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What Are Mustang Torque Boxes & How To Repair Them

Created by Jay Walling
Date Created: 4/24/2019
Last Updated: 5/17/2021

Mustang torque boxes are often known for cracking or becoming damaged with spirited driving. LMR walks you through what torque boxes are and how to repair them.

Viewing this install and using the information shared is subject to the terms set forth here - View the LMR Install Instructions Disclaimer.

Many of you may be asking what is a torque box and what does it do? The 79-04 Mustang platform’s chassis came equipped with a standard four link setup. This included two upper and two lower control arms that connect the rear end of the vehicle to the chassis. In stock trim, these serve their purpose and are structurally sound. It is only when us true Mustang enthusiasts want to plant some serious power to the ground; these weak points can become a pesky issue.

What Are Mustang Torque Boxes? | How To Repair Them - What Are Mustang Torque Boxes? | How To Repair Them

As previously mentioned, there are four of these torque boxes on the car. When launching, cornering, or even daily driving our Mustangs around, these can become weak and brittle over time. This can be caused by natural decay and rust from the elements. These can also rip out from the car from excessive power that the factory did not put into consideration. This is especially common in the drag racing community. The extreme force some of these cars can occur, will literally pull the sheet metal out from the torque box area and can cause very costly repairs and downtime for your ride. The shear torque and rotational force from some of the higher horsepower applications can cause some nasty structural issues.

What Are Mustang Torque Boxes? | How To Repair Them - What Are Mustang Torque Boxes? | How To Repair Them

Starting with a clean slate is always best, a quick inspection of these areas is simple and can be done by any average Joe in their driveway. Things to look for will be rust and any separation of the structural integrity of the torque box area. Also, even check for any previous repairs that may not be up to par. If any of these are present, then it is best to consult with a local body shop or professional to address these accordingly to make sure that you have a good starting point. Over the years there have been many ways to add the needed strength to the torque box of the Mustang. Addressing these is the key point overall. Whether you use a simple bolt on application or if you choose to weld these into place, fixing it right the first time is always a good way to go. Some aftermarket options can include standard inserts made from plate steel. Others will tie all these together with added bracing for the strongest available benefits overall.

What Are Mustang Torque Boxes? | How To Repair Them - What Are Mustang Torque Boxes? | How To Repair Them

LMR offers a few different options from industry leading manufactures like 50Resto and BMR so you can beef up your torque box with confidence. As always, make sure you subscribe to our YouTube channel to keep up to date with everything 79-present Mustang and Lightning.

About the Video

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

Check out our YouTube channel for even more tech tips, installation videos, how-tos, and more. The best place to go for anything Mustang related!

Published on 2015-10-13
This lower 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 or weld in installation, however we do recommend welding them into place to further maximize the strength of the reinforcements. All needed hardware is included with the support plates and brackets.

Mustang Fitment: 1979 (79), 1980 (80), 1981 (81), 1982 (82), 1983 (83), 1984 (84), 1985 (85), 1986 (86), 1987 (87), 1988 (88), 1989 (89), 1990 (90), 1991 (91), 1992 (92), 1993 (93), 1994 (94), 1995 (95), 1996 (96), 1997 (97), 1998 (98), 1999 (99), 2000 (00), 2001 (01), 2002 (02), 2003 (03), 2004 (04) All (Excludes 99-04 Cobra w/ IRS)
Hey! What’s going on everyone? Landan here with Late Model Restoration. Today I’m going to be taking a look and installing a set of lower torque box reinforcements fitting your 1979-2004 Mustang.

The lower torque box is located at the rear of the pinch welds and right in front of the lower control arm. Over time, most Fox Body’s or SN95’s have lived a fairly tough life. Numerous high RPM launches on sticky tires can take their toll on the factory torque boxes.

Taking a closer look at this ’92 coupe, we noticed the lower control arms were completely wrecked. From the looks of it, a previous owner had some fun at the local drag strip, and someone obviously didn’t know how to use a jack. Unfortunately, these reinforcements won’t do anything for the jack mishaps. That’s going to be something you’ll have to address with a local speed shop or someone that knows how to work metal really well.

This particular lower torque box reinforcement kit will be manufactured from eleven gauge steel, so 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, we 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 flip the side, if you plan on bolting these in, be sure and paint the brackets and support plates prior to assembly.

Before we begin, any of you that own a 94 or 95 Mustang will need to enlarge the opening slightly for the bracket to fit inside of the torque box. Also, you may need to relocate the anti-lock brake wires. Now, let’s get this ’92 coupe in the air and show you how to install a set of lower torque box reinforcements.

Before you begin, take this time to paint the brackets and support plates if you are bolting them in. However, if you plan on welding you can wait until you are finished to paint. Remove the lower seat belt to floor bolt with a T-45 Torx driver. You’ll need to roll the carpet back, so removing a few scuff plate screws will help. Push the rear seat bottom toward the back of the car and lift up to remove it. With the seat out of the car, remove the lowest screw securing the rear interior quarter panel.

Pull up slightly on the panel pocket and roll back the carpet. Position the jute padding out of the way. Pop the plastic pocket away from the rivet on the interior quarter panel. The driver side will have a plastic cover over the wiring harness. Remove the two Phillips head screws and then set the cover aside. Scrape away some of the sound deadening material with a putty knife. Do the same for the same for the other side. Now jack the rear of the car up as high and as safe as you can.

Remove the rear wheels. This torque box was previously jacked up on and caused severe damaged. We cut some of the mangled metal away and then used a few crescent wrenches to reshape the metal. This would be an area that you would want to possibly re-weld. Push the rubber body plug through the floor. Using a breaker bar with an 18mm socket and a half inch socket wrench with an 18mm socket, remove the nut securing from the lower control arm bolt. Position the plate up through the torque box. The angled edge on the torque box reinforcement bracket will sit toward the rear of the car on each side.

Re-tighten the bolt to 100 ft/lbs. Use a three eighths inch drill bit to drill through the floor.
Some of holes will be at an angle; it may help if you use a smaller bit as a pilot hole first, then drill from the inside of the car. Do the same for the other side. Back inside of the car, scrape away any remaining sound deadening material. Vacuum the area and clean the holes up with a uni-bit or a deburr tool. Align the support plate with the holes; these are not side specific. Slide the bolts through the bottom and loosely tighten the lock nuts. Tighten the hardware with 14mm sockets. Do the same for the other side.

Reinstall your wheels and lower the car. Re-position the jute padding, carpet and reassemble anything in the interior that was removed. Reinstall the rear seat bottom. Double check your work and you’re all done.

As far as installation goes guys, this one should take around two hours, but it is something you can do at home, in your own garage. Like mentioned early, you can bolt these in or weld them in. Ideally, I would bolt them in, and then have a buddy or a reputable shop permanently weld them into place.

If you guys want to continue watching awesome install videos like this one for your Fox Mustang, then I invite you to subscribe to our YouTube channel. While you’re at it, head back over to the site and pick up some lower torque box reinforcements for your 79-04 Mustang at!
Thumbnail image of the author of this article, Jay Walling.

About the Author

Jay has written content for Late Model Restoration for over 10 years, producing over 120 articles. Jay has an extensive 25-plus-year background in automotive and is a certified Ford Technician. Read more...