Floor replacement on a 70 Convertible - part one

I was pretty ecstatic when the convertible finally arrived safe and sound at my place last summer. It's a beautifully straight car with a  solid interior and a good running 351W. On the surface it was a real prize, but it was what was lurking beneath the surface that I wanted to get into and check out.

As suspected, things weren't all hunky dory on the underside of the car and despite the previous owners adamant declaration that there had been "no rust issues whatsoever" I discovered some of the most horrific patchwork ever seen on the underside of the car. Although the usual suspects in a convertible are the rockers when it comes to rust, the rockers on this car were amazingly solid, at least from what I could see.. You see someone years in the past had taken it upon themselves to "reinforce" the rockers by welding strips or 1/16 inch steel plates all up and down the underside of the rockers and floorpans. As if that wasn't tragic enough, they decided to hew out the front and rear floorpans (which really show no signs of any actual rust) and replaced them with miscellaneous sheets of random pieces of steel..

(Gee is my frustration seeping through yet..)

Ok ok, whining aside, the car is really in remarkably great condition but it needs some new pans. After polling some of the good folks on the mercurycougar.net website I actually ended up getting some great direction from my local parts store. Bruce at The Mustang Shop here in Calgary took some time going over how a convertible is different than the coupes and giving advise on how to go about un-"fixing" the pans in my latest acquisition. Now bear in mind that free advice is worth what you pay for it so always do your home work but in this case I know Bruce has restored several Mustangs in his day and had the luxury of working on many of our classic convertible rides so I took him at his word and thus begins our adventure into the pan swap.

The first decision we had to make was do full pans or partials. The partial pans are really just the area your feet sit in for both the front seat and back seat where as the full pan covers from behind the gas pedal to right up under the read seat lip. In my case I was torn. On one hand I wanted to get rid of all of the crazy 80s era "mad welder" artwork on the underside of my ride but I was concerned with having to remove both the seat platforms from the interior side and the structural reinforcement boxes from the underside of the vehicle. Initially I made the wrong call and was going to try and just do partials but this car really deserves a proper overhaul so Bruce graciously accommodated my request to change my order to a full set of pans. (After he had already made the order for the partials, sorry about that Bruce and thanks again.) I got my new pans home and gave them a good once over.

Now Bruce had two sources for the floor pans. There were "Offshore" pans and the good old "made in the USA" ones. The China pans are actually very well done and Bruce said he has had some really good feedback from people who used them so that wasn't a problem but he said that there is a lip edge on the offshore pans that wont line up right with the convertible. On the coupes they would be fine but I would need to go with the US sheet metal. I'm sure I could have trimmed the edges or something but for the extra $20 a side I wasn't going to sweat it.

Upon careful examination of my new floors I started to plot out the best place for the cuts to give maximum support to the floor and hide the "blending" area between old and new sheet metal. Much to my dismay it quickly became apparent that the mad welder who had attempted to "repair" the car in the past was going to dog me at every step in my endeavor as I uncovered more patchwork "support" strips welded to the inside areas of the rocker panels as well. Great, that just added another 10 hours onto my cutting and grinding time. It's all for a good cause though so I got out my trusty angle grinder and started in on my task.

As I stated earlier there really was no rust anywhere on what was left of the original sheet metal for the floors. The only real rust present was due to my arch nemesis (The Mad Welder for those just joining) who didn't properly seal primer/paint his welds. Much to my chagrin he had really taken out a lot of the old pan, in a very unmeticulous way I might add, and I was going to need to really try and keep my cuts as tight as possible to his welds to retain as much original floor as possible. It appears I had just enough space around the majority of his welding to make the cut along the rounded edge of the bottom of the floor pans. This would disguise the blending well once I replaced the pans and if I overlapped the old floor by about an inch it would help with structural integrity as well.

Measure 6 times cut once:

I am not a professional body man, far from it. Truth be told I think when I began this floorpan job it was the first time in 20 years I have taken an angle grinder to metal with the intent to do serious harm. That being said, the job didn't really scare me as I just applied all of the usual logic. Check, check again, then walk away for a while, check your cut lines again, confirm the fuel line is no where in the vicinity of your grinder, check your safety gear (grinding shield/visor, fire extinguisher, leather shop gloves, hearing protection, etc) then check your cut lines 2 or 3 more times... then, and only then do you even think about firing up the cutter. I had purchased cutting pads for the grinder. Do some quick research if you are going to be cutting metal as the pad type really impacts how well you are able to cut through metal. Most cutting pads are very thin (1/8th inch or less) and you will want to make sure your grinder supports thin pads.

Before I began making a mess of the interior of my car I pulled out everything flammable. All of the seats got removed, the carpet, all underlay etc. Then I brought my neighbour over who is a professional metal worker. He advised that I put up some pieces of plywood or blankets around the rest of the panels and dash of the car as the sparks and metal chips flying off the grinder would be red hot and leave burn pitmarks everywhere. Good call. I carefully positioned a bunch of plywood pieces around my work area. I didn't have a non flammable welding blanket and I've seen these hot metal chunks start so many fires I didn't want to chance it with regular blankets. I followed the instructions from my angle grinder on how to properly use the tool. I cut in 2-3 minute increments and gave the cutting pad 10 second breaks about every 30 seconds or so to allow it to cool down.

Very quickly I made short work of the rear drivers side partial pan. I used my soap stone pencil to mark my cut lines and the disturbing patchwork floorpan replacement quickly gave way to the grinder. Now the extra support boxes on the underside of the convertible were going to prove a challenge. After doing a quick cleanup on the interior floorpan I could see the massive spot welds used to attach those additional support boxes and they looked mean. 3/4 inch around and there were several of them. I really was not interested in tackling that kind of structural support work on the car so after soliciting more advice from Bruce at The Mustang Shop I decided to VERY carefully only cut out the floorpan from above the support boxes and leave them intact and attached to their original sheet metal mounting locations. This would mean some very precise grind work on both the seat riser platforms on the interior and then the thin layer of original floorpan sheet metal between the risers and the support boxes on the underside of the car.

The first step to freeing up the seat platform would be to drill out the spot welds along the sides as they hadn't been "Affected" by the mad welder and his adventures with strip metal. Or I didn't think so at least until I realized my tormentor had actual welded a long 16 inch piece of 1/8th inch steel over TOP of the spot welds along the rocker  panel.. Yeah.. More precision grinding for me, woo hoo!! I got the job done finally though and then drilled out the outside spot welds. This just left the front and back seams of the seat platform to be dealt with but I know I can handle that.

That covers the first 2 days of my grinding/cutting adventures with the floor pans. I am hoping next weekend I will be able to get back at the risers and see if I can carefully separate the seat riser from the floor so I can re-use the risers as they really show no signs of any rust or other structural issue. My adventures to date have been extremely education, enlightening and at times frustrating. I've discovered a great resource in Bruce at The Mustang Shop and I think that with perseverance and time I will master these panels. Look for the next installment of my adventures in floorpans in another week or two and thanks for stopping by.

I hope you found some little nugget of help or interest in what I've written. Feel free to send me comments or suggestions through the contact information on this site.

Thanks all.