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TECH: Johnny’s Ride Rigidified

Stiffen-up with Detroit Speed subframe connectors


By Rotten Rodney



Hot Rods & Custom Stuff preferred customer, Johnny Gibson has a mighty fine collection of muscle cars. In fact, two of his rides are amongst the mix of projects here currently. One is in the paint department in the final assembly phases, and the other—Johnny’s 1970 Z-28, is in for mechanical and cosmetic upgrades. At the time o’ this typing, however, it’s in the care ‘n’ custody of HR&CS’s fabrication department for substantial stiffening of its underdeveloped understructure.


From the assembly line, like the generation before, the second-gen’ F-bodies lacked the structural integrity to withstand the torque of big horsepower and/or the twisting forces of competition like drag racing, autocross, etc. Today we’re fortunate to have a solidifying-solution—subframe connectors from Detroit Speed & Engineering.


As a Detroit Speed dealer, HR&CS can provide the product, as well as install complete kits in just under a jiffy or so. Even those who’re crafty enough to handle their own first-time subframe connector upgrade would do well to at least take a tip or two from a HR&CS fabricator who does these jobs routinely. That said; we’d recommend the use of a bookmarker here.  


Following instructions; the upgrade begins with a plumb bob, after the installation of new rubber body bushings, or better yet for maximum stiffness, Detroit Speed’s own billet aluminum body mounts. It’s crucial that the body and subframe be properly aligned before fab’-work begins.


On Johnny’s car, the alignment was completed prior to this photo-urinalist’s arrival. This happens a lot, but on the upside, I’ve learned new ways to fill the blanks. Anyway, the body-to-subframe alignment procedure is covered in the kit’s instructions. From here let’s move a little closer to the bottom side o’ the car and see what else is involved.    


Here’s what’s supplied from Detroit Speed: left ‘n’ right subframe connectors, inside ‘n’ outside brackets, end caps, templates, installation DVD, and detailed printed instructions.


HR&CS fabricator Jeremy has already seen the movie, read the instructions and installed a good number of these kits before, so this job will move along quickly. Before the sparks begin to fly, it seems worth mentioning that caution should be taken to protect the car’s glass. How many of us have learned this the hard way?


In this instance, previous damage to the car’s floor is clearly visible. These small dented areas are best hammered ‘n’ dollied before any cutting of the floor begins.


According to the instructions, measurements should begin at the rocker panel pinch welds. Providing the car has not been damaged; or worse yet; damaged and previously repaired in these areas, the recommended procedure is the way to go. This car is no virgin, so Jeremy double-checks using his own alternative measuring points.  


With the supplied templates now trimmed from the instructions, Jeremy has opted to transfer the shapes to poster board. The slightly thicker material will be easier to trace an outline around.  


For the revised template’s final trim, this pair of professional-grade ambidextrous template scissors is the hot-tip-tool for the job.


As long as the bottom side of the car’s floor is clean and dry, a dull Sharpie makes an adequate scribe.


Now in addition to the paper protection for the car’s glass and remaining interior trim, a “tent” has been fashioned from random 2-by-4 remnants and a welding blanket. Since the first cuts will be to the bottom side of the floor, this ounce o’ prevention makes for good fire insurance.


Once satisfied with the accuracy of his markings and prior-to-cutting preparations, Jeremy let’s ‘er rip with a cutoff-disc-equipped angle die grinder.


Certain slices are best made from the topside. For these cuts we must break camp and remove the tent. But from this view, at least we can see that stray sparks are controlled.


With a rewarding “clang,” the first-fallen section meets diamond plate and concrete. Granted, that’s not very technical, but we think the picture is nice.


Here Jeremy makes a little fine-tuning adjustment to one of his initial cuts. For this, a high-speed, pneumatic hacking saw from one of our local tool sources is absolutely invaluable.


As supplied, the subframe connectors are a tad or two long at each end. After the unwanted floor sections were trimmed free, the subframe connectors were measured and trimmed to match. The slot at the rear of this subframe connector required a slight bit o’ relief, but for a first fit, this ain’t bad at all.


The fit is a close one, and tight in one place. With a gentle tap o’ the mallet, it slides in firmly enough to stay.


Although the fit is satisfactory, it’s temporary at this time. The supplied brackets are not yet attached and there’s still some preparatory work to be done to the floor.


Rubberized undercoating can be stubborn, and wouldn’t ya know it; this car’s got it on both sides o’ the floor. This type of material goes gooey when abraded, but eventually, after a while or two, it gives up and goes away.


So here’s a topside view of our fit-check. From here the subframe connector will assume a position on the welding table for further fabrication. 


The supplied end caps are the “cock for Dolly” just as they are. These are thoughtfully stamped just slightly smaller than the rectangular-tube subframe connector’s outer edges. A pretty little TIG weld will fill the recess nicely.  


For the TIG-welding tasks at hand, the shop’s Miller Syncrowave 200 is Jeremy’s machine of choice.


Jeremy has decided to make a quick cleanup pass over his end cap welds, but only where brackets will go. This is only to clean the metal in preparation for the next pretty little TIG welds.  


With the end caps now finished, the subframe connector is supported in position as it will be. Now the inner and outer brackets can be located and tack welded to the subframe connector. For this, the shop’s Millermatic 135 MIG welder is the hot tip.


Back at the bench once again, the subframe connector is ready to have its brackets TIG welded for keeps.


So far it’s been a day chock-full-o’ miggin’ ‘n’ tiggin’—and what else should be said about that? Perhaps I’ll come back and finish this caption later.  


Okay, how ‘bout this one: with the TIG-welding of the brackets now finalized, the subframe connector is in position and about to become a permanent stiffening member.


Of course, fire-preventative measures have again been taken. Since we can’t see what’s goin’ on inside the car while MIG-welding down below it, Jeremy pitched his 2-by-4/welding blanket tent as we’ve seen before, just prior to welding.


As we’re nearing the homestretch, the topside joints are MIG-welded as well.


When these procedures have been completed on both sides, the beefed-up areas will be chemically-cleaned and primed. The rubberized undercoating will be texture-matched and spot-repaired as well.


So, how will you drive yours? Perhaps you should consider a Detroit Speed subframe connector upgrade, too. As always, Hot Rods & Custom Stuff has you covered, and we’re here to help.