Greg Lenderink's 1971 Jeep CJ-5 Project

What Is this?

This page will detail the ongoing project of our '71 Jeep CJ-5. The plan is to try to retain the factory body look, but build a bullet proof, easy to maintain drivetrain that will handle all but the most extreme conditions. I'm not trying to build a competition rockcrawler because I don't want that long a wheelbase nor do I want to use axles that wide.

What are the primary components?

The plan is to build a drivetrain consisting of a Cummins B3.9 4 cylinder diesel, a Dodge NV-4500 5-speed transmission, an Advance Adapters Atlas II" 4.3:1 Extreme low transfer case & custom reverse-cut Dana 44 axles (built by me) connected via triangulated 4-link leading-arm & trailing-arm suspensions.

OK. How are you going to fit all that into a CJ-5 wheelbase?

I'll be the first to admit, this will be a challenge. The CJ-5 wheelbase of 81" doesn't allow for a very long drivetrain. The NV-4500 is what makes this tough, but I can't think of another transmission, with an overdrive, that will be able to stand up behind the Cummins. My plan is to move the engine, radiator & intercooler as far forward as possible & then to move the axles forward and rearward as much as necessary to make things fit. The reverse-cut Dana 44's are part of the plan. Dana 60's would be nice, but the 60 pinion nose is almost 4" longer than the Dana 44's & I'll need that extra 4" for the driveshafts.

The Objective

My objective is to build a bullet-proof 4x4 mostly suited to rock crawling & snow bashing, but also adept at other types of 4 wheeling while still maintaining good streetability. This is a tall order & cannot be obtained in a stock vehicle. This will not be a "trailer queen" nor will it be a canyon carver. Two of my biggest issues w/ many 4x4s is the disregard for fuel mileage & the inability to be driven as a grocery getter. Goofy leafed vehicles are especially scary to drive anywhere but a straight line or in granny low on a trail. That, coupled w/ a high horsepower 'Vette motor under the hood can make things really dicey. It also seems that many of these 4x4s simply cannot carry enough fuel for a full day of 4 wheeling or must stop every 150 miles on the highway to tank up.

I don't plan to drive cross country in this Jeep, but would like to be able to drive across the state, take the kids to school or put 300+ miles under my belt w/o a lot of hoopla.

My other pet peeve is having to fix my vehicle after every outing. I want to be able to take this Jeep 4 wheeling on a day trip or take it to Moab or New Mexico for a week of hardcore stuff w/o having to fix it every other day. This is also a tall order, but I believe the following plan will meet all these requirements.

The Plan

Remove the entire original drivetrain

Swap in Cummins B3.9 4-cylinder turbo diesel engine w/ an intercooler

Although about the same weight as a big block Chevy, this engine provides vastly superior low RPM torque at the same time giving 30+ mpg mileage & extremely long engine life w/o major modification--perfect for this application.
With minor modifications, ridiculous amounts of torque are available from this engine--in excess of 400-500 ft/lbs.
Diesel engines are great for off-angle & steep incline/decline operation. They are not susceptible to electrical malfunction while fording deep water.
Used B3.9s are readily available & relatively inexpensive
The only real detractions of this engine are it's low governed speed of 2650 RPM & an annoying idle vibration if idle is set too low. The NV4500's 5th gear overdrive coupled w/ 36" tires offset the low governed RPM problem. Also, fitting in an intercooler will be a real challenge, although I don't have to use the original intercooler. I'll just have to get create in its design.

Swap in NV4500 5-speed transmission

No matter how much power or torque is available from the engine, this transmission will stand up to it. A Jeep CJ-5 is relatively light & this tranny is used in Dodge & Chevy 1-ton trucks behind much bigger diesel engines. Breakage here is not an issue.
Getting the right gearing & the right output shaft here is important. A 6.34:1 granny gear is preferable along w/ the Chevy output shaft as it allows a direct bolt up to the Atlas II transfer case.
Using a 5.9 Cummins bellhousing, bearing retainer, bellhousing adapter & clutch should allow this tranny to bolt directly to the B3.9.
The 0.73:1 overdrive is a perfect replacement for a good ole Warn Overdrive originally available this Jeep. It also helps w/ the problem of the low governed B3.9 RPM. This particular Jeep didn't have the O/D option.

Swap in Advance Adapters' Atlas II Transfer Case w/ 4.33:1 reduction

Build custom reverse-cut Dana 44 axles front & rear (Dana 60s are too heavy & the pinion nose is too long for this application)
- Acquire 2 '78-'79 Ford Bronco front differential housings (have both)
- Front Axle
  - Use shortened axle tubes & closed knuckles from '69 Chevy 4x4 front Dana 44 (already have)
  - Closed knuckle tubes are being used because u-joints in closed knuckle axles have better longevity & require less maintenance than u-joints in open knuckle front axles provided the proper lubricant is used & the front end is built correctly.
  - Modify the closed knuckles to accept Torx thin headed Grade 8 bolts threaded from inside
  - These ¾ ton knuckles must be machined slightly at each bolt hole to provide a flats for the bolt heads to rest against
  - Use '76-'81 Jeep CJ or Scout II front disc calipers, mounts, & spindles (need)
  - PowerLok limited-slip or ARB air locker differential. This Jeep needs to be driveable on & off road in all conditions
- Rear axle
- Retain 5"x5½" wheel lug pattern
- Build both axles w/ integrated trusses over the top of each axle to facilitate strength w/o losing ground clearance. Will be integrated into the leading arm/trailing arm suspension.

Custom built suspension
- Utilize custom leading arm/trailing arm coil spring type suspension, similar to Jeep Wrangler/Grand Cherokee type suspension, but using longer adjustable length arms w/ heavy duty Heim joints on each end. The lower arms will parallel the frame rails & the upper arms will be triangulated to eliminate the need for a panhard rod.
- Utilize adjustable coil over shock spring packs in order to provide maximum wheel travel while maintaining sufficient tire contact pressure. The idea is to build a flexible suspension w/o going overboard to obtain excessive wheel travel. Supporting the behemoth 4 cyl diesel will be interesting.
- Move rear axle back 4"-5" to make room for the drivetrain & improve departure angles.
- Move front axle forward 2"