by Richard Cordon III

Introduction
In continuation of my last article (Installing Subframe Connectors: 1965-1970 Mustang) that demonstrated how to lower quarter mile times by properly constructing the chassis to reduce flex and help correctly put the power to the ground, we at RatStang Restoration will be taking the next step in stiffening a 1966 Mustang Coupe by installing torque boxes.
Torque boxes are one of the most important basic structural add-ons for these early unibodies to help reduce side-to-side flex. This side-to-side flex is where most energy is lost through the vehicle's unibody.

In this article I will be providing information on the differences between two of the most commonly available aftermarket torque boxes for 1964-1968 Mustangs. I will also show how to install and reinforceme these torque boxes. This article will not be showing the process of a standard torque box install, but will be showing you how to reinforce a standard torque box by modifying it to the unibodies floor pans, floor supports, front frame rails, and rockers. This processs aids in providing the maximum side- to-side flex reinforcement capable from a standard torque box.

M117 and A117 Torque Box
There are a couple different manufactured torque boxes out there for the 1964-1968 Mustangs. The M117 and the A117 are two of the most common. The M117 is the more reinforced torque box of the two.
The M117 is manufactured with 14 Gauge mild steel and is further embossed for better rigidity. The M117 is spot welded to maintain a higher sheer strength over a factory torque box. The A117 torque box is more similar to those installed on Mustang convertibles through the mid to late '60s. A117 Torque Boxes are manufactured with 16 Gauge mild steel and are stamped and spot welded to resemble those of factory specifications.

M117		A117
Notice the embossing on the driver's side Torque box and the higher amount of spot welds.		The A117 is more similar to that of a factory torque box, with no added embossing and only contains the factory amount of spot welds.
Further embossing and stiffening on the leading edge of the M117.		Again , the A117 resembles that of a factory Torque box.
Reverse view of the M117		Reverse view of the A117

Conclusions on the M117 and A117
The M117 is a heavier and more reinforced torque box.

From my experience the A117 appears more precise and requires less modification during a standard torque box install.

Although the M117 torque box installed will provide more reinforcement, the A117 torque box would probably be the choice for a standard torque box install due to better fitment.

Getting Started
I will be modifying and installing a M117 14 Gauge torque box due to the added reinforcement it will provide. I will separate and modify the torque box for better fit, so fitment of the torque box as manufactured is not important. The M117 Torque box can be installed on any 1964-1970 Coupe or fastback Mustang and even 1971-1973 Mustangs with slight modification.

The modified and reinforced torque box install is a more precise and therefore a more challenging process. The project requires an experienced welder. However, with the information provided, a little knowledge, and the proper tools, this job can be completed in any shop.

Let's do it.

First, we’ll start by drilling out the spot welds from the top of the upper torque box (floorboard side as pictured).		Then we’ll drill out the spot welds from the bottom side of the lower torque box.
Use a flat blade pry bar and a rubber mallet to get between the two. Don’t be too aggressive when prying, you don’t want to have to fix bent parts.		With a little prying, the upper and lower half of the torque box should separate from one another. If not, find and re-drill the spot welds that are retaining the two pieces together.
Driver's side separated.		Passenger side separated.
Here is a typical fit of these particular torque boxes. They usually need some light modification to get them to fit correctly.		We’ll start by using a 2 lb. wide faced ball peen hammer to decrease the overall width of the part as pictured in step 9.
We will do this by working back and forth across the outside lip with the hammer to change the bend point of the lip to a more aggressive bend. We will stop once the bend point is about 1/16th of an inch from the width of the flap. As pictured above (Click to enlarge)		Test fit once again.