Independent front suspension must’ve seemed like impossibly amazing technology to the car-buying public in the mid ’30s. By letting each wheel independently comply with road irregularities it greatly improved traction and ride quality.
While adequate when used in its intended environment along a patchwork of rural highways, these early designs show their age when asked to perform by today’s standards. Their lax caster (specs call for 3/4-degree negative for this ’47 Pontiac) makes steering effortless but robs stability at modern highway speeds. Their high roll centers cause the outside steering tire to roll under in a turn. And because the design doesn’t camber the outside wheel in a turn the tire can’t maintain full contact with the road.
Sure, you can breathe new life into old designs with wider radial tires, by adapting power steering assemblies and disc brakes, altering the uprights to lower the ride height, and even installing dampers that better control the wheels’ motion. But at issue is the cost-to-benefit ratio: those modifications aren’t exactly inexpensive. Nor do they address the root issues like early suspensions’ high roll centers and poor camber curves either.
Swapping the entire suspension for a more sophisticated one usually represents the most effective solution but it’s not without its issues either. A few exceptions withstanding, frames designed for IFS flare out and arch for spring pockets and control-arm mounts.
Two methods exist to update these cars. The subframe method requires cutting the frame at the firewall and grafting to it a portion of frame from a donor vehicle, a job that requires significant fabrication since no two frames come close to matching. The newest ones pushing 30 years old, donor subframes usually require full reconditioning to work properly. And since the most common donor vehicles were engineered in the late ’60s, their geometry isn’t much more sophisticated than the earliest designs. More damning than that, their fixed track width doesn’t always fit properly in recipient cars.
The other method requires creating a frame jig that maintains the chassis alignment and cutting away the area between the firewall and framehorns. Only when the section with the spring pockets and control-arm mounts have been replaced with straight steel tubing will a frame accept an aftermarket crossmember and suspension. Though these aftermarket suspensions boast more sophisticated geometry and can be configured for different track widths, their installation involves labor that most enthusiasts either aren’t capable or willing to perform.
Fatman Fabrications has a third way. It carved a niche for itself by creating entire assemblies to update vehicles originally equipped with independent front suspensions to newer, more technologically advanced systems. These stubs, as Fatman refers to them, consist of a crossmember welded between a pair of rectangular tubes.
Like subframes these stubs replace a portion of a vehicle’s existing frame. However, unlike subframes the stubs match the recipient vehicle’s frame dimensions and duplicate the body mounts, bumper attachment points, and radiator supports. And because Fatman designs them for each vehicle it can tailor the track width to suit the specific application.
The breadth of vehicles that the company addresses boggles the mind: Fatman produces variations of these stubs to fit dozens of vehicles from the ’30s all the way to the ’60s. And while it covers the big players like Mopar, GM, and Ford products, it also covers the orphans—Kaiser, Nash, Packard, and Studebaker owners take note.
Though the individual stub designs vary per application they all have the suspension itself in common. Fatman derived the basic geometry from the proven, versatile, and highly supported Pinto/Mustang II platform. Though not exactly a cutting-edge design anymore, its geometry was quite a bit ahead of its time and far more sophisticated than the cars it went under. It has a relatively low roll center for good turn-in qualities, a camber curve that keeps the tire treads planted squarely on the ground in aggressive corners, and an antidive geometry that counters weight transfer under braking. Add rack-and-pinion steering to the mix and it’s clear why the industry so widely embraced it.
The particular setup we’re showing features tubular control arms but the upper units, the springs, dampers, knuckles (spindles), and steering rack, are functionally interchangeable to the OEM pieces. In fact, some Fatman crossmembers can use Mustang II components with some modifications. As you’re probably familiar, just about every brake combination fits the stock height and dropped versions of the knuckles.
What follows is how Marshall Woolery at Thun Field Rod & Custom installed a Fatman stub on a customer’s late-’40s Pontiac. Though the installation instructions describe the variations among models they can’t address the pitfalls that threaten every install.