By the late ’50s, the Willys Wagon was starting to look long in the tooth. The American public wanted bigger vehicles with more creature comforts, and the Jeep Corporation wasn’t dumb—it started development of what was to become the SJ platform in the early ’60s. Debuting for the ’63 model year with a revolutionary overhead cam inline-six, the Wagoneer was the most luxurious 4x4 on the market. By 1965, the Gladiator pickup joined the lineup that was to run largely unchanged for the two and half decades.
If we are really honest with ourselves, these Jeeps are really more mid-sized when compared to offerings from other companies, but the size makes them better off-road than other companies’ fullsize vehicles—and this might account for their continued popularity. Whatever the case is, many of them came from the factory with V-8s, automatic transmissions, long wheelbases, and decent axles. All of which make them a great choice for a build platform.
The six-cylinders just aren’t going to cut it in the mud. Even fuel-injected they don’t have the power to pull these bigger Jeeps. If you’ve got one, look into a V-8 swap. If you’ve got a V-8 with emissions junk on it, figure a way out to legally get rid of it and get more power. Long-tube headers, a mid- to high-rise intake with a four-barrel carburetor, and cam can really light up the AMC V-8s. Whether a wagon or a truck, you are going to want to cut the fenders to open up the wheel openings. Not only does it allow for bigger tires, but in the sticky stuff, the wheel openings pack with mud. Then you end up blipping the throttle to clear the mud from the tires, only to pick up more mud in the tires from your inner wheelwells—which can lead to going nowhere fast.
Unless you are making some massive horsepower, the factory axles will hold up to even mildly built factory V-8s just fine. And, if all you are doing is bogging in a field, there really isn’t a reason to toss the closed-knuckle front axle. You might wanna pull the spare out from under the back of the Jeep, though, because that thing attracts a ton of mud. If you have a Cherokee or pickup with trimmed flares, you can run 33s with no lift and 35s or 37s with a 4-inch lift. Wagoneers have to cut a bit more sheetmetal and worry about the rear door opening.
In the rocks, the biggest problems are the rockers and the ass end of the body. The trucks have it worse than the wagons, but both can suffer. The cheapest way is to bend some tube for the rockers and rear corners. If you want to get aggressive, you can chop the rockers and rear corners and get 4-6 inches more ground clearance but then you will want to reinforce the sheetmetal under the doors. You will want some kind of belly pan, too. Basically, any factory engine will work, and many of them came with the Motorcraft carburetor, which does well at angles. If it doesn’t have the Motorcraft on it, a Q-jet is an inexpensive swap, or pick from any of the many aftermarket fuel injection setups out there.
Most of the transmissions in these things are okay, but the combination of T-case low ranges and axle gears usually isn’t adequate for crawling. The Dana 20 only has a 2:1 low range but the aftermarket has kits to make it lower. The later NP208 has a decent 2.61:1 low range but the axles were often geared in the 2-3:1 range. So for the earlier Jeeps, first go with lower T-case gearing, for the later ones (’80-and-up), look at putting lower axle gears in it. If you’ve got any of the Borg-Warner ’cases, you might want to consider swapping them out. If you’ve got a closed-knuckle front axle, you might want to swap to an open-knuckle setup for improved turning radius.
Stripping is the order of the day here. If you don’t mind taking time and have the ability, pulling the doors and tailgate off will make for a completely different Jeep in the sand. If you get it light enough, the six-cylinders can pull you through but the V-8s are going to be a lot more fun. The FSJs are wide enough and the factory springs stiff enough that they tend to sidehill really well. Put a spool or automatic locker out back and shoot some roost. These things have a long enough wheelbase that either is fine in day-to-day use. The sheetmetal transmission pan of the automatic and the aluminum T-cases won’t even handle one shot. While many of the bellies of these Jeeps are flat, we’ve seen dented pans and cracked ’cases from cresting a dune. You might want to spend some time building a belly skid.
As for axles, most of the stock axles work. The open-knuckle/closed knuckle thing is kind of a wash. With the ’74-newer open knuckle axle, sand can find its way down the tube and start wreaking havoc with the inner seals. With the ’73-older closed knuckle, it can work its way past the knuckle seal and tends to cake up on inner ball, destroying the seal. So, where do you want your repairs to be after extensive sand blasting? If you have a stock engine, cut the flares and squeeze some 33s in there. If you are putting more power down, a small lift and 35s would work. But 37s are going to start testing those stock axles.