Fox-bodied Mustangs aren’t exactly battleship sturdy. The unibody construction sees to that. Without additional support, and with some steam under the hood, it won’t take long before the doors don’t open and close very well. Wheel alignments go wonky, and as you dig deeper, the torque boxes (where the rear suspension mounting points attach) soon start to deform, stretch and ultimately tear. There are a number of different ways to resolve the problem, and many require welding. But the whole premise behind the War Pony is to bolt the thing together.
Given the parts availability for the Fox body, we quickly found excellent solutions to our dilemma: S&W Race Cars offers a bolt-in round tube frame connector set for the platform and Wild Rides Race Cars builds some equally good reinforcement pieces called “Battle Boxes.”
In the design of their frame connector, S&W ties the lower trailing arm (rear 4-link lower) mounting point directly to the front K-member mounting points. In between, the S&W pieces also hook the front seat mounts directly to the frame connector. In practice, as you get on the throttle, forces from the rear suspension (and slick) are transmitted through the frame connector forward. The rear frame connector mounting points are such that the lower suspension torque box (where the lower trailing arms mount) are heavily fortified. All of the pieces bolt right in.
The Wild Rides upper control arm support kit essentially sandwiches the factory sheet metal mounting points with heavy steel plate. One pre-fabricated plate neatly fits inside the upper trailing arm (4-link) mount pocket. The other pre-fab plate is fit inside the car, behind the back seat. A pair of heavy ½-inch bolts along with a pair of 3/8-inch bolts is used to secure the plates. Don’t underestimate the amount of strength found in a common thread; the entire concept of sandwiching pieces together with bolts to add strength is used with frequency in the aircraft airframe business. It has a fancy name in that industry: It’s called a “doubler.”
How easy is it to bolt in the hardware? It’s not difficult at all. Follow along was we fix the flex:
Before the subframe connectors go in, the front K-member must be installed. Here’s a peek at the round tube Racecraft cross member we’re using. A more detailed look at the Racecraft setup is coming soon.
S&W Race Cars frame connectors are round tube affairs. They tie the rear lower trailing arm mounts directly to the K-member, with a stop in between at the seat mounts.
Once the frame connector is fit into place (just slide it up and position the rear within the trailing arm pocket), loosely install the supplied nuts on the front seat mounts. Later, once everything is tightened up, we’ll remove these nuts and install a flat washer and a locknut.
Here’s how the rear of the frame connector fits alongside the trailing arm pocket. S&W Race Cars provides a ½-inch Grade 8 bolt for the trailing arm. Install it as shown (trailing arms are not installed yet). The bolt locates the back of the frame connector. In the second photo, you can see a smaller 3/8-inch bolt. That bolt is installed in a hole that already exists in the Mustang rear subframe.
Bolt the front of the frame connector to the K-member. We used the original Ford fasteners for this job. The Racecraft K-member incorporates only one bolt (the outer). On the inner (engine side) bolt, we slid a thick washer between frame connector and the body mount to ensure everything was square (see inset photo).
Moving backward again, you can now drill a pair of 3/8-inch holes into the lower trailing arm pocket, using the frame connector as a template. Install and tighten the bolts.
Now the seat bolt lock nuts can be fit with washers and tightened. Next, tighten the balance of the hardware.
This is the complete upper control arm (trailing arm) support kit from Wild Rides Race Cars. It includes all hardware as shown. The second photo shows the trailing arm pocket where the kit installs.
In order to install the kit, first remove the back seat and peel back the carpet and underlay.
Drill through two holes that already exist (partially) in the Mustang trailing arm pocket. Use the bottom support doubler as a template. Drill the upper hole first (the one shown with the bolt in it), with a ½-inch drill bit. You’ll have to drill as straight upward as possible (from the bottom up).
From the inside of the car, position the curved doubler plate as shown over the hole you just drilled. Add the spacer Wild Rides provides and insert the bolt as shown. We trimmed away the OEM rubber compound insulator so that the plate fit tightly against the floor.
All of the fasteners are in place, so the second ½-inch hole must be drilled next. Drill down from the interior side of the car. The reason is most drills that accept a ½-inch bit won’t clear from the bottom of the car. The pair of 3/8-inch holes is drilled from the bottom side first. More in the next photo:
Here’s a look at the double from the bottom side. Basically, you tighten the bolts to sandwich the factory sheet metal, which in turn reinforces the works considerably. You’re done.
Wild Rides Race Cars offers a support system for the lower trailing (control) arm mount points used in the Mustang body structure. These support pieces fit the outboard curbside of the lower trailing arm pocket. Ford built the Mustang with a small semi-rectangular shaped opening alongside the pocket. The Battle Box is wiggled into place through this opening and reinforces the sheet metal at that point. Four 3/8-inch holes are drilled upward from the Battle Box and attach to a supplied 6 x 6-inch steel plate inside the car. The bolts are tightened, which in turn sandwiches the lower trailing arm structure. By design, the trailing arm bolt passes gh the Battle Box. As you get on the throttle, the forces pass through the trailing arm into the Battle Box. Loads are then spread out over a larger portion of the body structure (instead of being localized in stock form).
If you elect to use a frame connector that doesn’t tie directly into the lower trailing arm support, then the Battle Box is pretty much a must-have. Combined with the upper support kit covered in the article, these pieces resolve the bent, torn rear suspension mounting points Fox-body Mustangs are plagued with. FYI, Wild Rides offers the lower battle box separately (P/N 161531) or with the upper and lower supports as a package (P/N 16213).
List of the components used in this article:
Quantity Part Number Description
S&W Race Cars
1 set 40-720 1979-93 Mustang subframe connector
Wild Rides Race Cars
1 set 161552 Upper control arm support kit
S&W Race Cars
Wild Rides Race Cars
Text and Photos by Wayne Scraba