How to fasten the rear firewall?

A free file cabinet with "lots of life left" has given its lfe to be the firewall between me and the fuel cell in the rear of my Challenge Corolla. Attaching the sheet to the roll cage could be done by drilling holes in the sheet and spot welding it to the cage. However, this often results in me making bigger than necessary holes and welds after I manage to burn through the sheet too much. Suggestions on welding technique to do it right are welcome.

Also, I was in the adhesive aisle at Lowe's for other reasons this morning and saw tubes of Gorilla construction adhesive, which got my aging brain thinking........How well would construction adhesive hold the rear sheet metal in place? Think a 2 foot tall sheet across the main hoop of the cage and a fairly large "parcel shelf" from it to the base of the rear window.

I would give the construction adhesive a try.

But other ideas would be to braze it to the cage. Or weld brackets (small angle iron?) to the cage and then screw/bolt/rivet the firewall to that. Or cut slots/holes in the edge and use hose clamps thru the slots and around the bars. Or some combination of things.

All depends on what you have on hand and what is cheap and effective. Watching with interest!

Re construction adhesive - is it flammable?

Will you ever need to access the cell via the firewall? 

They make non flammable/flame retardant adhesive/sealant for exactly this purpose.

Is there enough material in the filing cabinet that you could overlap the tubes a bit and then bend the excess metal around the tubes somewhat? Once bent enough to "hug" or "sleeve" the tubes you could weld along the edges of the panel, parallel to the tubes?

Alternatively, what about a few tabs welded to the tubes, and then sheet metal bolted/screwed through the tabs? That would keep it removable and require pretty minimal welding.

Weld tabs to the cage + seam sealer gap? How professional are we looking to be here?

This is a perfect application for rivets. 

STM317 said:

Alternatively, what about a few tabs welded to the tubes, and then sheet metal bolted/screwed through the tabs? That would keep it removable and require pretty minimal welding.

+1, this is what I was just going to suggest.

iansane said:

Weld tabs to the cage + seam sealer gap? How professional are we looking to be here?

It's a Challenge car, so it can be pretty scabby, but I am trying to test my skills and do as nice a job as possible. I wouldn't mind folks looking at it going "OOhh" and "Ahhh!"

Is your Corolla a hatchback?

L5wolvesf said:

Will you ever need to access the cell via the firewall? 

Until just now I had never even considered if I can remove the plastic cell through the trunk opening. It's encased in a steel box that's welded to the chassis and the cell is easily removable when the body isn't on the chassis.......I guess I better check that.....

Tom1200 said:

Is your Corolla a hatchback?

No....it has a conventional trunk opening.

APEowner said:

This is a perfect application for rivets. 

Never even thought of rivets. That would be straight forward to do and would allow removal of the sheet metal should I ever need to.

For reference......

In reply to DeadSkunk (Warren) :

On my 1200 we fitted the firewall so it attaches just past the lower edge of the rear window and between the fender wells. Note Datsun 1200's have a folding rear seat with no parcel shelf, so the trunk not separated from the passenger compartment.  My car has a 5 gallon ATF cell; whenever I need to remove it I pull it out through the trunk.....not a big deal.

In reply to DeadSkunk (Warren) :

Remember no drilling of the cage tubing.

In reply to DeadSkunk (Warren) :

Now I understand.

I'd either make the firewall part of the body work 

Or 

Weld/bond/glue/rivet some Dzus fastener tabs on the square rails aft of the rear axle so that you could simply attach the need panels. You can also build a flap in the cover for refueling.

In reply to Stampie :

Good point. Rivets or bolts would have to go through tabs or flanges welded to the cage,

DeadSkunk (Warren) said:

L5wolvesf said:

Will you ever need to access the cell via the firewall? 

Until just now I had never even considered if I can remove the plastic cell through the trunk opening. It's encased in a steel box that's welded to the chassis and the cell is easily removable when the body isn't on the chassis.......I guess I better check that.....

I said that once. Now the firewall is attached with Dzus fasteners. I also bead rolled it to prevent the sheet from wobbling and being noisy. 

In reply to L5wolvesf :

I ordered a bead roller last night for that very reason. I still don't know that the wall needs to be removable though. With the body on the fuel cell may not come out the trunk opening, but trying to get it out through the cage doesn't look terribly easy either. I may have to re-do the fuel cell support structure and make it all bolt in from beneath the car.

DeadSkunk (Warren) said:

iansane said:

Weld tabs to the cage + seam sealer gap? How professional are we looking to be here?

It's a Challenge car, so it can be pretty scabby, but I am trying to test my skills and do as nice a job as possible. I wouldn't mind folks looking at it going "OOhh" and "Ahhh!"

No harm in that! I tend to operate the same way. I'd weld tabs on the cage, use weldnuts/rivnuts in the tabs and bolt the firewalls in place. Maybe door edge molding to keep rattles down/seal the edge. But that's me.

Stampie said:

In reply to DeadSkunk (Warren) :

Remember no drilling of the cage tubing.

I haven't built a NHRA cage in a while so my latest rule book is from 2014 and I'm not seeing that restriction.  SFI cages need reinforcements  (basically a welded on washer) around any wholes in the chassis including the cage but other wise I'm not aware of any rule prohibiting holes in a roll cage.  In fact some sanctioning bodies require at least one for measuring the tubing thickness.

I'm not advocating making swiss cheese out of the cage but some 1/8" diameter holes 6-8" apart isn't going to hurt anything.  Tabs are certainly prettier, particularly if the panel is removable.

Velcro... the miracle fabric of the 80's.    

In reply to APEowner :

I haven't seen a ruleset yet (granted, my head has been deep in SCCA-land) where they did not specifically say that things may not be attached to the roll cage via drilling the tubes.

Working around the negatives: Every rule set I have looked at lately specifically said you cannot drill cage tubes, period.

Tabs for sure, then go for Dzus fasteners so you don't lose screws in the parking lot.