The battle has been waged for decades—full-frame or unibody? Unibody chassis are lightweight, which makes them a no-brainer for performance, but that lightweight design comes at a cost. Stability in a unibody is less than optimum, hence the need for things like subframe connectors and stiffening bars, where the 79-04 Mustang is no exception in this area. While they are well known for being easy 9-second candidates, to get there you need some suspension work. One key weak spot are the rear torque boxes, which is why we turned to Wild Rides for our Project 666 Fox body Mustang.

Launching on slicks or even drag radials puts an incredible amount of stress on the factory torque box, more than what it was designed for. Eventually, the cracks appear in the fatigued sheet metal and the mounting holes stretch out. Initial signs of torque box damage include separation of the metal panels, broken welds, and distorted sheet metal.

Wild Rides Adjustable S-Box PN# 16177

• Three hole adjustability for instant center
• Increases hook by reducing deflection
• Virtually indestructible design
• Requires cutting and welding

The Advantages of the Wild Rides S-Box

Both upper and lower torque boxes can (and should) be reinforced before bolting on a set of slicks. If your car has already been thrashed at the track, that is OK, the Wild Rides S-box components will repair the damage and prevent it from happening again. In addition to the bulletproof design, the Wild Rides S-box also gives you adjustability; with 3 control arm mounting holes, you can change the instant center of the rear suspension to match your engine/transmission combination.

When paired with the upper S-box kit, you get the same adjustment potential as a true 4-link, while utilizing the stock suspension components for stock classes. “When asked, ‘do I need both the Upper S-Box & Lower S-Box’, the answer will vary depending on how much power and what some ones intentions are with the car,” said Gene Giroud of Wild Rides. “Both boxes give you more structure and adjustability.”

One look under 666 and you will see that it has been beat on. The factory torque boxes have been welded up; each seam fully welded to the body. If you cruise the forums, you will find that one of the most common solutions to the stock torque box problem is to weld up all the seams. Some of the Fox-body “forum experts” suggest seam welding on any car that has not seen any damage; that the welding is good enough.

The basis for a consistent drag car is to have a good stiff chassis.

“The basis for a consistent drag car is to have a good stiff chassis, with that you need the mounting points of the suspension to be ridged as well. The factory sheet metal moves/flexes, our S-Box won’t. It also provides a way for you to move the instant center around like a real 4-link car,” explained Giroud. As you can see from the mangled sheet metal on 666, that isn’t exactly the case. Not only does the seam-welding lack the adjustability factor, but also not nearly as effective as the S-box upgrades. Which is why we decided to bite the bullet and get the lower S-box with a kit from Wild Rides.

Prepping for Disassembly

The factory torque boxes are made of fairly thin stamped steel held to the body with a series of spot welds. While suitable for a stock Mustang, this is less than ideal for drag racing. You can see the band-aid fix of welding all the seams. In the end, it just makes more work for you to replace it.

There are a few key areas that you need to address before you start any disassembly. If the stock boxes are in good shape, you should make some reference measurements to ensure the new S-boxes are in the correct locations. This is done by pulling a string across the bottom of the frame rails, even with forward edge of the two 1-inch holes to about 10-inches back from the rear edge of the control arm mount hole in the torque box. Secure the string in position. Next, measure the center of the control arm mounting hole to the string on both sides. This will give you your factory reference point. The same procedure will be used to verify the new S-box location once it is set in position.

Disassembly and Installation

Before cutting out the original box, the mounting hole was measured and notated on the frame for reference.

Next, we used a plasma torch to cut out all the twisted metal. If this had not been welded in, you could use a sawzall and an air-hammer. With the metal cut, the boxes will come right out. There is a fair amount of leftover welds and steel, this has to be ground away.

The Wild Rides S-box is considerably nicer than the stock pieces. The biggest advantage here is adjustable mounting points allowing changes to the instant center. The S-box is a fully-boxed torque box, unlike the stock setup which is just a stamped panel spot welded to the floor. “Our S-boxes are constructed from 1/8” steel base materials and 3/16” steel for the actual bolt holes. Our design of the box and its install procedure has proven itself to be a bullet proof combination,

We spent a fair amount of time cleaning up the torque box location. There is a plate that installs above the S-Box on the interior floor, where the stock seat belt mount is. This needs to be lined up with the seat belt bolt, bolted to the car and then welded in place. The S-box slipped into place and we used an adjustable stand to hold it in place. C-clamps work too. They should be bolted to the car using the seatbelt bolts. We measured the location, using the center mounting point and adjusted the boxes until they matched on both sides to the original measurement. With everything lined up, a few tack welds secured the box

Then we used the MIG to lay down some nice, clean welds. Even thick metal warps when heated, so don’t just weld one big bead, space your welds no more than ¼” at a time 2-3 inches apart until the entire section is welded. We also welded the boxes to the frame rails as well.

With everything finished, we hit the new parts with some fresh paint. This looks so much better than the twisted stock torque boxes.

Finally, we bolted in the control arms using the center bolt to start off. Once we get to the track, this can be changed if needed.

While installing Wild Ride’s S-boxes is not super complicated, it is not a bolt-in procedure. You have cut, grind and weld many of the components in precise locations in order for everything to be square and correct. That means that if your welding skills are not up to the task (would you bet your life and the lives of others around you on them), then get some help from someone who is an experienced welder. By taking your time, checking and re-checking the fit, the end result will provide a serious advantage of an otherwise stock chassis Mustang. Though the advantages of this cost-effective piece will pay off in the long haul, helping us reduce chassis flex and adding adjustability!