E-Bodies.org Cuda Challenger Forum

Technical Shop => Body Shop => Topic started by: Msbaugh440 on February 24, 2019, 06:28:57 PM

Title: Floor pan replacement
Post by: Msbaugh440 on February 24, 2019, 06:28:57 PM
Got my interior pulled apart. The floor pan is in really bad shape, worse than I thought at least. Looks like the whole firewall is good, but the floor pan is pitted too bad in some areas to just sand down and re-paint. I'm thinking about fixing it the right way the first time, using one of AMD's full floor plan replacements instead of butt welding patch panels.  I've gotten really good at welding patch panels, but don't think it will be the best fix for this one, since there's small rust spots both in the front and back of the floor. I have never done a floor pan on one of these things and have a few questions...

Title: Re: Floor pan replacement
Post by: truckinman466 on February 24, 2019, 06:56:46 PM
I don't know about the tranny question but as far as your bracing goes,as long as you are level you'll be ok. I always use weld through primer between the panels. You should seam seal after you get a primer sealer on first. I just did my car firewall to tailpanel. One section at a time, you will be good
Title: Re: Floor pan replacement
Post by: kathyscuda on February 25, 2019, 04:45:49 AM
take it off the jack stands. The suspension will keep it level.
grind the welds around the hump. Remove it. take out the 2 bolts that hold the shifter mechanism. let it hang out of the way.
get your air chisel with the flat blade and start cutting.
Title: Re: Floor pan replacement
Post by: xx88man on February 25, 2019, 05:25:44 AM
The AMD pans fit 71-74. If your car is 1970 you have to leave a flange to weld to. Just thought I would point that out as you didn't mention the year of car you're working on.
Title: Re: Floor pan replacement
Post by: aussiemark on February 25, 2019, 07:07:25 AM
You can get 1970 specific floor pans that fit perfect.
Title: Re: Floor pan replacement
Post by: Msbaugh440 on February 25, 2019, 07:16:31 AM
Ok, leave it on it's wheels, not on jack stands, drill out spot welds on top of frame and flange, remove transmission hump first, make sure I order a 70 specific floor pan as they're different from 71-74, and use an air chisel to separate from flange. Sounds like a good starting point!
Title: Re: Floor pan replacement
Post by: Msbaugh440 on February 25, 2019, 07:23:02 AM
Here's what I've got it down to so far, for the most part there was only surface rust on the firewall. I do not think the floor pan is salvageable with the pitting I'm seeing already.  Leaning towards full replacement but I'm going to grind/sand it down all the way
Title: Re: Floor pan replacement
Post by: Rich G. on February 25, 2019, 10:10:15 AM
I use a disc sander and grinder and ground off most of the metal on the spot welds so when I hit it with the air chisel it popped right off and didn't cut into the frame rails or rockers.
Title: Re: Floor pan replacement
Post by: anlauto on February 25, 2019, 10:18:28 AM
You should strip the car entirely, have the shell media blasted properly, then worry about fixing the rust  :alan2cents:
Title: Re: Floor pan replacement
Post by: Msbaugh440 on February 25, 2019, 12:34:51 PM
I know you're 100% right about that... I should do the entire thing properly, but the rest of the car is in great shape. The floor pan and the trunk floor are the only spots with rust and the paint on the car is still in great shape, so I'm not quite sure I'm ready for the full blown media blast/repaint work.  The car is not an original build, so I'm basically just trying to get it back on the road
Title: Re: Floor pan replacement
Post by: jimynick on February 25, 2019, 08:20:33 PM
It took some finageling to get my AMD full floor in and I had the firewall out at the time. The front flange that meets the firewall flange could be bonded if you can get some clamps in and on it. Failing that, you can weld it together from the inside and seal the outside to keep water out. I wouldn't try to keep that oem floor; by the time you grind away at the rust you'll have it as thin as tissue and you won't be happy down the road. Check the outriggers that weld on the inside of the rockers and carry the sides of the floor. If they'tr iffy, now's the time to buy/fab new ones before you get the floor out. A box of Clecos can also be your friend when doing this and expect to have to "massage" something somewhere- count on it, but it's doable and give 'er a go!  :cheers:
Title: Re: Floor pan replacement
Post by: Mopar5 on March 01, 2019, 09:22:54 PM
My own humble opinion here if the passenger side of the floor pans are good , I would just section the AMD panel for the areas you need only instead of removing the entire side.
Title: Re: Floor pan replacement
Post by: 70 Challenger Lover on March 01, 2019, 10:18:33 PM
I would section repair it too if it's just one area. Butt welding is harder and you will have to clean up welds with the grinder but it should come out nice if you take your time. In the end, probably amount the same effort as replacing the entire floor.

Another route to consider is patching it but overlapping the metal rather than butt welding. You can get away with this method since it's all covered with carpet but you need to use a good sealer at the joints in between the overlapping metal. This will be significantly faster and easier. Overlapping is basically what the factory did at all the seams so it's not considered substandard work. The rear foot wells are panels that are overlapped with the front floorboard.

The hardest part of replacing a floor in my opinion is to get the front edge to seam up nicely with the firewall panel. Doing a section rather that the entire floorboard may be a lot easier to fit properly along this leading edge.
Title: Re: Floor pan replacement
Post by: jimynick on March 02, 2019, 07:20:30 PM
Please, don't section/patch it! While the factory did overlap panels, it was only at the edges where they met and the first sign of a hack job is an overlaid patch. As I mentioned earlier, if the panel is rotten enough to replace in the noted spots, how much behind can the rest of it be? You'll go to all the work and expense only to end up with a substandard repair that will be a philosophical stone in your shoe which will detract from your ultimate enjoyment of the car. I got my bodyman's licence in 1974 and have been there, done that; but in the final analysis, it's your car and your call.  :cheers:
Title: Re: Floor pan replacement
Post by: Msbaugh440 on March 03, 2019, 06:26:48 AM
Woah! Thanks everyone for the advice, but wow, a lot of conflicting opinions!  Don't worry, if I were to section anything it would only be butt welded, no Laps. Turns out I need to put a little more work into this thing though, so I think I'm past the point of sectioning metal in.  Looks like the rear foot well area needs to be replaced on both sides too, the passenger rear foot well already has pin holes after grinding it down some.  All the metal on the sides near the rocker and under the rear seat appear to be in great shape, so I should be able to tie the new floor into good metal. I would only retain the two factory Laps where the stock locations near the front/rear pan overlap and the rear/under rear seat overlap is.
Is there any way to get rid of those lap joints as well?  I'm looking at AMD and looks like I would have to buy the complete front and 2 rear foot well sections separately, correct?

I think entire new metal is the best (and easiest?) way to do it since there's really only plug/spot welding to do. I'm going to have to finish stripping the entire interior and looks like the transmission and drive shaft are going to have to be removed as well for this job. Sounds like I'm ok cutting it out with it on it's wheels, but I'm seeing different opinions on bracing as well. I do have sub frame connectors so that should help with rigidity. 

I bought a nice Blair spot weld cutter and an air chisel so that should hopefully get me started.

Title: Re: Floor pan replacement
Post by: Msbaugh440 on March 03, 2019, 07:00:22 AM
Will I be able to get a full floor pan in through one of the doors? Am I better off getting something below which has the front and rear all in one piece (this was on classic industries website), or getting the separate panels from AMD?
Title: Re: Floor pan replacement
Post by: Msbaugh440 on March 03, 2019, 07:03:53 AM
Here's the AMD options. I'm guessing I would have to butt weld the two rear foot well panels together, and then lap the front and combined two rear panels together.
Title: Re: Floor pan replacement
Post by: anlauto on March 03, 2019, 10:07:00 AM
I highly doubt, or would be extremely surprized if Classic Industries sells the three pieces welded together like that. :thinking: The picture is wrong or they're just showing how they go together. :alan2cents:
However, I've been wrong before.
Title: Re: Floor pan replacement
Post by: 70 Challenger Lover on March 03, 2019, 01:42:23 PM
They probably don't come together. The factory designed the rear foot wells to over lap each other in the middle and also at the front main floor panel. There won't be any butt welding if you do entire pieces like that.

I think putting in just a front should go in by itself but I only patched a couple areas of mine so someone else will want to verify this.
Title: Re: Floor pan replacement
Post by: jimynick on March 03, 2019, 06:25:31 PM
"I bought a nice Blair spot weld cutter and an air chisel so that should hopefully get me started."- good for you! You can buy short, double ended 1/8" drill bits and I'd drill a dimple in the middle of the spot welds to keep that Blair cutter from catching an edge and skipping all over. They also sell some neat 1/2" belt grinders these days and they're the hot set up currently to grind through the upper layer only. A few Clecos will come in handy when laying out your replacement panels. I replaced the front floor and firewall on mine and used a bonding adhesive as a seam sealer which will give you adhesion and waterproofing in one bite. Good luck and, if you haven't already discovered it, don't be too surprised if you find even more rot the deeper you get into it.  :cheers:
Title: Re: Floor pan replacement
Post by: aussiemark on March 03, 2019, 07:32:34 PM
I went under the car and drilled holes to mark the cross members then just cut it all out with a cut off disc and was left with strips of floor spot welded to the cross members, inner rockers and floor supports/outer seat mounts. Then mark all the spot welds and carefully grind them down and pull the remaining strips off. I also don't think that Classic industries floor pan comes like that because it will not fit in the car, the full front floor just fits as it is.
Title: Re: Floor pan replacement
Post by: Msbaugh440 on March 03, 2019, 08:34:10 PM
Awesome! Thanks for the help guys! I bet you're right, I'm going to end up with a full restoration by the time I tear this apart!!! Lord Knows id love to fully media blast and re-build it, but it would be 5 years before I'd be driving it again and would probably be the end of my marriage! :(

I already know that my trunk pan needs to be replaced and one of the trunk extensions has rust... I just don't want to destroy the paint job (it looks great but is obviously hiding some bad stuff underneath). It's an all original body that's only had minor work and a re-paint, never been fully restored. Other than it's a slant 6 that I've put a 440 in!

I just got into body work, I'm no expert, but I recently fixed a lot of rot in an older Cummins truck and feel pretty confident in my welding/fabrication skills.  We'll see where this goes, maybe I should start a restoration thread...
Title: Re: Floor pan replacement
Post by: Msbaugh440 on March 03, 2019, 08:40:12 PM
Quote from: jimynick on March 03, 2019, 06:25:31 PM
"I bought a nice Blair spot weld cutter and an air chisel so that should hopefully get me started."- good for you! You can buy short, double ended 1/8" drill bits and I'd drill a dimple in the middle of the spot welds to keep that Blair cutter from catching an edge and skipping all over. They also sell some neat 1/2" belt grinders these days and they're the hot set up currently to grind through the upper layer only. A few Clecos will come in handy when laying out your replacement panels. I replaced the front floor and firewall on mine and used a bonding adhesive as a seam sealer which will give you adhesion and waterproofing in one bite. Good luck and, if you haven't already discovered it, don't be too surprised if you find even more rot the deeper you get into it.  :cheers:

Those belt sanders look awesome! I've got to have one! Any brand you recommend?
Title: Re: Floor pan replacement
Post by: jimynick on March 04, 2019, 07:56:48 PM
The industrial ones are stupid priced, but Harbour Freight has one for $38 that seems to have a bunch of good reviews, so who knows? Buy a good supply of belts when you get one as they won't likely be available at Home Depot. 60 and 80 grit would likely do it.  :cheers:
Title: Re: Floor pan replacement
Post by: aussiemark on March 06, 2019, 02:11:47 AM
I found the belt sander useless belt kept tearing and flinging off, the spot weld drill bit was the best way.
Title: Re: Floor pan replacement
Post by: 70 Challenger Lover on March 06, 2019, 05:46:51 AM
Quote from: aussiemark on March 06, 2019, 02:11:47 AM
I found the belt sander useless belt kept tearing and flinging off, the spot weld drill bit was the best way.

I personally found the angle grinder to be very effective. They are $10 on sale at Harbor Freight so you can lean into it and give it the abuse. If the top panel is being replaced, I try to drill with a standard 3/8" bit but only deep enough to touch the panel underneath. Then a cold chisel usually pops it free. Never had great luck with spot weld cutters. I alternate between drill and grinder depending on available space. Someone else mentioned a good idea that I also use. Trim away all metal leaving only the areas that have welds. Easier to work with and provides more room. As you start down a strip of spot welds, use a cut off wheel (fits on a second $10 grinder) to remove strips already freed. I also cut in between every two welds so I can use pliers to twist the piece loose in addition to cold chiseling. Once you find your groove, it's dirty work but you can remove a floor or an upper cowl in an hour or two.
Title: Re: Floor pan replacement
Post by: RUNCHARGER on March 06, 2019, 07:11:54 AM
I feather them with an angle grinder or zip wheel on it's side as well. I try to grind it paper thin without touching the base metal and then pry the remains off. It's whatever the individual feels most comfortable with for sure. I usually air chisel the big chunks away first so I can finnese what's left.
Title: Re: Floor pan replacement
Post by: 70 Challenger Lover on March 06, 2019, 07:30:50 AM
Your method is probably ideal since you don't disturb the base metal. If I can accomplish that I'm happy as I just take an angle sander to it afterward and clean it all up.