Horse Sense: A torque arm/Panhard setup is also referred to as a three-link design, a compact version of what's found on the S197 Mustang. It deals exclusively and positively with axle torque reaction (or windup), while the Panhard bar deals just as decisively with lateral movement of the axle housing. The packaging is more complicated than the Fox's factory four-link setup, but the results are worth it.
If you've been following along with our ongoing Fox 500 project, you'll recall that the main thrust (pardon the pun) of this heady exercise is to endow an innocent Fox hatchback-in rare T-top form, no less-with a Shelby GT 500's combination of hulking, blown 5.4 cammer from Ford Racing Performance Parts and a six-speed tranny from Tremec. Of course, introducing such potency to a flimsy Fox without proper chassis preparation would result in a 500hp, flexible, unpredictable, and dangerous beer can of a car. Such a car would make for an unhappy Editor Turner-the guy who commissioned this whole deal and requisitions my pay. I would never endanger the guy who requisitions my checks, so a safe and rigid foundation has been the first order of business.
Engineering and construction of the Fox 500 is taking place at Jackson, Michigan's Paul's High Performance. So far, we've documented installation of Maximum Motorsports' rollcage and full coilover front suspension, the latter teamed with a K-member specifically configured to mount a modular motor to a Fox chassis. In addition, our West Coast tech editor, KJ Jones, followed the assembly of our trick Strange Engineering 8.8-inch rear-axle assembly. With said axle complete and shipped to PHP, it's now time to hang it in place by way of a tough and precise, torque arm-based rear suspension, once again crafted by the West Coast chassis gurus at Maximum Motorsports.
Why a torque-arm setup? A torque arm, together with its accompanying Panhard bar, eliminates the biggest compromise in Fox factory rear-suspension design-the splayed upper control arms. Incidentally, the torque arm also eliminates any need for quad shocks. This all translates into positive control of axle torque reaction and side-to-side movement for much improved traction and far more predictable rearend tracking. With more than 500 ponies on call, a well-behaved rearend is essential.
So are good brakes, something we'll ensure in our next chapter of the Fox 500 saga.
The foundation for the whole rearend installation is Maximum Motorsports' full-length subframe connectors. These have a taller, more bend-resistant square-tube height, and are longer for increased weld area than Maximum's previous design. They're also a requirement for the torque arm, as its front crossmember welds to these subframe connectors. Between the connectors and the previously installed 'cage, the ol' Fox now has some backbone.
With the subframe connectors clamped in position, PHP's Karl Roekle MIGs them permanently in place after grinding the amazingly rust-free Florida unibody in the areas intended for welding. Note that the car is sitting on a roll-on hoist: The weight must be on the tires during subframe fitment so the unibody isn't flexed by being unloaded.
Extra rigidity results from crossbars that bolt to the rear-most bucket seat bolts, which are, in turn, welded to the subframes. It's to this ultra-rigid position that the torque arm's crossmember will eventually be welded.
With the subframes stoutly bridged, the PHP crew quickly set about removing the tired factory axle and its attendant hardware. Once the housing was freed, the old springs, shocks, quad shocks, upper and lower control arms, and sway bar went on the recycling pile. Naturally, the after-cat exhaust hardware also went on the scrap heap.
Before levitating the new axle into place, Karl and Mike Sears assembled the Bilstein-damped Maximum Motorsports rear coilovers and hung them from their top mounts in the hatch area. They also bolted Maximum's tubular rear lower control arms to the unibody.
We've already told you about the tough 8.8-inch axle assembly put together by Strange Engineering for our project, but let's recap: Starting with an FRPP housing, Strange fitted Mikronite-finished 3.73 gears (from Crane Cams and Motive Gear), a gear-driven Eaton Detroit TrueTrac limited-slip differential, and Strange's own 31-spline S/S Street axle shafts. The shortened housing was also capped with chrome-moly 9-inch housing ends with their larger bearings, as well as offset brake caliper brackets from North Racecars. The unnecessary quad-shock brackets were eliminated.
...
>>next page