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1978 Jeep J-20 Flatbed - Jeep Encyclopedia

Posted in Features on November 25, 2014
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The Jeep light truck debuted in 1947 as a 1-ton 4x4. It was reasonably up to date then but remained in developmental stasis through the ’50s, growing ever more dated until 1962 when the J-Series Gladiator line debuted. The J-Series trucks were a big step ahead of the first-generation trucks and on par with the rest of the market. Kaiser Jeep was never big enough to be cutting edge very often but managed to keep the SJ (Senior Jeep) fresh and attractive through an almost 15-year tenure owning the Jeep marque.

AMC bought the Jeep line in 1970 and was a bit better poised to capitalize on the J-Series trucks. It certainly filled that gaping truck void in its model lineup, and AMC had a better and bigger dealer network than Kaiser. AMC was perhaps a little more “hip” and better at the marketing game as well. The company immediately switched the Jeep line over to its engines, a particular bonus in the big Jeeps. The AMC buyout could largely be considered a plus for the Jeep line in general.

Kaiser Jeep had started the Gladiator truck line out with a bazillion wheelbase and GVW configurations, as well as a plethora of commercial options and factory-installed special bodies. That was pretty standard for the era, but times change. Even before the AMC takeover, that was being dialed back and the efficiency-minded AMC dialed it back even more. When 1978 rolled around, the lineup was down to three basic models: Model 25, 45, and 46, with a number of trim and special packages available for each to spruce them up.

Walter Zimmerer is a flatbed kind of guy. The truck was originally configured as a pickup but Walter found one of the original-style flatbeds and installed it to make his J-truck a little different. In this era, a flatbed would have only been available from the factory for fleet orders. You could order a J-truck as a cab-and-chassis, and the dealer or someone else could install a flatbed as an accessory.

The Model 25 was the short wheelbase 1⁄2-ton (118.7 inches) J-10 with a 6-foot bed. The Model 45 was a long wheelbase (130.7 inches) J-10 1⁄2-ton. Both J-10s had a 6,025-pound GVW rating but could be beefed-up with optional heavy-duty springs. The Model 46 J-20 was a long wheelbase configuration but divided into three optional GVWs: 6,800, 7,600 and 8,400 pounds.

In the J-10 line, the legendary 258ci inline-six was a base option (except in smoggy California, where the 360ci two-barrel V-8 was the base) and a 360ci two-barrel (175 hp), 360ci four-barrel (195 hp), and 401ci four-barrel (210 hp) were the V-8 options. The ’78 model year would be the last in which the 401ci thumper was on the options list.

This 360ci two-barrel V-8 was the standard engine for the J-20. It cranked out 175 hp at 4,000 rpm and 285 lb-ft of torque at 2,400 rpm. In the base configuration, it would have a four-speed T-18 and a Dana 20 behind it. The original owner ordered it with the automatic, which came with Quadra-Trac, whether you wanted it or not. The AMC engines used Motorcraft two or four-barrel carbs, and both were pretty decent units.

The available transmissions included the base Warner three-speed T-15A (inline-six and 360ci two-barrel V-8 engines only.) A T-18 wide-ratio four-speed (standard on the 360ci four-barrel V-8) was the popular middle option, and the stout GM TH-400 was the automatic. Unfortunately, the automatic only came with Quadra-Trac full-time four-wheel drive verses the part-time Dana 20 on the manuals. The automatic and Quadra-Trac were the only combination available with the 401ci V-8. All the trucks used a Dana 44 front axle (either 3,200 or 3,500-pound rated). The J-10s used a Dana 44 rear axle rated at 3,500 pounds, but the J-20s had a 5,500-pound Dana 60 full-floater.

By 1978, the old Thiftside (stepside) bed option was no longer available and all trucks had the Townside bed. Trim levels ranged from the base model to the Custom, which had had a better interior and more geegaws on the outside. The 10-4, Honcho, and Golden Eagle packages were built on the Custom and added various decal kits, tire and wheel packages, and a few extra convenience options. They were only available on the J-10 models. The familiar two-tone paint was still a popular option in this era, so that and the Custom trim were top of the line for a ’78 J-20, according to the Jeep Data Book.

This truck was ordered with the optional bucket seats in the beige Wellington vinyl and these are the original ones. The carpet is original, too. Comfort wise, this was the top of the line for the J-Truck of this era. The only alteration from stock is the aftermarket radio. If you are wondering where the low-range lever is, it’s under the seat on Quadra-Trac trucks. Quadra-Trac came with or without a low range, but the single-speed Quadra-Trac is seldom seen in trucks. The vacuum-operated center differential lock control was in the glove compartment. The Trac-Lok limited slip was not available with Quadra-Trac.

At the time it was shot, this ’78 J-20 belonged to Walter Zimmerer, who was the second owner, and it was only showing only about 25,000 miles. It had spent most of its life plowing snow, but since that snow was on a long private drive that was unsalted, it didn’t acquire the usual destructive patina. It remains largely in original condition with under 30,000 miles. Only 3,169 J-20s were built in 1978, so it’s also relatively rare. Pristine examples like this are even more rare.

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