How To: Install Mustang Upper Torque Box Reinforcements (79-04)

Upper Torque Box Reinforcement Kit

This particular upper torque box reinforcement kit is manufactured from eleven gauge steel, so it will add plenty of beef to those aging, factory torque boxes. They will feature bolt-in installation for those that really aren’t going to launch the car hard anymore. However, I do recommend welding them into place to further maximize the strength of the reinforcements. If welding will be your go-to method on getting these torque boxes installed, make sure you grind the area clean before you weld and then apply some sort of rust-prohibitive coating. On the flip the side, if you plan on bolting these in, be sure and paint the brackets and support plates prior to assembly.

Required Tools

• Jack
• Jack Stands
• Drill
• 1/2" Drill Bit
• 3/8" Drill Bit
• Body Saw or Cut Off Wheel
• Socket Set
• 3/8" Socket Wrench
• Rust Prohibitive Paint
• Phillips Head Screwdriver
• Welder (Optional)
• Sanding Disc (Optional)
• Razor Blade
• Putty Knife
• Vacuum
• Wobble Socket
• Safety Glassses

Installation Instructions

1. Remove the rear seat backs and seat bottoms from the car.


2. Safely support the car via a lift or jack stands.


3. Remove the rear upper control arm hardware and then remove them from the car. (Because of the pinion angle, you may have to jack up on the front of the rear end so that you can easily remove the bolts.)


4. Slowly lower the rear end down as much as it will go, but be careful not to overextend the rear upper brake hose.


5. Verify that the long M12 bolts pass through the two upper holes in the torque box.


6. If they don’t, elongate or widen the holes to accommodate the bolt. Verify that the bolt passes through each hole cleanly and is straight up and down.


7. Hold the lower plate in position and verify that the holes are in line with the holes in the torque box.


8. Use a half-inch drill bit and drill through-holes into the underbody of the car. When doing this, MAKE SURE that the drill bit is as straight up and down as you can get it. You can also use a smaller, 3/8" bit, to serve as a pilot hole and then open it up from inside of the car with a stepped bit.


9. Do the same for the other torque box.


10. From inside of the car, prep the floor area for the upper reinforcement plate.


11. Position the plate over the holes that you just drilled and then trace the plate with a marker.


12. Remove the plate and then carefully heat the factory sound deadening material with a heat source. Whenever the material gets soft, use a razor blade and cut the marked areas.


13. Reheat as needed and then gently remove the material.


14. Deburr the drilled holes and do the same for the other side.


15. Temporarily install both sides so that you can mark the upper plates and drill the two 3/8" holes with them removed from the car.


16. Someone will have to be underneath the car and the other person inside of the car.


17. Position the lower plate into place and feed the two M12 bolts through the holes. From inside of the car, install a spacer, then a washer, and loosely tighten the nut.


18. Do the same for the other M12 bolt and then tighten the hardware enough to hold everything in place.


19. From underneath the car, use the two smaller holes in the lower plate as a template and drill completely through the floor with a 3/8ths bit. There are multiple layers of sheet metal, so it’ll take a little bit of effort to do this.


20. Once you’re through the floor, have your friend hold the upper plate to the body of the car with and use the drill bit to mark the backside of the plate.


21. Go ahead and repeat these steps for the other side and then disassemble everything.


22. Deburr the 3/8" holes.


23. Now you can drill the upper plates off of the car. Use a 3/8" drill bit or a stepped bit and then deburr both sides of the plates.


24. If you’re not welding the upper plate, go ahead and prep both plates and the spacers for paint. If you’re welding the upper plate, just paint the lower plates. The upper plates and spacers will be painted after you weld them.


25. Scuff these parts with a medium-duty scuff pad and thoroughly wipe them down with a wax and grease remover.


26. Be sure and paint these components in a well-lit and well-ventilated area using a coating or paint that offers good resistance to rust and corrosion. Thoroughly cover each part with paint. Allow adequate drying times between coats and rotate the parts as needed. Whenever you’re finished, allow the paint to fully cure before assembly.


27. After you paint the torque boxes, be sure and touch up any areas around the torque box where you exposed bare metal.


28. When the paint is fully dry, you can begin the final assembly of the torque boxes.


29. Position the small bracket into the torque box and feed either one of the bolts through the holes. The person inside the car will need to install the hardware.


30. The smaller hardware will have a washer followed by the nut; and the larger hardware will have a spacer, washer, and then a nut. Make sure the flat side of the spacer is facing up and the angled side is flush with the bracket.


31. It’s recommended that you apply some red thread locking compound to the larger bolts and then fully tighten all of the hardware.


32. Go ahead and do the same for the other side.


33. If you are going to be stitch welding the upper plate to the floor; you’ll want to remove some additional sound deadening material so that you can properly prep the area for welding.


34. Once welded, mask the surrounding area and paint the plate with a rust prohibitive paint.


35. Reinstall the rear upper control arm and tighten the hardware.


36. Get the car on the ground, reassemble your interior, and then you’re good to go!

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Installation Diagram