The previous owner butchered the bolt threaded mount welded into the firewall. I have tried unsuccessfully to save it by rethreading it out to a larger size. Thinking of drilling through the firewall and placing a permanent nut on the backside of the firewall. Problem is the gas tank (this is s/n 744) wrapped in fiberglass sits flush against the firewall. Has anyone undone the metal strap that holds the gas tank and moved it backward to allow access to the backside of the firewall? If I can gain access, I will drill through and JB Weld a nut into the firewall allowing me the ability to finally secure the upper bolt. Dont want to attempt to cut the threaded tube out and replace. That seems difficult.
JB Weld will never hold something Like that. I think I'd weld a stud in the hole and use a nut on the outside, then work on a creative way to make it look good. That requires real welding though.
All the JB has to do is keep the nut in position and not spin . I was going to put a backing washer against the FW and then the nut. Tighten the bolt and then JB them to the firewall. But I like your suggesting of welding a stud in the hole.
That bolt is a stepped shoulder bolt to allow the upper seat belt mount to rotate. I've removed the tank strap and shuffled the tank back for access successfully in the past.
Seat belt bolts are pretty much universally 7/16-20 UNF, if it were me I'd drill out the existing hole get some tubing to slide in, weld up and tap a new thread.
The early cars don't have a top mount that rotates. The bolt totally locks the belt to the trim. My passenger side is the original metric bolt and the top of the harness is just the metal tab. Regardless, thanks for the confirmation you have moved the tank.
Would it be easier to thread the tube before installing? Or are you going to drill through both sides of the Firewall brace and weld both sides?
I guess you are if you are moving the gas tank.
I found that anchor point to be too low, so it did not properly thread through the harness hole in the top of my Recaro seats.
Using 3/16” steel plate, tubing and a nut, a new anchor point was fabricated. A clearance hole was then drilled in the top beam of the firewall and the plate welded in place.
If you have the ability or access to the welding skills for this approach, I believe it would serve your purposes quite satisfactorily and be much easier and more permanent then fighting with a gas tank and using JB Weld.
My passenger side is the original metric bolt and the top of the harness is just the metal tab.
I'm willing to bet it's not metric thread but 7/16-20 UNF, which is very close to M12 x 1.75 but far enough off it will damage the threads.
The forum here states the original bolt was an M11. I have one original bolt on the passenger side which confirms that.
7/16-20 is an exact fit to the 11mm. Both are scarce.
Isn't there enough metal to use a helicoil insert?
Careful working there. I've already cracked the glass from over tightening (or just tightening) the roll bar.
Apparently that bulkhead is a little flimsy?
The tube is very thin to begin with so I would be very concerned a helicoil would pull out of whatever is left once I tap it. thanks for all the input.
We've fixed a bunch of them. Don't trust you life on helicoil or epoxy. Simple fix: Push out your rear quarter window real quick, slide a piece of flat steel around where you think the hole is, drill it out all the way through. You will not touch the tip/edge of the fuel tank if you're careful, it's lower than you think. Safety first, slide a slab of steel for safety & drill away as afore mentioned. Apply any nut/bolt configuration your little heart desires. We use a thick 3" large seat belt washer on the fuel tank side. It'll NEVER come'a'loose. Replace the glass using a piece of rope. Quick job no big deal.
Thanks for this. You answered my original question. My side windows are already out and I can access the firewall, BUT the gas tank (early '71) is flush against the foam pad glued to the firewall. There is no way I can get a nut back there without moving the tank backward. Have you encountered this?