Quadra-Trac Transfercase Rebuild
Keeping Jeep’s Most-Maligned T-case
Everybody loves to hate the Quadra-Trac. It’s like gum on the bottom of your shoe, diarrhea, and fat Kirstie Alley all rolled into one. Jeep introduced the BW1339 Quadra-Trac to its full-size pickups, Cherokees, and Wagoneers in 1973 and then plugged it into the ’76-’79 CJ-7 platform for good measure. It was always found behind the TH400 auto transmission, so if you got a manual gearbox you escaped the humiliation. But why the bad rap? In most instances it’s a pretty durable unit with (for its time) very advanced O-ring seals and a clutch-type differential for full-time four-wheel drive. Its biggest problem, in short, was the people who owned ’em.
The clutch pack inside the differential requires special gear lube with a friction modifier for the limited slip differential clutch packs. It’s no longer for sale at your local Jeep dealership but Crown Automotive offers it through its vendors under PN TLC-1. If you ignore this and fill with regular ATF or straight 30W, the clutch packs wear out and chatter. It also wasn’t unheard of for owners to add locking hubs to the front axles in an effort to improve fuel economy. Despite the fact Mile Marker has a part-time conversion kit for these transfer cases, many were run in two-wheel drive with the stock differential in place. The result was fried clutch packs in short order. Finally, the chain is a wearable component. Over time it would stretch and required replacing. When available, genuine Jeep and good USA-made Morse-brand chains were expensive, so cheapskates bought and installed chains made in China. And you guessed it—the Chinese chains break and wear at an alarming rate.
We had a Quadra-Trac in our ’78 Cherokee that needed some help. It sported the optional low-range assembly and had a Mile Marker part-time conversion that was installed back in the mid-’90s. Unfortunately, the shop that did the conversion pocketed the good Morse chain included in the Mile Marker kit and installed a China-brand chain that eventually killed our case. We scrounged a couple good cases as spares from a buddy and brought the whole arsenal down to Mechanically Inclined Technicians in El Cajon, California, where Andy Thomas and owner Jeff Sugg took the cream of our crop to make one good Quadra-Trac. In addition to engine conversions and other custom work, MIT deals with dozens of axle, transmission, and T-case rebuilds a week, and Sugg and Thomas knew all the tricks in dealing with these cases. Now our Cherokee has a fully operational four-wheel-drive system for the first time in years.