The beauty of the 1979-1993 Fox Mustangs and their 1994-2004 Fox-4 cousins is that their lightweight chassis has been scienced out for the quarter-mile and it’s easy to fill their engine compartments with horsepower. That said, the Fox and Fox-4 platforms aren’t perfect. Its suspension needs enhancement and often the chassis needs bolstering.
BMR Suspension is already well established with full product lines for the S197 and S550 Mustangs. Now the company is rapidly expanding its offerings for Fox and SN-95/New Edge ’Stangs. Recently the crew at BMR rolled out several new products for the ’79-’04 Mustangs. However, the product that caught our eye was a new take on reinforcing the factory torque boxes.
In addition to its new Tubular Upper Torque Box Reinforcement Kit (PN TBR005; $139.95), BMR offers upper and lower control arms, differential bushings, springs and subframe connectors for 1979-2004 Mustangs.
Bolstering The Boxes
These brackets are at the core of the Torque Box Reinforcement System, which ties the factory upper control arm mounts into the frame rails. When combined with the included crossbrace they serve to spread the shock loads from those launches across a much larger portion of the chassis, reducing torque box fatigue.
The torque boxes are a known weak point, even on a relatively low-power car with a good tire. — Tommy Stone, BMR
Over time the mounting locations for the upper control arms — know as the torque boxes — can fatigue from the stress caused by absorbing the shock loads when drivers launch aggressively on a sticky tire. That fatigue can lead to cracking and eventually to the control arms ripping out their mounts.
“You are getting flex at the torque boxes,” Tommy Stone, New Product Development at BMR Suspension, explained. “The torque boxes are a known weak point, even on a relatively low-power car with a good tire.”
BMR’s Colt Mills begins the process by removing the upper control arms and snaking the Torque Box braces into position. Once in place on the frame rail and aligned via the control arm bolt, Colt uses the brace as a template to mark the frame rail.
Along with bolstering the torque boxes on Fox, SN-95, and New Edge Mustangs, BMR Suspension has also added some new chassis stiffening products to its line. Both its weld-on tubular subframe connectors (PN SFC024; $109.95) and its weld-in boxed subframe connectors (PN SFC010; $249.95) join the factory subframes to stiffen the chassis.
The tubular parts offer basic stiffening, while the boxed units extend the full length of the floor pan and tie in the rear seat mounts as well for maximum stiffening. The latter units were installed on the New Edge car we used in our shoot, while BMR also has a Fox coupe in-house, which was the test mule for the tubular subframe connectors.
If you’ve ever owned a Fox-chassis Mustang, you know that its flexible chassis is one of its greatest weaknesses. If you pick one up and it doesn’t already have subframe connectors, they should be your first mod and it’s nice to see a couple more options to get the job done.
Heretofore, the solution for bolstering the torque boxes was to weld in support plates on the interior and exterior of the floorpan. It’s an effective method and one that BMR supports with its ownTorque Box Reinforcement Plate Kit, which can be bolted in or welded in on big-power cars. However, installing one of these kits might be a bit labor-intensive for those who don’t want to pull the rear seat and bust out the welder.
“BMR Suspension believes this style of torque box reinforcement (tubular upper) is a very effective, easy to install way to add strength to the chassis of a vehicle that greatly needs it. We have supported the control arm mounts on many other vehicles with this style of brace, and it works extremely well,” Pete Epple, Marketing Tech, said.
“The installation is very straightforward and can be done by even novice backyard mechanics. The three-piece upper torque box reinforcement kit takes almost the entire torque load that the engine applies to the chassis and uses the frame rails to keep the control arms mounts in place. This means more consistent launches and more horsepower and torque applied to the tires.”
A New Take
This is a bolt-on option — aside from drilling a couple holes. — Tommy Stone, BMR
That’s why Tommy and the clever BMR crew developed the company’s new Tubular Upper Torque Box Reinforcement Kit (PN TBR005; $139.95), which can easily be installed from under the car.
“This is a bolt-on option — aside from drilling a couple holes — that can help fix that, versus pulling out the interior, welding in plates,” Tommy said. “It is something that somebody could do in the driveway that will give you similar results. Or, if you already have the plates, this would just be further reinforcement, ensuring that you don’t have problems with the torque boxes.”
After removing the brace, Colt drilled the frame rail and slid in the support sleeve, which will allow tightly fastening the brace without crushing the frame rail.
As we mentioned elsewhere in this story, BMR now offers lower control arms for 1979-2004 Mustangs. The decision to create these parts was not taken lightly.
“After spending a lot of time watching the market, we felt the Fox platform is ready for higher-quality components, and not just cheap knockoffs of one design. When we started designing new parts, it made the most sense to begin with rear upper and lower control arms,” Pete Epple said.“These are simple to design, easy to manufacture, and make a huge difference in reducing wheelhop and increasing traction.”
As a result, the company now has a wide variety of control arms for Fox and Fox-4 chassis Mustangs, both fixed and adjustable.
“We released a line of lower control arms that included a chrome-moly, double adjustable lower control arms for race-style applications (no spring mounting provisions),” Pete explained.
“We also released adjustable lower control arms with polyurethane bushings or rod ends. These arms feature a new chrome-moly, telescoping adjuster unlike anything that’s been used before. This is an extremely strong, yet very compact design that allows everything to function like stock with no compromises in mounting or spring placement.”
Not to be left out, the company also adds more control above the diff with its selection of upper control arms.
“Like the lowers, we also designed a new compact center adjuster. These arms are available with either polyurethane bushings or rod ends, depending on the application,” Pete added. “…These give you reduced deflection over the factory stamped steel arms, meaning more horsepower and torque is applied to the chassis.”
That’s right, you could install both systems if your car is making big power and being set up to launch on slicks at the drag strip. If your Mustang will only see occasional drag strip or hot street duty, the new bolt-in system should provide plenty of support.
“Knowing that these cars have always had torque box issues, we decided to try a different route as to stiffening them up and tying the outer mount to the chassis, then tying the two together using the center brace,” Tommy said.
To find out just how easy this new system is to install, we dropped into BMR Suspension headquarters in Seffner, Florida, to document the process on one of the first production systems.
“It’s a non-conventional idea — because we are making the same thing that others are making with the conventional torque box kits — but we are just doing something different and giving people options that aren’t currently on the market,” Tommy added.
As you’ll see, it’s a straightforward operation and we also got a look at several of the company’s new Fox/Fox-4 chassis and suspension bits.
And, stay tuned, as BMR is in development on a number of other Fox parts, including a tubular K-member and A-arms.
For more on the BMR Suspension gear, you can visit the company’s official site here.
With the hole drilled and the sleeve in place, Colt slid the brace back into place and loosely bolted it in place.
Next he installed the cross brace, which connects the inner side of the two control arm mounts, and bolted up the upper control arms, whose bolts connect the two torque box braces. “It disperses the load from the outer bolt to the frame rail and then the inners tie together,” Tommy Stone of BMR explained. “So it stiffens everything up that way.”
To add more control and durability to the rear suspension, BMR offers billet aluminum differential bushings featuring Teflon-lined spherical bearings. The first offering is a bolt-in version, but a more affordable press-in version is on the way.
With the diff bushings in place, Colt slides on the adjustable upper controls (BMR offers fixed-length versions as well) and bolts everything up.
The last step is to install the coil springs and final tighten the fasteners adhering to the factory torque specs.