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.
Our T-case was a goner. However,...
Our T-case was a goner. However, we had a buddy who had parted-out a couple Wagoneers for their axles. He took the time to grab the T-cases as well. After sitting on them for a couple of years he just needed them gone, so we hauled them away for free. We pulled the Mile Marker part-time kit from our old case and used the free case with the tightest chain for our rebuild.
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.
Teardown is quick and easy....
Teardown is quick and easy. The only special tool required is a pair of good snap-ring pliers. Thomas removed our shifter cover, vacuum-operated shift mechanism, popped off the low-range unit, and gunned off the rear driveshaft yoke so the case halves could be separated.
There’s a small plug in the...
There’s a small plug in the bottom of the Quadra-Trac case through which you can insert a small screwdriver to check chain stretch. If there’s more than 1/2- to 3/4-inch of slop, you should replace the chain. Our chain had over 3 inches of stretch, and under heavy load we could feel the chain skipping teeth on the gears.
The tooth skipping wasn’t...
The tooth skipping wasn’t the first thing that tipped us off to a problem, however. We noticed a hole in the side of our case. It turns out that one of the keepers in the cheap China chain had snapped and acted like a chainsaw tooth, slicing through the soft aluminum case and letting all the ATF pour out as the vehicle was driven.
Thomas dismantled our good...
Thomas dismantled our good spare case and along with the Mile Marker part-time conversion kit from our wasted original case and gave everything a ride in MIT’s industrial degreaser. The parts come out squeaky clean and ready for a quality rebuild using a DT Components seal kit. Normally bearings aren’t needed, but MIT had extra parts on hand in case we ran into any unusable components.
On the left is the stock Quadra-Trac...
On the left is the stock Quadra-Trac differential assembly, output shaft, and shift collar. On the right is the Mile Marker part-time kit that replaces these components and makes true two-wheel-drive possible. Once the Mile Marker kit is installed, you can run straight ATF without the need for the fancy TLC-1 fluid.
The Quadra-Trac differential...
The Quadra-Trac differential is rebuildable. By removing eight bolts on each side, you get easy access to the clutch packs within. If you’re looking for a dirt-simple, full-time four wheel drive system for inclement-weather towing, off-road racing, or winter driving, it’s actually a pretty good system.
All Quadra-Trac rear output...
All Quadra-Trac rear output shafts are 10-spline, but Sugg tells us he sees either 10- or 26-spline front output shafts with no apparent rhyme or reason as to year or application. Our donor case had a 10-spline output and our original case had a 26-spline. By the way, the stock 10-spline 1310 CV yoke will work on the front or rear of Spicer 18 and Dana 20 T-cases.
MIT used to rebuild a ton...
MIT used to rebuild a ton of these back in the day and even though it had been about 10 years since he rebuilt a Quadra-Trac, Sugg didn’t miss a beat. After inspecting the common wear points of our low-range assembly like the sun gears, main shaft, and internal splines, he reassembled our low-range assembly and then drove new output seals into our case. Then, the rear output shaft was fitted into the Mile Marker-supplied shift collar and installed in the case. Finally, the plastic thrust washer from the part-time kit is laid in place.
After the front yoke was installed,...
After the front yoke was installed, Sugg used the low-range box to keep the case sitting level and installed the chain over the drive gears. Both are lowered into the case as an assembly. Then, a new O-ring was fitted into the case and the case halves bolted together.
The rear yoke is installed...
The rear yoke is installed and then the four-pinion planetary assembly for the low-range unit is set in place. Another new O-ring is laid in the case bore and the low range assembly is carefully fit over the planetary sun gears.
With the planetary all buttoned...
With the planetary all buttoned up, a new O-ring was slid onto the shifter rod, then the shift fork and assembly were reassembled in the case. This vacuum-operated shift mechanism is often the source of problems. Cracked or broken vacuum lines are common external causes, or the sliding shaft can get gummed up with clutch pack debris circulating through the T-case. Be careful not to lose the E-clips that hold the fork in place during the reassembly process.
If your Quadra-Trac isn’t...
If your Quadra-Trac isn’t shifting properly, Sugg suggests first removing the shift switch and adding a thin steel shim washer under it. Sometimes alleviating the excess pressure from the indicator switch off the shift rod will get the T-case shifting well again.