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1989 Jeep YJ Wrangler - Bah-Hum-Mog

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Harry Wagner | Writer
Posted March 1, 2010

Humvee-Wheeled, Mog-Axled YJ

During the last decade we have seen an explosion of TJs on the trails. It isn't surprising, given the torquey factory fuel-injected engines, optional rear Dana 44 axles, and incredibly flexible coil suspensions. If you are going to tear out all of these components and add a V-8 and 1-ton axles, though, it doesn't make sense to buy a TJ unless perhaps you are fond of the car-like dash. Brett Burgard decided to purchase an '89 YJ and use the money he saved on the initial investment to create the Jeep of his dreams.

Chassis
The YJ features a strong, boxed frame unlike the previous CJ frames, which were notorious for rotting and ripping off shackle mounts. The spring hangers were removed from the frame to make way for the custom coil suspension that uses 16-inch-travel Pro Comp ES9000 shocks and Rubicon Express coil springs frenched into the front frame horns and mounted inboard of the frame in the rear. The front of the frame was removed forward of the spring buckets and replaced with 2x4-inch, 0.250-wall rectangular tubing that serves as an air tank in conjunction with the converted York air conditioning compressor mounted on the engine. The front suspension uses a three-link with one upper on the driver side and a panhard bar to control lateral movement. The rear suspension uses a four-link with triangulated uppers to control side-to-side movement. All of the suspension links are constructed from 2-inch, 0.3125-wall DOM tubing and run 1.25-inch shank 1-inch bore QA1 chromoly rod ends on the lowers and .875-inch shank .750-inch bore QA1s on the uppers. The front axle was pushed forward 12 inches and the rear moved back 10 inches to create a 114-inch wheelbase.

Drivetrain
It was necessary to push the front axle that far forward in order for the long-pinion Unimog 404 portal axle to clear the oil pan. The rear axle is a matching Unimog 404 portal. These axles feature 2.13:1 gear reduction hubs and 3.54 gears in the differential for 7.56:1 combined gearing and 21 inches of ground clearance. They also come with air-actuated locking differentials from the factory, meaning that Burgard didn't have to spend any additional money regearing or adding lockers to his new axles. He did add air-actuated switches that are backlit to engage the lockers to confirm when the lockers are on or off. "The biggest cause of breakage on 404 axles is when the locking collar is partially engaged and the teeth strip," Burgard explained.

The axles were not the only thing to be swapped out; the entire factory drivetrain was replaced, from the carbureted 4.2L engine to five-speed tranny and NP231 T-case. Burgard did not shed any tears when tossing these parts in the dumpster, since the new engine is a 5.0L V-8 from a Ford Mustang. The engine is mated to an NP435 four-speed manual transmission with a 6.69 First gear, which required no expensive adapters to connect because it was a factory Ford application. Similarly, a gear-driven, cast-iron NP205 transfer case was bolted to the back of the NP435, although a twin-stick conversion was performed on the transfer case to allow 2WD Low operation. The transfer case routes power through shortened Bronco driveshafts that use 1350 U-joints. Burgard had to do machine work on the portal axles to accept driveshaft flanges, since in the factory application the Unimog axles use a peculiar torque tube design.

This combination produces a crawl ratio of 99:1, even with the paltry 1.96:1 low range of the stout NP205. The gearing is enough to allow the 42-inch Super Swamper IROKs to idle across the boulder patches. The IROKs are mounted on three-piece HUMVEE combat rims that have been recentered and converted to match the 6x205mm Unimog bolt pattern. The tires are steered by a '79 F-150 steering box that is aided by a 1.5x8-inch-stroke hydraulic ram. The box and ram are connected to the Mog axle with a 1.75-inch, 0.250-wall DOM drag link and tie rod fitted with 3/4-inch QA1 chromoly rod ends.

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