The Garage > Work In Progress

7 Seater, Rock Crawler, Street Legal on a Budget?

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Mike DeChristopher:
A YJ frame is a rectangular tube 4" x 2.5". There is a short straight section just in front of the rear axle front spring hanger. This is where I've seen most others have stretched the frame. I bought the same size rectangular tube for my patch. I wanted my extension to be undetectable so I chose to make a long tappered wedge cut for my butt joint. The long wedge increases the weld length significantly and should result in less stress concentration. I can always add more metal later if needed. I carefully jigged up the sections and welded it together. I added another factory looking body mount and some rustoleum and you can hardly tell that its not original.

https://goo.gl/photos/XgUinET8vcPgYwcF9

Mike DeChristopher:
Drive line:
The YJ I bought had a 4.0L to an AX-15 with a 231 t-case with 4:56 rears. My yellow CJ has a 90:1 crawl ratio which I really enjoy, so my goal was to at least match that. I considered the following combinations:
AX-15 + NP231 with 4:1 kit gives me 70:1 for $1400
NP 235 + NP 231 gives me 82.5 for $750
NP235 + NP231 with 4:1 kit gives me 122.2 for $2000
SM420 + NP231 gives me 86.6 for $700
SM420 + NP231 with 4:1 kit gives me 128.2 for $2000
AX-15 + Atlas 2 gives me 87:1 for $2400
AX-15 + Atlas 4 gives me 204:1 for $3500
NP 235 + Dana 300 with 4:1 gives me 122.2 for $1900
AX-15 + NP231 + NP231 (doubler) gives me 127:1 for $800
AX-15 + NP205 + NP231 (doubler) gives me 92:1 for $1000

Prices are approximate but include buying used gearbox from craigslist etc (except I already have an SM420) and all new kits/adapters from AA or Novak.

Based on this matrix, I chose the NP231 doubler from Behemoth Drivetrain. The "strong box" mounts between the AX-15 and NP231. It uses the input shaft, bearing and planetary gear set from a donor NP231. It's a little over 8" long and is indexable. I rotated my t-case clock-wise until I achieved a flat belly.

Mike DeChristopher:
With the frame stretch, addition of the t-case double, and tucking the drivetrain up I needed to cut and reweld the spring perches for both rears. The rear axle needed a 31" driveshaft and a CV joint. This was a perfect application for a Cherokee front driveshaft (no length adjustment required).  For the front shaft, I needed 51". This length requires a 3" tube. I shopped around and landed on Tom's Wood. MShar was the same price but Tom's offered a 4" slip yoke. Because I have the shackle reversal I was happy to have the added travel.

Mike DeChristopher:
Putting body back together. I ended up using all of a 4 x 8 sheet of steel to build the floor and sides. The floor is supported by 1" square tube and angle.

https://goo.gl/photos/JrXefiP6TDA4z36F9

Death Wobble:
Did you get any inspiration from someone else's buildup, or is this all your own concept?  Good luck with it, sounds like it'll be a real attention-getter when it's done.

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