We’re not even sure why the aftermarket still calls it Mustang II. Back in the ’70s, kit car hobbbyists started relieving these cars of their front suspension components. It was an easy and, more to the point, cheap way to put independent suspension, rack-and-pinion steering, and disc brakes on a kit or component car.
The Mustang II (MII) suspension geometry originally came from the ’70 Pinto. It was designed in the late ’60s specifically as a cheap-to-make setup for a four-cylinder car. This made the MII system relatively inexpensive for kit car builders to purchase and fairly simple to install in their cars. The real bonus was that it had a narrow track, making it perfect for kit cars, and it also had rack-and-pinion steering—possibly the first American car to come so equipped. The system was simple and compact, and offered pretty good geometry. Perhaps best of all, the crossmember could be purchased separately from the local Ford dealer while the remaining components were readily available at the local wrecking yard.
The booming popularity of Mustang II suspension led to the creation of its own niche within the automotive aftermarket. Several companies have built (and maintained) their reputations on the popularity of the MII, and Chris Alston’s Chassisworks can be counted among them. Alston has been in the suspension business for 26 years and is known for fabricating everything from four-link kits to complete chassis for drag racers and street machines. He also has extensive experience in developing and refining the MII-based suspension. By the early ’80s, Ford stopped offering the MII crossmember through its dealer network, which spawned the crossmember aftermarket. Eventually, outfits such as Chassisworks started manufacturing—and improving—the rest of the components as well.
At first, Chassisworks’ (and just about everyone else’s) improvements were limited to manufacturing new tubular control arms and developing other cosmetic changes to make the systems more visually appealing. Eventually, coilovers replaced the coil/shock combination, making the ride height and quality much more tunable. Around 1990, Alston decided to do away with the strut-rod on the lower control arm and incorporate another pivot point into his crossmember. The original strut-rod design (inset) was the one element of the MII that could make installation tricky. Not only did it require an unusual attachment point in the frame, but that attachment point had to be in the correct position or it could adversely affect the performance of the entire system.
By redesigning the lower control arm into an A-arm design and incorporating a new rear mounting point that rotated on the same axis as the forward pivot, Alston eliminated the inherent binding experienced with stock-type components and caused by the two off-axis pivots.
By the late ’90s, the advent of computer-aided design changed the rules of the suspension game. So, armed with a sophisticated measuring device and an engineering workstation computer, Chassisworks now had the power to identify and rectify the shortcomings of the MII suspension and bring suspension technology to the next level. Alston decided that his best bet would be to study what made the MII work, identify what needed improvement, and then correct the inherent weaknesses. First, the crew at Chassisworks had to determine the actual geometry of the MII. For this, Alston turned to his engineering manager, Scott Rieger. Alston and Rieger started by removing an original crossmember from its factory rails and stripping it bare. Then, placing it on a perfectly flat and level granite work surface, the boys measured the dimensions of the crossmember and its mounting points using a Faro six-axis portable 3D CMM measuring machine.
This device plugs into a laptop computer, which keeps track of the measurements and how they relate to each other in three-dimensional space, accurate to 0.001 inch. With the crossmember plotted, they moved on to the rest of the components, measuring the control arms, spindles, steering rack, and antisway bar. With everything digitized, Rieger set about constructing 3D models on the computer—he calculated the change in geometry of every component throughout its range of motion while keeping track of changes in critical factors such as camber, caster, toe, bumpsteer, anti-dive, and roll centers. This provided Rieger with a baseline of the MII system’s capabilities. He then used his engineering expertise to alter the design by moving pivot points and changing the dimensions of the components until he had calculated the optimum geometry while staying within the basic parameters of the MII crossmember.
They didn’t stop at merely redesigning the system, though; they also engineered it to work in 15 available widths, from 24 to 38 inches. That’s right, Chassisworks offers 15 crossmember widths, 15 rack widths, and 15 antisway bar widths to fit any application. The rest of the components remain constant—that’s where most of the design work lies.
The improvements that Rieger implemented in his redesign are significant in that they greatly improve the driveability of Chassisworks’ Street Machine suspension system. The accompanying sidebars will give a clearer picture of how each modification improved upon the original design.