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Jeep Guts Built For 40-inch Tires

Posted in How To: Transmission Drivetrain on November 1, 2011
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We worked with GenRight Off Road and managed to shoehorn 40-inch Goodyear MT/Rs under our Wrangler using stock springs and a 1-inch body lift (Part 1, July, ’08, Part 2 Sept. ’08). Then we got ourselves kicked out of our office building with our parking garage LT-1 V-8 swap (Part 1, Sept. ’09, Part 2, Nov. ’09). In the middle of all that, Trasborg moved, picked up a few more derelict Jeeps, and schemed for the perfect combination of transmission and T-case options to make this big-shoed Wrangler do it all.

We are normally manual transmission guys. They have no issues with cooling, we can understand how the things work, and in dire situations you can almost always grab at least one gear and still get home. However, the Caprice cop car the 5.7L V-8 came out of had an automatic, so thanks to California smog laws, the Jeep had to have an automatic. The trick became how to make it live behind a V-8 in a Jeep with big tires.

If that wasn’t enough, we wanted to be able to run in washing-machine-sized rocks, eel-snot-slick clay-based-mud, Abu-Dhabi-height sand dunes, and scenic trails—all with this same Jeep. That means we needed a low-low range, a regular-low range, and a normal 4-Hi setup. So we were looking at either a gear splitter in front of the T-case or a multi-speed transfer case. While the engine provides the power to the Jeep, the transmission and T-case are perhaps the most important components. Pick the wrong tranny, and you are slave to hard shifts or crappy gear ratios. Pick the wrong T-case and you will be cursing about how your low range is either too low or too high. Or, in the worst case, you will grenade the thing because it can’t handle the stress. Choose wisely, young Padawan.

After much research, we decided to send our 4L60E transmission all the way to the right coast and have the experts at Level 10 Performance do the rebuild and modifications. We were originally doubtful that anything could make that slushbox live with what it might be subjected to, but the company had no doubt that they could make it not only survive, but thrive with what we were going to throw at it. In fact, the guys at the company actually kind of laughed when we filled out the spec sheet with our vehicle’s power levels. Apparently, the transmission’s 1,200hp rating is just a little more abusive than what we will be throwing at it.

Level 10 Performance is well known in the race world for its automatic transmissions. The company has been building automatic transmissions for 40 years. When you place the order, there is a simple tech form to fill out with information like vehicle weight, engine power, what you plan on using the vehicle for, and so forth. Level 10 picks the best springs, shift points, and stall of the torque converter for your application.

For the transfer case, we went to Advance Adapters for one of its 4-Speed Atlas ’cases. The Atlas 4-Speed combines a planetary gearset in front of the tried-and-true gear-driven strength of the Atlas II, which will give a dizzying array of gearing options sure to handle whatever we throw this Jeep into. However, our timing sucked and we ended up placing the order at the same time the company decided the ’case needed to be stronger. We were on the very short list for the new-and-improved Atlas 4-Speed and put one of the fledgling few first builds into our Jeep for, ahem, “testing.”

Speaking of torque converters, Level 10 builds its own. The angle and clearance between the vanes is important, as it affects the stall speed of the converter. Often the vanes in factory converters are only attached at one point to save time. Level 10 firmly attaches the vanes to keep them in place for the life of the converter. In lockup converters, the company also uses a better-than-stock friction material to prevent slippage no matter how heavy the drivetrain and tires are.

Once we finished clearing the cobwebs and the green stuff out of the wallet for some sweet bulletproof parts that we couldn’t build ourselves, we hit up Industrial Metal Supply for some steel so we could fabricate the transmission mount, skidplate, and shifter mounts. We also grabbed some junkyard parts to mate our previously manual-transmission-equipped Jeep with our new automatic and multi-speed splitter.

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Lincoln Electric
Cleveland, OH 44117
GenRight Off-Road
Simi Valley, CA 93063
Advance Adapters
Paso Robles, CA 93446
Goodyear Tire & Rubber Co
Akron, OH 44316
Industrial Metal Supply
Irvine, CA 92606
Parts Mike
Level 10 Performance Transmission Systems
Hardyston, NJ 07419
Eau Claire, WA 54703
Wide Open Design

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