floor pans & rear frame rails: the parts and the welding

dbgrigsby93 · 10-06-2009, 03:22 PM

I'm gonna be replacing the floor pans (not the complete but just the full driver and passenger sides so tranny hump won't get cut out) and both full length rear frame rails with rear torque boxes on my 1973 mustang mach 1. The first thing is that I'm looking for good quality heavy gauge metal from a reliable company (NPD, California Mustang, Mustangs Unlimited, etc). I also need to know about jack points and how not to jack the car up and how to jack it up in a manner that will keep the car from twisting while the work is being done. Keep in mind that the rear axle will be dropped out and probably the driveshaft... which brings me to my next question. what all should I take off to do the welding? I'm just gathering information for now.

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2+2GT · 10-06-2009, 03:37 PM

Do one side at a time, support the car at multiple points, and do the worst side first.

MetalEd · 10-06-2009, 05:16 PM

I'll be doing the exact same thing to my floor in a few weeks.. hopefully not the front frame rails, but I won't know for sure until I get the floor out.
I've seen a couple people use wooden jigs to support the floor pans and frame rails while welding. I plan to do the same thing using heavy threaded rods to give multiple micro-adjust lifting points for the floor. Fit it between the garage floor and the car floor and adjust each point to the exiting car floor before cutting it out. If I need to, I can give a nut a turn to raise or lower the new floor just fractions of a millimeter before spot welding it in place.
You could do the same thing for the frame and set it as a guide before removing the existing frame, that way you are sure the new parts go in exactly where the old one was.
I thought about twisting as I remove the old floors as well (more danger with the frame). You could tac-weld a couple scrap support bars across/beside the parts you will be removing, then cut them out. When the new parts go in, just cut and grind off the tacs. That should hold everything in the exact position when you remove the support pieces and the tension is released by the removal.
These are just couple things I have thought about while planning mine. It might be over-kill, but I would rather do that than try to fix a bent car<G>.
I've seen a couple pages on floor and frame replacement specific for the Mustang, you should be able to search them out. Wish there were some videos....

2+2GT · 10-09-2009, 05:37 PM

zmetalmilitia · 10-09-2009, 05:46 PM

Looks like a wooden floor. In your garage? Nice supports by the way.

2+2GT · 10-09-2009, 07:30 PM

It's the second floor, not the ground floor. Plywood over hewn oak planks over 12" square oak beams. It's not going anywhere. The support frame was leveled with a beam level and laser. It's not going anywhere, either. Not my garage, a shop in the area.

MetalEd · 10-16-2009, 03:57 PM

Quote:

Originally Posted by dbgrigsby93

I'm gonna be replacing the floor pans .... I'm just gathering information for now.

I found this article at Mustang Monthly Magazine. on how to replace floor pans with lots of photos. You may want to check it out.

How to Replace Mustang Floor Pans

This is a very good site on Hot Rod Rust repair. it also has a specific area of floor replacement that covers things that weren't discussed here (Zinc Chromate primer on the frame rail and other areas to prevent corrosion)

Rust Repair and floor pan replacement

There are lots of good step-by-step instructions out there. I should have a really good idea of all the ways to repair mine when I get to it!
Good luck!