The name Art Morrison Enterprises (AME) has been synonymous with hand-crafted, custom chassis for decades. The company’s offerings have suspended many show-winning rides. The company’s 3G 1960 Corvette highlighted the handling characteristics of the AME chassis so well it was crowned with the Grand Turismo Award at SEMA in 2006. It was also included in the video game so millions of enthusiasts could enjoy driving the car. The company’s latest endeavor continues its ground-breaking, evolutionary spirit as the talented staff at AME set out to create the first 4×4 chassis of its kind.
As the rolling business card for AME’s new 4×4 chassis, the truck is almost too clean to take off-roading. But, of course, that is where this chassis was designed to really shine!
As a completely new, custom-built design, this new AME 4×4 chassis for 1973-’87 Chevrolet and GMC trucks and Blazers began with a strict set of rules in mind. The company sought to give this new chassis an amazing amount of travel for off-roading but also wanted to provide the necessary street manners so you could drive to work comfortably. Already known for their street and track manners, this new aspect opened up a whole new world for the engineers at AME.
The entire chassis has been engineered in-house. Even the front and rear axle housings (left) and steering knuckles are fabricated at AME. The 4x4 chassis can be ordered with either five- or eight-lug bearing assemblies (right) to suit customer's needs. Note that AME's red truck has been upgraded with a shiny, new set of Wilwood brakes featuring six-piston front and four-piston rear calipers.
“The ultimate 4×4 chassis would be a good way to describe it,” says Matt Jones, President of AME. “Pre-runners are high-speed desert racers and rock crawlers are crazy articulate and durable — this is a blend of the two with street manners in mind. Our chassis has to drive excellently on the freeway to earn the Morrison name. It’s capable of high-speed off-road use and crawling over huge stumps. It can do it all and comfortably drive home without worry of what just broke.”
The Testbed Truck
When building the ultimate 4×4 chassis, it helps to start with a platform that is designed to get out there when the going gets tough. For that, there could be no better testbed than this 1974 GMC 2500 pickup that was a former brush fire truck from Mapleton, Utah. The truck saw use from 1974 until 2022. Even so, when AME purchased it, the truck had only clocked 15,000 miles on the odometer.
The truck was used to fight fires until AME purchased it. As such, it was spartan in amenities, but well-equipped for the intended task.
The 4×4 truck originally came from the factory with a two-barrel, 350 cubic-inch V8 and a super-low first gear. In its new configuration, the truck will use a new Chevrolet L8T engine and a 10-speed transmission. Matt states that all engine configurations will be offered and the transmission mount is adaptable to fit just about any transmission available. This truck uses an Atlas transfer case to split the torque between the front and rear axles. The AME 4×4 chassis can be designed for either an Atlas or the very common NP241 transfer case that was offered in GM vehicles from 1989 through 1999.
Building The Ultimate 4×4 Chassis
The AME staff wanted to build a capable 4×4 chassis that could withstand the rigors of off-roading while retaining the necessary road-handling characteristics to allow for daily street driving. “Solid-axle rigs aren’t known to drive nicely on the street, but they don’t have the complexity, cost, or lack of ground clearance of an independent front suspension setup,” states Jones. AME engineers designed the entire front and rear suspension geometry to control all aspects that affect drivability and durability. The custom-built front and rear axle housings and inner and outer knuckles are totally AME designed and manufactured, allowing the company to increase durability, reduce weight, and improve drivability over OEM designs.
Both the inner and outer steering knuckles for the front axle are custom-fabricated at AME. The outer knuckles are designed to use bolt-on type bearings so you don't have to mess with all the little pieces and setting bearing preload.
Both front and rear wheel bearings are beefy, bolt-on units from a Super Duty truck and are available in either five- or eight-lug versions. The front axle shafts are 35-spline units with aftermarket forged 4130 ends fitted with 1480 U-joints. Rear axles are available in semi-float and full-floating versions.
You can see how much effort goes into fabricating the front axle housing (left and center). The front 35-spline axle shafts (right) are aftermarket forged 4130 using heavy-duty 1480 U-joints. Both front and rear axle housings use a 9-inch-style differential in just about any ratio from 2.50:1 to 6.50:1. This truck uses a 5.38:1 gearset.
The new AME 4×4 chassis offers 12-inches of travel for the front suspension and the rear offers 13-inches of up-and-down motion before hitting the gas-charged bump-stops. AME also offers its 4×4 chassis with conventional foam bump stops for those not needing such niceties. To soften the flow between bump stops and travel straps, a set of Fox coilover shocks keep the ride height stable, no matter the terrain, and AME-designed sway bars keep the bumpers aligned with the horizon in all but the most arduous terrain.
In keeping with the capable 4×4 chassis theme, AME chose the famously stout 6-bolt “Dodge steering box.” Weighing in at 45 pounds, this monster features a huge 40-spline output shaft that is mated to a double-shear Pitman arm created by AME. This modern box provides zero-wandering on the street without excessive effort at the steering wheel. Likewise, the truck already had its first trip into the great outdoors and Matt reports that the steering box worked superbly on some “crazy off-road trails,” even with the 40-inch tires.
The steering has been upgraded thanks to the heavy-duty "six-bolt Dodge box" (left) connected to the double-shear Pitman arm via the 40-spline shaft (right).
For this build, the tires of choice are 40×12.50-17 BF Goodrich Baja KR3 tires on 8.5-inch-wide Trail Ready HD17 wheels. To divide the torque between each of those tires, several differentials are available, including an open differential, TruTrac, Detroit Locker, or an air locker, as used on this truck. The option to unlock the axles allows for improved drivability when not going off-roading.
Blending Modern Capability To A Classic Truck
The AME staff is very passionate about off-roading and set out to build the ultimate 4×4 chassis for its GMC brush truck. The goal was to combine massive 40-inch tires with a modern suspension offering an amazing amount of travel without the truck getting jacked up like so many were back in the ’80s. To fit 40-inch tires with a relatively low ride height, the AME staff had to make some modifications to the truck’s body. Matt reports that a 35-inch-tall tire will fit without any modifications, but they wanted the ultimate 4×4 truck.
The AME engineers built an entire prototype front and rear chassis (left), tying it to the factory frame for field testing before building a complete, new frame. You can see how much travel the new frame offers and how much the body and bed of the truck needed to be trimmed to give room to those massive 40-inch tires (center and right).
With those big 40s all around, each of the wheel openings was widened and raised about 2 inches, and to allow for a more realistic ride height, a notch was cut into the foot-board to give clearance for each front tire to have complete, uninhibited travel.
AME staff made custom front and rear bumpers for the truck. The old light bar was somewhat crude so they made something that looked similar, but with a little more refined appearance. "The whole theme was a slight modernization of an old brush fire truck," says Matt.
The AME staff wanted to keep the utilitarian look of the brush truck and wanted winch mounts and tow hooks in the bumper. It was determined to simply make new bumpers with the necessary bits.
The whole theme was a slight modernization of an old brush fire truck and the staff at AME went to great pains to keep the feel (if not the function) of this fire-fighting pickup. The truck’s body and bed were treated to an entire freshening and the interior was touched up with some modern amenities during the transformation without detracting from the utilitarian feel of the cockpit.
The interior was upgraded with Dakota Digital gauges (left) and Vintage Air's Gen-V A/C (center) while still retaining that spartan, workhorse appearance (right).
The Dakota Digital RTX gauges modernize the data stream while blending with the vintage vibe of the oh-so-’70s dashboard. A Gen-V Vintage Air A/C unit keeps the occupants cool in the summer and warm in the winter. The entire system replaces the truck’s outdated air-conditioning components and delivers superior performance in a smaller package.
A new layer of that fire-engine red paint was applied, along with the requisite gold-leaf lettering and accompanying lights and sirens. This is a fire truck at heart, you know, even if it is retired from its fire-fighting duties. The truck has just finished its transformation and Matt (as well as the entire AME staff) are looking forward to putting some road miles and trails on their newest 4×4 chassis. So far, the overall geometry has provided the necessary road and off-road capabilities with just a slight tweaking of the coilover shocks and compression-stop placement.
The truck will now serve as a daily-driven business card of the company’s new 4×4 chassis so look for it around AME’s hometown of Fife, Washington, and at shows throughout the season. You may even get a glimpse of it out on the open highway, or the backwoods trails. Either way, it’ll look right at home in its intended habitat.
