
One more test fit with everything bolted up. A few holes were then drilled
in the low areas for drainage. All the welds were coated with a primer
followed by a complete primer of the entire skid plate. For an interesting
effect and to hide those imperfections I used some Plastikote hammered metal
gloss gray finish. A few days of drying and it was ready for the Jeep
frame.
With everything bolted in attention could be directed
towards fabricating a custom anti-torque adapter that bolts from the skid plate
to the passenger side of the transfer case that limits the twisting forces of
the drive train. A simple angle was bolted onto the transfer cases flange
designed for this purpose. A 1/4 inch steel plated with a slight bend in
it was bolted to the skid plate. The angle, steel plate combo were connected
together using a long bolt and rubber bushings from sway bar ends to help
isolate vibration and torque from the drive train.
When it was all said and done, I had added about 30 pounds of
steel to the skid plate but if you're going to armor anything the skid plate
probably should be one of the things that you don't want to neglect.
Hopefully it won't be necessary to test the limits of my design but if I ever
do, I think the several hours of designing and welding will all be worth it.
With the
installation
of a set of
custom drive
shafts the
skid plate
gusset
needed a
small amount
of
trimming.
Using a die
grinder, the
area
outlined in
blue marker
was trimmed
off, them
re-painted.
