Rob Kinnan
August 1, 1999
Photos By: Michael Johnson

Step By Step

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We forced new-guy Mike “The Chin” Johnson to labor on Editor Kinnan’s ’87, starting off by displaying the Kenny Brown Double Cross subframe connectors for all to see.
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The connectors are different for each side, and it’s obvious which one goes where when you hold them in place on the car. You know you’ve got a connector on the wrong side when it doesn’t line up with both subframe stubs. The cross-brace of the connector slips over the seat belt bolts, and is held in place with two (per side) nylock nuts and washers.
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We loosely bolted it in place, making sure to center it as much as possible on the car’s frame ends. The holes in the cross brace are slotted slightly, and the perfect positioning required pushing each brace toward the middle of the car as much as possible.
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With the connector bolted in place, we marked the frames, then removed the connector and sanded down the whole area to prepare it for welding.
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We used a Standard Abrasives pad on an air grinder to speed it up, but you could use a wire brush and sandpaper. It’ll just take a lot longer.
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Once the areas were ground clean, we put the connector back in place, positioned it, then tightened the nuts and went in search of someone who could weld it for us.
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For a $20 bill, a muffler shop ran a few beads to secure the subs to the car. The last step is to squirt some spray paint on the areas that were welded, to prevent the dreaded creep of rust.
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We installed the standard Kenny Brown Double Cross connectors, but for even more stiffness, you can opt for the Extreme Subs, which adds a jacking rail and an “Extreme Matrix brace” to each side. The jacking rails are welded in place just behind the pinch seam of the sheetmetal, and are handy for lowered cars because they make it easier to get a jack under the car with a flat.

Subframe connectors are an important component in the battle for traction with a Mustang, but many people don’t understand how something that stiffens the chassis can possibly help the car launch, so here’s the deal. The stiffer the chassis is, the more effectively the rear suspension can do its job and put the power to the ground. That’s one of the big reasons why tube-chassied cars launch so hard and straight. All that tubing provides an incredibly rigid frame, so there is no chassis flex to upset the suspension. The suspension links can do their work without having to overcome the force of a twisting chassis doing the funky chicken with the geometry.

For really healthy street Mustangs with street radials, a stiff chassis doesn’t matter much for traction, because you’re not going to get the car to hook anyway. Any kind of power at all, transferred through hard street radials, on an unprepped surface (no rubber down like at a dragstrip), is going to result in lots of tire spin. But subframe connectors still serve a major purpose in a street application. They make the car feel more stable, more surefooted in the corners, and they reduce body flex that leads to creaks, rattles, and stress cracks in body panels.

Now that we’ve convinced you that your Mustang needs subframe connectors, the next question is probably “weld-in or bolt-in?” Bolt-in connectors do a good job of stiffening things up, but not as good a job as if you weld them in place. Anytime there’s a bolt holding something together, there’s a bit of movement between the parts, regardless of how tight you’ve got it. With a welded seam, there is no movement. That’s why nearly every connector manufacturer and chassis builder highly recommends welding the connectors in, even if they are a bolt-in design.

We installed a set of Kenny Brown Double Cross subframe connectors in our ’87 coupe in under an hour, and then drove the car to a muffler shop to have them welded in place. The subs cost $109, and the welder charged us $20 to run the beads. The end result is difficult to measure with actual numbers, and we’re hesitant to bring up that “seat-of-the-pants” cliché so common to some magazine stories, but they really did produce a noticeable difference in handling. Our coupe always exhibited a weird waggle in high-speed turns, kind of like the rear suspension was loose, but it’s no longer there. Now, it’s time to address the rest of the suspension. Hello, Kenny…?