The vintage Mustang in most folks' driveway is not the most flex-free platform in the world. The Mustang has--since its inception--been a unitized platform. This might make for a lighter car, but it also makes for a vintage chassis that is quite flexible when it comes to the whoop-de-doos and potholes. In some cases--particularly the convertible--this has been readily apparent right up to the SN-95 chassis. It is often quite disconcerting to feel the body undulate across bumps, or watch in horror as the gap at the leading edge of the door changes as the car is jacked into the air.
Ford saw that this would be a problem in 1963 as the engineers designed the chassis for the convertible. So they placed torque boxes under the toe board where the hardtop and fastback received none. The factory also added additional bracing along the doorsill, as well as across and under the tunnel of the convertible. This helped some, but the car was still not as stable as the hardtop. All that being said, we sat musing over what-ifs. What if you took the torque boxes that the convertible used and put them under the toe boards of a hardtop? Would this help stiffen the hardtop body?
We posed this question to Merv Rego at Classic Restorations of Central Florida, and his answer was yes. So since Project '66 needed floorpans and toe boards on one side anyway, we decided to invest in the torque boxes from KS Reproductions. The installation is not a simple one, but the enthusiast who has tackled floorpans before should be able to handle this with some time, effort, and careful measuring, as well as prudent cuts.
 1 Danny Gaydos is going to...  1 Danny Gaydos is going to be our tour guide in this excursion, and he is seen here prepping the seat pan for removal. He uses a rotary scuff pad to remove paint and make the spot welds more obvious. This isn't necessary if you are planning on doing only the torque boxes, but this car just happens to need floorpans as well. |  2 After he has exposed the...  2 After he has exposed the welds, the pan is cut away using a drill bit. This is done since the old pan is being pitched over for a new one. If the original floorpan is being used, then a spot weld cutter is a better idea. Check out the ones available from Eastwood (800) 345-1178. |  3 Gaydos carefully pries...  3 Gaydos carefully pries up one of the few nonrusty parts on the hardtop. Make sure that all the welds are cut before you do this, as it will keep the hammering and bending to a minimum on the other end of the job. |
 4 Next Gaydos cuts out the...  4 Next Gaydos cuts out the floor using a Sawsall and metal-cutting blade. At this point, the body should be in a spot that is more or less permanent during this repair. Note the amount of rust that was under the seat pan. This would be a good place to use some POR-15 before the new pan is installed. |  5 Gaydos cuts the old pan...  5 Gaydos cuts the old pan low so that all the seatbelt holes and good metal is retained. It is a good idea to do only one side at a time to keep the structure as sound as possible. |  6 This job is much easier...  6 This job is much easier on a hardtop because there is no torque box to cut away. Simply remove the spot welds on the framerail and hack out the toe board. You can leave the board in, but the torque box flange is sandwiched between the pan and the framerail. |