[sled_fiend]

My project car has spent 30 years in a barn and has huge amounts of under carriage rust due to its use as a DD in Michigan before it was put away. I have some experience welding and fabricating so I'm not affraid to work on the car and do the necessary metal work but I am wondering if there is a way that I should brace the unibody while I am cutting out the floor pans and other rust areas.

With the carpet out I can see that the rust holes in the floor pans extend all the way up to the dimmer switch and under the pedals. I will be taking the dash out so that I can get at the cowl firewall to assess further. What would be the proper procedure for this type of repair?

 

[Sick467]

I cut out both toe boards, both front floor pans, rear passenger side floor pan, and torque box which required that the seat pans be removed. What I did NOT cut out was any part of the tunnel or any of the rockers, not did I remove any of the sub frame. The rear sections of the front subframe was exposed after I cut out the front floor pans, but they where still attached to the car. IIRC I did one side at a time and the car was supported as shown in the picture. The shell is not fastened in any way to my dolly, merely supported in front of the rear wells and behind the front well at the subframe only.

I had no flex problems whatsoever, BUT my car was completely shelled out. I also had the car up on steel horses for alot of the under-carriage work shown in the third pic. Where the second pic shows it going up for the horses.

 

[Yadkin]

Nice job. Rust repair is probably the hardest type of work. :bigthumbsup

 

[sled_fiend]

Thanks for the pointers. I like the idea of using tall horses to work under the car. Did you weld those up yourself from square tube? Right now my car is on jack stands so can only get it about a foot to 18" off the ground, just enough to get under it comfortably with a creeper.

Nice pole barn. Looks like a nice shop to work in.

Do you have any more pictures of your rust repair? I'm not completely familar with the sheet metal anatomy of the mustang, I know what the frame rails are and tunnel but what is the torque box?

 

[Sick467]

The Steel horses are welded/bolted 3" square tubing (14 or 16 ga). The old shell is actually very light and can be easily moved and lifted up one end at a time with by two people. Two to lift it up, then one person can hold it while the other moves the horse into place.

I actually did alot of the work like you said - on a creeper or flat on the ground with the car on the dolly. I spent alot of time grinding,welding, grinding, welding, then grinding and it was much easier to lay flat on the ground and do it than to sit or stand with my neck craned back.

I will try to gather some more pics of my repairs tonight. Don't hesitate to PM me if I don't get some up by next week.

And front torque boxes are a somewhat triangluar metal box that is weld below and in front of the toe board (directly behind the front wheel wells). It ties the toeboard, firewal, & frame rail together. I beleive the story goes...Thru to 66 did not have them, 67 & 68's had at least one, maybe two if it was a V8 model and definately if it was a vert. Something like that anyhow:?:. My car had one on the drivers side, it now has them on both sides. There are also rear torque boxes under the rear seat area that tie the floorboard, floorpan, & frames rail together. I think all cars have two, one on each side. The guy in the pic is putting on in.

Anyhow, start with the link below and do yourself a favor and Google "Mustang Floor Replacement" and you'll have plenty of stuff to read...

How To Replace Floorpans

 

[Sick467]

Here's a few (too many?) pics. PM me with an E-Mail address if you want more. The pic show the process for one side. The rear pan that is show is a piece that a PO had made and rivited in. It was made pretty well so I re-used it and welded it in.

Enjoy,

 

[Yadkin]

That must have been a bear to keep it all lined up when you cut out all the floor like that. I would have ended up with diamonds instead of rectangles.

 

[sled_fiend]

Thanks for putting the pics up. Just seeing the process clarifies a lot for me. I can see I need to build up a collection of vice grip clamps and eagle beaks!

I noticed that you lap welded your pans in and I've seen others but weld them using special clamps that set a specified gap for welding the sheet metal. Is one method better than the other or is the but weld method just to achieve a factory appearance?

 

[Lizer]

the idea is butt weld is better because it does not have an overlap that can collect moisture and potentially rust out. That and it doesn't change panel alignment. So butt weld is most desirable, and I find them not too difficult to do. You do tend to get a little more warpage at the site of the weld.

With that being said, ALL factory welded seams on your car are lap welds...so they can't be that horrible if the factory did them as well. You just need to seal them well with a quality 2K seam sealer (ie Pliogrip).

 

[Sick467]

This was my first floor pan replacement, but not my first sheet metal work. I have always lapped my work where possible and even done some crimping for exterior panels. BUT, properly done butt welds can be as easy and yield better results ( I think). I just have not got the nerve yet. I have enough experience now and have done some butt welding where lap welds where not possible and have found them to work out well. My early fears were not getting the seam cut right and burning holes at the butt joint. A lap joint is more forgiving wrt to both fears.

Lap Pros:

1. Forgiving wrt fit.
2. Forgiving wrt to blow thru (too much welder heat).
3. Yields a stronger piece (you end up with two weld seams if you do both sides).
4. More easily acheived by the novice without as much warpage.

Lap Cons:

1. Double the welds.
2. Double the grinding.
3. Non-Stock results.
4. Panel offset (when done without crimping).

Now that I have some confidence in welding, I beleive the butt weld is the way to go. However, my car is all welded up and I'll have to wait until my next project to try it out.

 

[Yadkin]

What kind of welder did you use? Wire feed?

 

[sled_fiend]

I've been looking at the Eastwood 120v/135amp MIG welder. It has continuously variable amperage and wire speed and sells for $339, a comparable Lincoln 140c like my buddy has goes for about $750 so it seems like a pretty good buy.

Do you guys know if the continuously variable settings make welding sheet metal much easier or could I broaden my search to include units with tapped adjustments. Since tapped units are much more common I can find those used pretty regularly on craigslist.


Also, what is the silver paint that you used to coat the repair? I was considering using a product called chassis saver. its supposed to be good for putting over tight surface rusted metal as well as clean metal and is supposedly really tough and even flexible. From what I've read you can brush it on and it will smooth out to a good finish or you can spray it.

 

[Yadkin]

I haven't done body work in 20 years and at that time all I had (still own) my old Craftsman stick welder. I bought it originally to do frame repair. Huge PITA to weld sheet steel.

For paint I used to use Rustoleum red primer. That always seemed to work well in areas that wouldn't get the finished color coat, like the underneath and interior.

 

[Sick467]

I used a Century (Cheapo) wire feed fluxcore welder (no gas). It has continuous wire feed speed, but only 4 incremental heat settings. It does a fine job. Gasless or fluxcore does not produce the prettiest of weld so it takes a little more grinding and rewelding to clean it up, but certainly better than maintaining/buying gas.

And the mutliple colors you can see at different stages of my projects are various type of leftovers from other projects. The silver was an aluminum oil based paint for outdoor use. It was my Grandfathers and he's been passed for 30 years. I figured if it was still good then it would certainly last on the floor board. Probably has uranium in it.:gringreen I also used alot of enamel left-overs. My motto is "layers and layers of paint". Let each coat thouroughly dry before applying a different kind and rarely did I have any compatibility problems. If there is one thing I have learned by disassembling old cars - wherever the paint was thick (like runs and puddles), it was protected and did not rust. My undercarriage has at least 5 coats of paint and most where brushed on. No undercoating for me, thank you.

 

[Yadkin]

I do the same thing. A small repair I'll grab the oldest spray can I have and use it up. A bigger one I'll open up any oil based paint rated for metal, oldest first.

We agree on undercoating as well- its crap. It looks awful, smells worse and doesn't work as well as several layers of paint.

Thanks for the info on the welder. I'm thinking of getting back into the hobby and a cheap wire feed will be my first purchase.

 

[Lizer]

I've been looking at the Eastwood 120v/135amp MIG welder. It has continuously variable amperage and wire speed and sells for $339, a comparable Lincoln 140c like my buddy has goes for about $750 so it seems like a pretty good buy.

Do you guys know if the continuously variable settings make welding sheet metal much easier or could I broaden my search to include units with tapped adjustments. Since tapped units are much more common I can find those used pretty regularly on craigslist.
.

I have that Eastwood welder and I'll go on the record to say it really is a fantastic welder. It's put together nice and works really well. It's assembled in China but was designed in the US. If you compare it bit by bit, it's comparable on all levels with the 110V lincolns and millers in its same class, only they don't have infinitely adjustable voltage and wirefeed.

I haven't used a stepped setting welder so can't comment on it. I learned on a nice Miller with full adjustability. I personally like it so I can tweak my voltage or wire feed speed just a bit if I think I need to cool a weld down a bit, heat it up a bit if it's thicker metal, or make minor adjustments if I'm not getting a good bacon sizzle sound.

The initial cost for the tank is expensive, it will run another $100-200 for a smaller one, but that's a one time fee and after that you own the tank, then you can just get it exchanged. Filling it with gas is cheap, $20-30 a fill, and one fill lasted me hours of welding with my regulator set at around 13 psi. In my opinion it's far worth it to spring for the extra $200 or so up front and get a tank set up as opposed to buying a cheaper flux wirefeed welder. On the other hand, that Eastwood Mig can also run fluxcore wire so it can be used gas-less. Then you'll already have a nice welder set up and can buy your gas later when you decide to spring for it.

 

[sled_fiend]

I ended up finding a Snap-On FM140-A at a pawn shop, got it for $300. It has 12 stepped settings for the voltage and the wire speed in infinately adjustable. I've only used it with flux core wire so far welding 1/8" plate on a frame repair on my truck project but it seems to work really well. I'm pretty excited to get to work on the mustang with my new toy!