1991 Jeep Wrangler YJ Buildup - Project Old SchoolPosted in How To on May 17, 2007 Comment (0)
We had a person ask us, "What's 'old school' about building a Jeep with just about every part being new or high-tech?"
If this person had read the first installment a little more carefully, we named this project as we did because we're building it in a neighbor's garage as we used to in the old days, and we're keeping the leaf springs under the axle, just like the old days. This person also commented that our neighbor had all the tools and equipment of a high-end fabrication shop. Wow! Did you know that you too can have a high-end fabrication shop if you own a torch, a small MIG welder, and a set of tools? We're glad, though, that people are reading and making comments, whether positive or negative.
Our '91 Jeep YJ Wrangler sat idle for a time while we resolved some transmission issues. We told you in our first installment that we planned on mating a GM 4L60E automatic behind the Hemi, via an Advance Adapters adapter. Our prototype adapter needed some modification, so we had to go in another direction in order to get our project finished in a timely manner. That direction was trading our Advance Adapters 4L60E for an Advance Adapters 727 TorqueFlite automatic. According to everything we had heard, the 727 would bolt right up to the Hemi with no adapter necessary. In fact, the sales brochure for the stand-alone MPI 5.7 Hemi says you can bolt it right in to your older Challenger, Road Runner, etc., that had a small-block A-pattern block in them. Yes, the bolt patterns match. No, it's not that easy.
Most of the older Mopar engines were externally balanced. The new Hemi is internally balanced, so it requires a zero- or neutral-balance torque converter and flexplate. Also, the older torque converters had an asymmetrical bolt pattern, so they won't bolt up to the Hemi's symmetrical, 90-degree-bolt-pattern flexplate. No problem, just use an older Mopar flexplate. You know the one, it looks like a cross. Oops, the small-block flexplate fits a six-bolt pattern on the crank and the Hemi is an eight-bolt pattern. Still no problem, right? The old Mopar big-block Hemi and 440 Six-Pack had an eight-bolt pattern and we can use one of those flexplates. Nope, wrong again. The new Hemi's eight-bolt pattern doesn't match the old pattern. Mopar says in its instructions to use the flexplate and converter from a new Ram pickup. Right. The new Ram converter has a computer-controlled lockup. The whole reason to use the stand-alone Hemi is to install it in older vehicles that aren't computer-controlled. The new Hemi has no transmission programming in its small brain, and our old Jeep (or Challenger, Road Runner, etc.) has no computer to control the transmission and torque converter.
As we were learning all this, it seemed like a problem. The solution was simple though. We had Advance Adapters' transmission experts build a nonlockup, neutral-balance torque converter with the late-model, 90-degree, symmetrical bolt pattern and a fairly low 1,800-rpm stall. This torque converter bolts right up to the flexplate that comes on the Hemi. We forgot to tell the shop that we had a ring gear on the flexplate, so it sent a torque converter with the ring gear welded to it like the older Mopar ones were. No problem, the tooth count is the same as the existing flexplate, so we bolted it on anyway. Even though having the two ring gears isn't hurting anything, we suggest getting a converter built sans ring gear if you do this swap. To complete the package, we installed a Mopar factory starter used on a late 360 Magnum motor.
So, the 727 is on the engine, and the Atlas is on the back of the tranny. We stripped everything out of the engine compartment and got the whole assembly slid between the framerails. We were surprised to find that the exhaust manifolds that came with the Hemi will work! The half of the Tera motor mounts that bolt to the block work, but our friend Eric Maughan fabricated new frame mounts. We're now in the process of fitting everything and building a crossmember/skidplate. Once everything's finally installed, we're going to use a Lokar shifter and throttle and kickdown cables from Advance Adapters.
We replaced the YJ steering box with a new box from PSC, along with the company's excellent ram assist and power-steering pump. Tom at PSC said that the OE power-steering pump for the Hemi is one of the finest available today. PSC makes it even better with its modifications. We had the company send us a box that has more road feel, as well as a smaller ram. This will give us good highway manners while still providing plenty of steering power off-road. HM Engineering sent us four precision high-misalignment rod ends and threaded inserts so we can build a beefy tie rod and drag link.
The stock YJ power brake booster will be inadequate for the four-wheel disc brakes we now have. We acquired a dual-diaphragm booster and master cylinder kit from Master Power Brakes. The Master Power Brakes kit includes everything needed, even a new proportioning valve, and is a very nice looking, quality product. We've used MP Brakes' products before and know they work well.
It was time to deal with the fuel tank. The old tank was replaced with a new Gen-Right aluminum Crawler Extreme tank. The Crawler Extreme allows the axle to move back 4 inches and also sits 1 inch higher than the stock tank. The large Currie Iron Jock now has room to move up and back. Gen-Right's tanks swap in easily to whatever vehicle application for which the tank is built. All vents and holes are OE-spec. We thought it wise to replace the fuel pump in our 150,000-mile Wrangler, so we ordered a new pump from Bosch, which has a fuel-pump application for just about every vehicle on the planet. We modified the in-tank fuel module to use the Bosch pump and installed it in our new Gen-Right tank.
It was slow going as we waded through our transmission, torque-converter, and flexplate issues. Now that we've figured out what works, it will be easy going for any of you who want to swap in a stand-alone Hemi in your non-computer-controlled vehicle. The solution was as easy as having a torque converter built for the application. The rest of the project is back on track, and we should have the Jeep running in the next installment.
4 Wheel Drive Hardware
Don's Professional Collision Repair
Gen-Right Off Road
Interco Tire Corp
Master Power Brakes
Mickey Thompson Performance Tires & Wheels
Mountain Off-Road Ent. (MORE)
OMF Performance Products
Pro Comp Suspension
Tuffy Security Products
Walker Evans Racing
West Motor Co