One-off Jeep J20 with an LS3, 37s and linked suspension

This 1981 Jeep J20 is Sam Kovac’s daily. You see, Sam is a self-confessed sucker for a good project.

His usual method is to find a half-finished build that has had a lot of the difficult work already completed, then he comes in, snaps it up, finishes it off for a fraction of what it would’ve cost him if he started from scratch, then sells it for a tidy little profit. Wash, rinse and repeat.

That was the plan with this old school Jeep truck too, which he found as a rolling shell with no driveline (other than the old engine) or wiring. The thing was, Sam kind of liked this one, different to the usual Patrols and Cruisers, and has held onto it for a lot longer than he usually does, daily driving it for the past couple of years as well as blasting up the sand on the islands and beaches around SEQ… as you would, given the lengths he’s gone to, and the sheer fun of piloting a 370kW full-size rig over the dunes.

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Oh, in case you weren’t already aware, Jeep utes have been around since the 40s, and were called the Gladiator in the US (sorry JL owners, your Gladiator is far from the original).

Built to compete with the Fords, Dodges and Chevys of the 60s, 70s and 80s, the Jeeps were a solid unit overall, but ultimately couldn’t hang with the sheer sales numbers of the Big Three, and eventually were discontinued by the late 80s.

But back to Sam’s J20, which has everything most folks could want in a 4X4: power, comfort and off-road ability by the imperial gallon. If you can’t see yourself punting this down the beach, V8 singing, big rubber floating over the soft sections, enjoying every second of it, you may need to seek counselling. Or you’re just grumpy. Either way, keep your chin up, champ.

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It'd be rude not to

When you’re building a classic full-size American truck, it’d be downright impolite not to throw a big, corn-fed hunk of Uncle Sam’s finest engine in between the rails.

Luckily, Sam was raised right, so he shoehorned in a crate LS3. For those unfamiliar with arguably the finest engine series out of the GM stable, the LSX engines are pushrod, fuel injected V8s.

The LS3 is a hefty 6.2L and is capable of some massive numbers when worked. Other than a GM hot cam and tune though, Sam is more than happy with the relatively stock 370kW and 620Nm output figures.

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Being no stranger to the mighty LS, with an LS1 79 Cruiser, an LS1 dual-cab HiLux and an LS2 Luxy under his belt, Sam had the engine in without too many dramas. However, as with so many conversions, getting it mounted was the easy part.

The six-speed auto was sourced from a Chevrolet Silverado, so bolted right up, however the transmission’s computer and the engine’s computer decided they didn’t like each other and refused to talk.

After a frustrating hunt trying to find someone local to sort out the software incompatibility, Sam latched onto Ultimate Conversion Wiring down in NSW, who he sent both ECU and TCM to. Within a few minutes they had the problem solved, the control units were back in the vehicle and Sam could focus on tuning, which he did himself with HP Tuners software.

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Interestingly, the J20 retains the stock Jeep transfer case, which is bolted to the Silverado ’box via a Novak adapter. Sam reckons it’s held up so far, but it’s a rare beast these days so if it ever does let go, he says he’ll replace it with a much easier to find Patrol transfer case.

The transfer case crossmember is made from 12mm steel and is butch enough to jack the entire vehicle up from, while also serving as a bit of underbody protection. Both tailshafts also needed to be lengthened/shortened to accommodate the new powertrain dimensions.

Making the big V8 sound like it should is the exhaust that measures a gnarly 4-inches in diameter from the headers back. Keeping things cool is the largest alloy radiator that Sam could fit, and a pair of Delta PAG thermo fans.

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Leaf springs? Yeah, nah

Solid axles and leaf springs. A combo that’s been around forever, and still works, as long as you don’t mind a rough ride and limited flex (without some serious modifications).

While the J20 came standard with the old beams and semi-ellipticals, this one has been not only modified but modernised with a suspension and diff set-up more commonly seen on an Ultra4 off-roader than a daily driven ute.

The rear axle is a 10.5-inch Stirling from an F-250 that’s been fitted with a Yukon selectable Zip Locker for supplying guaranteed drive to the 37x13.5x20 Mickey T Baja MTZs, that are fitted up to drool-worthy 20-inch TrailReady alloy beadlock rims.

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The rear suspension is a triangulated four-link supported by Kings 2.5 remote-res 12-inch coilovers and Kings hydro-bumps.

Meanwhile, the front diff is a Zip-locked Currie RockJock 60, an ultra-strong aftermarket fabricated housing that uses heavy duty axle shafts and the bombproof Dana 60 centre. King 2.5 remote-res 14-inch coilovers supply the compression and rebound while the three-link and Panhard arrangement allows maximum flex without compromising handling.

If you were to take your own rig to a suspension specialist and said “give me the best of everything” you’d likely get something pretty close to this back.

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Old dog, new tricks

Despite the classic appearance, there’s actually a bunch of modern touches on the J20.

The front fenders, for example, are moulded fiberglass, and there’s LED lighting at either end to bring after-dark visibility forward a few decades.

While the interior is largely stock, with the original bench seat and trim, Sam has included a Pioneer stereo and a Power Tune digital dash, which relays everything from the engine’s CANBUS system. The 7-inch screen is housed in a custom 3D-printed housing that Sam did himself.

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In fact, Sam has 3D modelled and printed a bunch of stuff, including the under-dash AC evaporator unit.

Anything that’s been printed in prototype form by Sam is left in red, then when it’s deemed to be suitable for use it gets sent off to be printed in black UV resistant material. Pretty nifty if you ask us.

Sam also made the custom buttons on the steering wheel, which are his take on paddle shifting – one button for shifting up, one for shifting down. Apparently it works a treat, too. All up, it’s an incredibly impressive and unique build and has to be one of the coolest dailies we’ve seen in quite a while.

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What's next?

Sam did mention that for now he’s pretty happy blasting the J20 up and down the coast and enjoying the hell out of what he’s achieved.

With that said, he’s pumped to get started on a new project, so don’t be surprised if you see the big Jeep on the market before long. If you’re keen on a linked and coil-overed American truck with power for days, reach out and we can put you in touch with Sam.