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Welding Roll Bar to Roof


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Hi Folks, when I welded a 4 point roll bar into my 240z I tried to get the top and back of the roll hoop as close to the roof support as I could to give me the most room for seats and helmets. Unfortunately, on the passenger's side its a bit too close, and as the chassis flexes the roof support bangs into the roll hoop making a really annoying sound. I've been thinking of just welding the roof support straight to the roll hoop as a way of preventing this and stiffening the chassis, but I'm worried about this causing issues with flexing the joints in the roof (specifically the joint at the top of the A pillar) and cracking the 50 year old very fatigued steel. The paint on both B pillars has already cracked at the leaded joint and I'm thinking of using a syringe to inject some paint or POR15 to keep it protected. The car is almost only used for autocross at this point but it's still street driven to and from and I don't want to create any new issues.

 

Has anyone done this before, and if so, did you run into any issues?

 

It would be incredibly difficult to get a file in and clearance the roof support where it's rubbing the roof support, but I guess anything is possible.

 

Thanks!

Noah

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Definitely weld the bar to the chassis. A buddy of mine ripped the A pillar off of his car at an autox in the 90s. A fabricator friend fixed the A pillar and added a 4 point, then welded one single probably 3" x 6" plate from the bar to the roof right in the middle where the map light is. He said it made a huge difference, and all of the interior panels stopped squeaking when he went in and out of driveways, etc. 

People do this all the time now with shear panels that usually have dimple die holes on the A pillar of cages, but you can do it anywhere the cage and chassis get close. I have smaller panels on the roof, the door bars to the sills, the main hoop to the inner wall just inside the doors, and around the A pillar.

I don't have pics of the top, but here is one of the hoop to inside of the door. FWIW, after I did this I learned about shear panels, and they really should be longer for better strength. Also doesn't have to be 1/8" thick. Thin metal does fine for this. .0625" is fine, .040 or .050 probably sufficient. Do some googling on roll cage shear panels and I'm sure you'll find more detailed info.

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Thanks guys, I'll try a couple of shear tabs between the hoop and the roof support, probably one on each side. Just yesterday I fixed a big rust patch in the dogleg which had been hiding under some bondo (nice job whoever fixed that last 😕 ) and that seemed to stiffen the car up substantially, no more banging when entering the driveway!

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I welded 4x 1.75" wide 0.06" thick strips from the roll hoop to the body, two on the sides right below the window frame and two to the roof support .75" outboard of the dimple die holes. I cannot believe how much quieter the car is and how much better it handles bumps, hard accelerations, sharp turns, etc. Its really incredible, wish I'd done this a year ago.

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I thought about doing the full-length strip with dimple die holes, but decided the added weight along with the compromise on metal thickness didn’t make sense for me. I thought about the metal fatigue concern too, so I opted for 14-gauge with the ends bent into 90’s. The fatigue will cause cracking/tearing at the extreme ends, so I paid special attention to those when I welded. Heck, it might still rip. 
 

I have the cage tied in several places (besides the rule-enforced spots with the 1/8”thk plate) 

 

three spots per side to the door jam.

where the front hoop nears the lower windshield sill.

where the front hoop bears the front roof support (both axis on this one)

where the roof supports over the doors meet the horizontal roof support behind your head.

 

Sorry, most of these are from before I painted the interior.


 

 

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Edited by AydinZ71
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  • 2 weeks later...

@Ironhead, I’m glad you chimed in, because I did a similar thing with my bar.  Mine’s bolted in, and I wanted to retain the ability to remove it when necessary.  I fabricated some bolt-in brackets which utilized those mounting points on the roof support and two beefy 1.75” tube clamps.  Provides two additional mounting points for the bar and the extra chassis stiffening Jon and Clark recommended.  BTW, love your car...beautiful build!

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