Project J bar and tower brace for my Dart.

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bentdart47

bentdart47

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Hello,

After recently changing over my front suspension to coil overs I wanted to do two things. I wanted to stiffen/strengthen/overkill the front end while also filling in the area where I use to have shocks in my old torsion set up. While I'm not finished yet I wanted to share my progress in case anyone is thinking the same.

Initially Carl at GTS was nice enough to bend me some nice 1 1/2" main tubes and 1 1/8" down tubes. He left them nice and long so I could fit them and make all the plates I needed for my custom application. In the first pic I'm beginning to get everything set up for the next step. Basically a lot of taking a little material off at a time, checking fit, rinse repeat until I was happy.

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After I got my main bars exactly where I wanted them I went ahead and welded them up to my attachment plates but not to the car itself. I wanted the ability to take the bars in and out throughout the fabrication process. In this picture I am fitting the down tubes. These will bolt from the bottom of my old shock tower.

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Here's one side after I finished setting up the down tube. I had to custom make washers that fit on the end of the down tubes.

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In this picture I'm getting set up to start building my tower brace. This will connect the two sides and be removable for maintenance etc...

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Initial planning for the tower brace. This is where I will leave this for now. I plan on building this with dimpled sheet metal in between the 1" bars for some additional light weight strength.

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Nice work!

Good to see someone actually taking all the structural considerations of swapping to coilovers into account when it comes to reinforcing the chassis. Not that a torsion bar car can't benefit from the same modifications, the A-body chassis was a little lacking in the front chassis stiffness even for torsion bars.

Dillinger Chassis made the J-bars that I installed into my Duster, pretty similar in design. Because I retained the torsion bar front end I needed to do something a little different for the shock towers, I actually boxed them on the outside and then welded a tube and landing plate that goes between the top of the shock tower and the bottom of the J bar. I also landed the J-bars right on top of my tubular radiator support brace, tying the frame rails together across the front as well. I've considered making an extra shock tower brace to run across the engine bay, but running it around the engine, keeping the shocks accessible and making it removable add some complexity to the process.

You can actually see the J-bar, shock mount brace and the radiator support brace all in this picture. Plus the reasons why I did all of that chassis work, 275/35/18's and 1.12" torsion bars (well ok, you can't see the torsion bars).
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I did something similar in my coil over Dart, my approach was to do it with as little tubing as possible to keep the weight to a minimum.

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I admire both you guys tremendously. ....but I just do not see the value of attaching to the vent sheetmetal.....if it went on thru to a cage, I get it.
Besides, an area near the winshield is not where I would want any additional stress transfer. For your applications, would not a Montecarlo bar of some sorts make more sense?

Just trying to get educated.....and always willing to learn.
 
Nice 72bluNblu we think alike. 67autocross I hear ya I gained 15lbs or so but I'm hoping to gain a rock solid front end. Hemi, I have plans for a through cage in the future although the vent sheet metal in the corners of the A body is actually pretty tough, plus when tied into the old shock towers... I figure the more points of contact and triangulation I can get the better. I also plan on bracing from my coil over towers to the underside of my old shock tower thus into my j bars further tying everything together. I will post pictures as I continue this project. Here's what we look like now.

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HemiDenny said:
I admire both you guys tremendously. ....but I just do not see the value of attaching to the vent sheetmetal.....if it went on thru to a cage, I get it.
Besides, an area near the winshield is not where I would want any additional stress transfer. For your applications, would not a Montecarlo bar of some sorts make more sense?

Just trying to get educated.....and always willing to learn.
Click to expand...

It's not just the "vent sheetmetal" that you're attaching to. The landing plates are attached to the upper cowl, sure. But they're attached right above the firewall seam. And as you pointed out, the windshield is attached to the same upper cowl. As are the A-pillars, the door supports that tie into the rockers, basically the entire structure of the front half of car runs off the corners off the upper cowl. So, that's exactly what you want to tie into, it's the strongest part of the whole car with exception of the C-pillar landing structures. That's also why large landing plates are used, to spread the load over as much of the cowl as possible.

Is tying the J-bars into the upper cowl as strong as running a full cage? Of course not. And the J-bar tubing is overkill for it's attaching points, but it's the easiest way to accomplish it. You could add sheetmetal supports like the US Cartool inner fender braces, but that only triangulates the area from the shock mount to the firewall (although that's still a big improvement over stock and a great addition). The J bar captures the shock mount and the front of the frame rail, triangulating a larger area. It's far stronger than just attaching a "loop" to the frame to capture the top of the coilover, placing all of the force right back onto the frame rail which wasn't intended to carry vertical suspension loads outside of the shocks.

Plus it works. I've put close to 10k miles on my Duster with the J bars installed, and that "vent sheetmetal" is holding up just fine. And the car is A LOT stiffer than it was before. Of course I also added subframe connectors and torque boxes to strengthen the corners and tie everything together. It's not like driving a full cage car, but it certainly helps deal with all the additional forces that come from running wide, modern compound sport tires and much higher wheel rates (like 300 lb/in plus sway bars).
 
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I have a cage in that car...to me it's the way to go if you are really want to stiffen up these cars. Lots of people don't like them on a street car but if you take the time to fit them well it's no issue.
I also believe in that these front clip to cowl bars are affective and make a noticeable difference to the over all stiffness of the front end area....but I have no real proof...only Bro science.

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I was able to get some time in this morning. Here's most of the welding done with the webbing started. I plan to dimple this sheet metal.

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I think I'm going to fit it once last time then pull it back out and paint everything that won't see heat while welding.

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Final fitment went good. I was a little concerned about things shifting after welding. I will be moving on to paint soon.

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Looks great! Should be awesome when it comes back from paint. Another design to file away in case I decide to make some kind of cross-tower brace myself.

Put it right up there with this one that is in the Hotchkis built Duster. Although theirs does not lend itself to use with a carb. Their shock mount braces work better for retaining the factory style shocks though. Maybe some kind of combination of the two styles would work for my Duster.
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Detail picture of their shock tower brace
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How do you imagine they would get paint under that bar with it being so close to the inner fender? Looks really clean though. I'm using some SEM two stage for mine, I'll post a progress picture soon.
 
No clue. Wouldn't be easy, at least if you were looking for a show quality finish.

But since that car is intended to be a full functioning road race car, I don't think they're too worried about it.
 
Welded in, blocked out and primed. Sorry this turned into a bit of a body work job as well. This is a road car but I need to have it looking it's best as well. I will get a finished picture when it's done.

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