Floor pans, what to save, what to cut out

[drdano]

Maybe a question for the body guys here.  I've got some floor pans on my '62 Galaxie where some sections are rotted all the way through, obviously those areas must be replaced.  How do you gauge what other sections to do as well?  The toe boards have holes, but further back towards the seat area only the top of the pan is rusty.  On the bottom side in the same spot if I chip a chunk of the undercoating away, there is still primer under there and it's not rusted from underneath.  Under the seats and out of the foot wells the metal still has factory paint and no rust on both sides.  I assume this is kept.  That middle area, I'm having a problem gauging what stays and what goes.

1- Rusted through = replace
2- Not rusted through, and no rust on the other side =
3- No rust, still has factory paint both sides = keep it

Thanks guys

[jayb]

I use the ice pick method    If I can take an ice pick or a scratch awl, or something else sharp, and pound it into the floor with my hand, and it doesn't go through, I keep it.  If it does go through, it gets replaced.  Always amazes me  how a floor can look OK in some spots, but not pass that test...

[drdano]

Sounds reasonable enough.  What do I do with the sections that pass this test, but have the surface rust/pits?  Rust converter chemical and then prime/paint/whatever?

[Heo]

I you repair a rusted area  cut away a little extra atleast to an unpitted area. often faster than
get rid of the rust to get a good weld. Wirewheel on an angle grinder and a small one on a cordless
drill works okay to get rid of surface rust if its not possible to sandblast

[cjshaker]

Sounds reasonable enough.  What do I do with the sections that pass this test, but have the surface rust/pits?  Rust converter chemical and then prime/paint/whatever?

Lots of variables here. If it's just pitted, and not through the floor, I'd scrape it, wire brush it and coat it with POR-15, or at the very least, primer it with an epoxy primer like DP40 and then topcoat it (if you can even still get DP40, I think there's newer "safer" stuff out there now). It'll never rust again. POR-15 is an excellent product for stopping rust, and as long as it's not in a highly visible area where surface finish is critical, you'll never know it's there.

If you just have a few pinholes, but the rest of the metal seems sound, I'd still do like above. The POR-15 will take care of small pinholes and stop the rust from getting worse. Of course there's a point where, if the pinholes are too big, too close and the strength of the metal has been compromised, you have to move on to the next option: either patch or replace.

I do the pick thing also, although I'm not sure I'd do the "pound" thing. A sharp awl/pick can go through steel pretty easy if the metal has thinned at all, even if it's just done by hand. I just push on it hard. I don't believe in replacing factory floor metal unless it's necessary. Unless you coat the seams and rustproof it where it's been welded, it WILL come back. As long as the seams are good, and the majority of the steel is good, I'd rather patch in a spot with pinholes than cut out all the factory spotwelds. Of course you have to use a judgement call on how big a spot it is, how close to the panels edge, how much of the panel is pinholed etc etc.

I've seen lots of guys replace whole quarter panels just because it had a small bad spot at the typical areas, only to have all the seams start to rust because they didn't do it properly and take the steps to rustproof it afterwards. Cut and rewelded seams will always come back to bite you if it's not done properly. And factory metal is always well worth preserving, if at all possible.

All just my opinion, but I've spent a lot of years around a friends bodyshop, and he's restored at least 30-40 cars over that time.

[wowens]

Jay's icepick method !  Jab at it like you are chipping ice. If it goes through, replace.  Cut out 1/2 to 1 inch extra to make sure your at solid metal. If your not proficient enough to but weld and metal finish, overlap 1/2" or so, drill 1/4 or 5/6 holes around perimeter and puddle weld the patch panel in.
Most critical part of a lap joint repair is "weld thru primer". Clean both sides of patch panel and side of floor you are welding to then apply 2 coats of primer to the two surfaces that touch. Clamp and weld. The weld thu primer will liquid, run away from the heat then flow back to the weld when cooling and seal the joint. Grind, epoxy prime, seam seal and paint. No rust ! 
Worth industries makes the best, 3M is also good.
48 years collision work.

[JERICOGTX]

If the floor has a hole, AND if a FULL replacement panel is available, THAT is the way to go. I don't care for 1/2 panels, or sections. Can they work? yes, but I'm a detail freak, and BOTH sides need to look correct. patch panels always look like crap to me. Just my opinion.

[drdano]

Did the pick method around the spots where there were rust holes clean through and those were the only areas the pick went through.  Once I moved an inch or two away from those spots, the pick wouldn't go through.  The drivers floor picture attached looks bad, but underneath really the only areas you can tell it's rotted through are the rust holes, along the spot weld seam from the trans tunnel to the frame rail at the toe board and the body mount hole at the lower left of the picture.  The rest from the bottom looks ok, but the top looks....not great, but maybe I'm just judging too harshly due to the surface appearance.

AMD makes a very nice reproduction floor pan.  I've already had to raise my trans tunnel 2" because the car sits so low, the TKO600 trans and getting all the driveline angles where I wanted them.  So, the repop pan if I went that route would have to get the tunnel cut out of it at a minimum.  It's also going to be near $700 delivered for that pan, which I sorta cringe cutting up immediately.  Maybe it's the best solution, I'm unsure yet.  That's the purpose of the post, to get some guidance and I'm thankful for you guys chiming in and sharing your experience.

[RustyCrankshaft]

Some of this depends on the level of finish you want as to which method you use. If you're going for concourse correct, or just a REALLY good resto or good enough. The replacement floor pan is still worth while to use to cut up for making patches with, it saves a lot of time and matches all the contours of the original floor but convenience comes with a price. Butt welded and metal finished is the nicest looking, a lap or flanged lap joint is strongest when done (read sealed) properly. That's essentially how the floor pan is attached at the perimeter from the factory.

Replacing the entire pan is the best solution, but it's a lot of extra work for little to no gain unless it's going to Pebble.

Weld thru primer and good seam sealer (preferably a 2k, but a good quality 1k is fine too) is critical as is good primer. There may be newer stuff available, but DP40 was a hard act to follow. We have gone through thousands of gallons of DP40 here while it was still legal to use.

[TomP]

I wouldn't replace the whole floorpan for that bit. A piece can be bought or made from Sheetmetal the right thickness to fill just the mininimal piece cut out. Cut the patch piece just a bit larger than the rusted area, overlay it and mark around it then cut inside those marks. That way you can trim the patch down to fit with no gaps. Welder should be hot enough to burn through but do short welds at a time and hammer the panel to make sure there are no gaps as you go. This keeps from needing to weld upwards from below. Welds can be ground down and it will look like original.

[Heo]

If you make patches and but weld them, make the corners rounded
to minimice warping