Convertible Body Flex

[PurpleBeeper]

I've got a 70 Roadrunner convertible 4spd car with old-school frame connectors (tie the front/rear rails together, not the US Car Tool ones). The car is twisting quite a bit and I can tell this because along the top of the rear quarter panels in the corners of the body where the trunk lid closes (corners near back window), the metal is split about 3"-4" on both corners.

I'm not concerned about originality. I'm wondering if I can weld some type of brace below the cracks under the trunk? If it were my Mustang, I'd add a rear strut tower brace that I can buy online, but I don't think I've got that option with the 'runner.

Has anyone else had this problem & knows the answer? I know a roll bar/cage would help, but I'm undecided about adding a bar/cage.... but would like to leave it without a bar if I can. Thanks for any tips you can provide!

 

[Cranky]

How are the present frame connectors installed? IE, go through the back seat floor boards etc? If not, you will see gains if they did. Cut out the old ones and weld in the US Car Tool connectors and it'll help a lot. The car should already have the double wall rocker panels and the kick out torque boxes from the factory. How much rust is in the car if any....?

 

[PurpleBeeper]

Thanks Cranky.... the current frame connectors do not go through the floor. I can't remember the brand, but they're for a hardtop & they're designed as bolt-in. I had to notch the rear torque boxes & re-weld to the frame connectors. There's very little rust on the car, but one of the rocker panels was replaced (why I added frame connectors). I didn't know that convertible rocker panels were double-walled! The US Car Tool frame connectors didn't exist in 1985

Are there any other options?

 

[oldbee]

I used regular 2"x2" tubing to hold front&rear together, has held up for 35+yrs. welded, not bolted.

 

[5wndwcpe]

If the cracks are where the dutchman panel connects to the quarter panel, it's gets dicey. IIRC, that area is double layered (hollow) and the seam is filled with lead to boot.

 

[dvw]

I weld that seam solid on my race cars.
Doug

 

[PurpleBeeper]

If the cracks are where the dutchman panel connects to the quarter panel, it's gets dicey. IIRC, that area is double layered (hollow) and the seam is filled with lead to boot.

I didn't know the name, but yes, it's at the corners of the Dutchman panel. So, was there a crack from the factory with lead to cover it? As dvw mentioned, is welding a good idea? I'd considered welding it regardless, but I'm worried it will just crack again next to the weld. What else can I do to prevent that flexing? (other options besides US Car Tool frame connectors). I'm afraid if I put some sticky tires on it and hit the button I might tweak the whole chassis.

 

[5wndwcpe]

I very surprised it would crack at all. Lead is pretty forgiving in that it "moves" with the car somewhat. At least to the degree that if your car was flexing that much, I'd expect it to be showing up elsewhere first.

Was the car ever repainted ? That seam was not filled on the coupes/hardtops but was filled on the convertibles, so perhaps a repair was done and the lead was replaced with Bondo ? I'd dig into that crack and see what comes up - lead or plastic.

You can weld it solid, but bear in mind you'll need to remove any remaining lead first. If it were me, I'd want to know why the car is flexing that much to begin with.

 

[PurpleBeeper]

Yes, the car has been repainted a few times and it did have bondo over the crack. I think the body is flexing because it has no roof, it's a 4-speed, has a Centerforce clutch and a lot of torque. The frame rails are super solid front-to-back. I was just wondering if there was something like a "rear strut tower brace" available for Mustangs and/or some other trick that drag racers use to prevent body flex.

 

[Dennis H]

Take em out. Weld USCartool in. For starters.

 

[oldbee]

Maybe some kind of "X-brace" in trunk? Bolt-on connectors can get loose.

 

[5wndwcpe]

Yes, the car has been repainted a few times and it did have bondo over the crack. I think the body is flexing because it has no roof, it's a 4-speed, has a Centerforce clutch and a lot of torque. The frame rails are super solid front-to-back. I was just wondering if there was something like a "rear strut tower brace" available for Mustangs and/or some other trick that drag racers use to prevent body flex.

Convertibles have double walled rocker panels to add rigidity, making up for the lack of roof.

 

[Glenwood]

I'm thinking I better order some for mine! yikes

 

[moper]

Are you talking about the seam where the rear filler (Dutchman) panel hits the quarter panel on each side? Convertibles do not have a leaded seam because that would be the roof skin and roof bracing to the quarter panels. But the Dutchman to quaterpanels are spot welded on the flanges, and then seam sealed from the top. It's very common to have splits in that sealer if a cheaper product was used years ago. That's indicating movement - but it's not weakness.
Tie the existing frame connectors to the floor with some welded in tabs and you should be fine.