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Mad Rooster Off-Road
Planetary Crawlerbox
By Ben Wellner
When planning the build up of my
1992 Wrangler, I decided that one of the key features I wanted was deep crawler
gearing. As I looked for a product to fit my needs, and my budget, I found many
affordable options for Toyota and Suzuki owners, but nothing available for my
Jeep. Then I discoverd Mad Rooster Off-Roads new Plantetary Crawlerbox adapter.
Mad Rooster's kit, based on the very common NP231 transfer case was perfect
for my buildup. Combining the Planetary Crawlerbox with my AX-15 transmission,
Dana 300 transfer case and 5.86 gears gives me a crawl ratio of 160:1, just
what I was looking for.
 Mad
Rooster's Crawlerbox is a surprisingly simple concept. It uses the 2.72:1 planetary
gears and 1/2 of the housing from the NP231 and turns it into a crawler. At
only 7.5" long the crawler is very compact and light weight. Combined with my
Dana 300, the complete package is 17.5" long overall. Compare that to a stock
NP231 at 18.5" and the crawler/Dana 300 combo is very attractive, even for a
Wrangler's short 94" wheelbase. The Crawlerbox can also be bolted to a 23 spline
NP231 case for those with a longer wheelbase, or the crawler/Dana 300 combo
can be flipped for use with a driver side differential.
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Included in the kit is the adapter
plate, a rotation ring, and a through hardened 4340 chrome moly steel mainshaft.
Mad Rooster also includes all the necessary hardware and some basic instructions
to help you install your new Crawlerbox.
The first step in installing the crawler is to split the NP231 in half.
This isn't as difficult as it sounds. First I removed the nut on the front
output. Then I removed the 8 bolts holding the 2 halves together and pried
between the halves to break the silicone seal. Once the seal was broken
I was able to pull the rear half of the case off. All the parts that I didn't
need stayed attached to the rear half, and the good stuff remained on the
workbench in front of me. |
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The next task is to cut off
the front output. I bolted the adapter plate to what was left of the NP231
and began cutting with a hacksaw. The case was very easy to cut, and in
a few minutes I was left with what was to become the Crawlerbox. |
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Now that the output is gone,
there is a hole left that must be sealed. I headed off to the local fabrication
shop to have a 3/8" aluminum plate welded over the hole. A few hours and
$20 later I had my Crawler back and ready to be installed. |
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Next up is to bolt the rotation
ring to the Dana 300. The rotation ring is used to set the clock the transfer
case to the desired angle. The adapter plate is then bolted to the clocking
ring at the appropriate angle for your installation. |
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There are 2 more steps before
installing the crawler. First is to shorten the shift rod. I needed to shorten
the rod to 7 1/8", the chop saw and grinder made short work of the task
and I was ready to move on. Next on the list is setting the endplay of the
mainshaft. This is accomplished by installing a shim and test fitting the
Dana 300 & adapter plate to the Crawlerbox. You add shims to the mainshaft
until their is a gap between the plate and the Crawlerbox. Then remove one
shim and you are good to go. With the endplay set, I was ready to install
the crawler. With plenty of RTV to seal the adapter, I bolted the 231 to
the adapter plate. |
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The Crawlerbox is installed
into the Jeep just like the NP231 that it once was. Simply bolted to the
transmission. Though the stock transmission mount is still used, Mad Rooster
recommends adding a support to crawler adapter to help support the extra
weight. I simply welded a mount to the adapter plate and bolted it to the
skidplate with a bushing. I also notched the skid plate to clear the Dana
300. |
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In a Wrangler, the stock shift
linkage can be hooked up to the crawlerbox. If you don't have that option,
a simple shift linkage can be fabricated. |
Driving with the Crawlerbox to a
whole new experience for me. At 160:1 it is virtually impossible to stall the
engine. Where I was used to using momentum, I can now let the Jeep idle up the
obstacle with complete control. I also have many gear options available. I can
use the stock low range for faster sections of trail and for sand and snow wheeling.
Mad Rooster's Planetary Crawlerbox is one of the best modifications I have made
to my Jeep.
Contact
Mad Rooster Off-Road
Phil Porter
Madera, CA
559-232-5566
madroosterfab@yahoo.com
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