Muscletang needs new floor pans - advice?

Help Support 7173Mustangs.com:

Joined
Aug 14, 2014
Messages
3,550
Reaction score
500
Location
Madison, WI
My Car
1971 M-Code Mach 1 w/408C stroker
I knew there was a surprise waiting for me under the carpet. However, this is a bigger surprise than what I was expecting. With winter fully here I started my investigation of the "guts" of the car. I have not found rust anywhere except the floor pans and bottom of firewall as shown in pictures. When the car was restored they did what appears like a horrible job of repairing the floors. There is fiberglass on the floor over the pans. Off course, over time the rust continued and as you can see in the places where I removed the fiberglass there are areas where the pans are thin. I made most of the holes while poking with the screw driver. The rear floor panel on the driver's side is the only one that looks "solid," but I assume I am better off just replacing the full panels on both sides.

I have been reading the threads about how to repair and although it seems a lot of work, it looks very doable and reasonably priced. I am looking at this floor pans, http://www.cjponyparts.com/floor-pan-full-length-1971-1973/p/FLP4P/

Welding aside, is that all I need? These pans seem to have a little of firewall, but I don't know if I may need more due to the rust, thoughts? Also, how much of vertical wall do they have at the edge that meets the door frame? I am concerned on how much should I cut away.


Note fix of the seat mount threads on driver's side rear-left bolt.

Bottom pictures show a patch of fiberglass and a close-up of the panel where the seat connects. I was not able to read what it says.

20141129_235427_resized.jpg

20141129_235458_resized.jpg

20141129_235509_resized.jpg

20141129_235544_resized.jpg

20141129_235557_resized.jpg

20141130_000251_resized.jpg

20141130_000408_resized.jpg

 
Last edited by a moderator:

guys72Mach1

VIP Members
Joined
Mar 24, 2012
Messages
248
Reaction score
5
Location
Eagle, Idaho
My Car
1972 Mach 1
1969 Bronco Sport
1964 Falcon
Mine had similar area's of rust and even worse on the passenger side(due to the fresh air intake rotting out). I ended up buying both sides full pans, then cut them up accordingly. I wanted to utilize what ever existing good metal that was there, but definitely wanted to cut out any cancer and area's of suspicion.

It was a job, drilling, spot welding, seaming, floating out, sealing, then spraying the sound coating, but well worth the effort.

For me, it was better to cut the rear pans in sections and use what I needed, then to use the one piece compete drivers pan/passenger side pan.

 
Joined
Aug 14, 2014
Messages
3,550
Reaction score
500
Location
Madison, WI
My Car
1971 M-Code Mach 1 w/408C stroker
I was wondering if i should skip the step of removing the seat base pan (name?). Is there a reliable way to inspection the pan underneath? As far i can see through the holes it looks good.

I dont want to go through all the work of drilling it out and then find out it is in good shape. Or is it simply nonsense? Since i am there i should replace as well.

1971 M-code Mach 1

 

cudak888

VIP Members
Joined
Jul 21, 2012
Messages
3,240
Reaction score
16
Location
South Florida
My Car
'71 Mustang Mach 1 M-code "Soylent Green"
'69 Plymouth Valiant 100
'68 Plymouth Satellite
I was wondering if i should skip the step of removing the seat base pan (name?). Is there a reliable way to inspection the pan underneath? As far i can see through the holes it looks good.

I dont want to go through all the work of drilling it out and then find out it is in good shape. Or is it simply nonsense? Since i am there i should replace as well.
Definitely remove the seat risers - you'll probably find floorpan holes under them as well. Make sure you take out your fuel line too, or you're almost guaranteed to grind through it when chopping out the driver's side pan.

This might be an ideal job to use 3M 8115 panel adhesive to adhere the panels at the overlap/lap joints. You could probably use it on the pans too, but the spot weld holes will look ugly if not filled up with weld.

-Kurt

 
Last edited by a moderator:
Joined
Aug 14, 2014
Messages
3,550
Reaction score
500
Location
Madison, WI
My Car
1971 M-Code Mach 1 w/408C stroker
Last edited by a moderator:

MACH 5

New member
Joined
Sep 18, 2014
Messages
3
Reaction score
0
Location
Chicago
My Car
71 Mach 1, 351Cleveland, C6,

66 Convt Shelby Clone, 340 stroker, Cleveland Aussie heads, B & A Intake, Holley 750, AOD, Currie 3:50 rear end, Disc all around.
:dodgy:go ahead with the floors, just make sure the inner and outer rockers are fine . if those are rotten you need to them first and they are tricky. Mach 5

 

guys72Mach1

VIP Members
Joined
Mar 24, 2012
Messages
248
Reaction score
5
Location
Eagle, Idaho
My Car
1972 Mach 1
1969 Bronco Sport
1964 Falcon
These are the pans I first looked at, http://www.cjponyparts.com/floor-pan-full-length-1971-1973/p/FLP4P/

but they also have the Dynacorn's, http://www.cjponyparts.com/dynacorn-full-length-floor-pan-coupe-fastback-1971-1973/p/FLP5P/

The later are $30 more. Any experience with either? CJ's offer expires today so I would like to order today.
I went with CJ's also. They weren't exact in all of the stamped patterns, but the shape was right on. When it's all said and done, know one will ever know, or even recognize the difference.

You can always give it a good whack with a metal hammer and listen to the sound. If it sounds dull, good clue that it needs to be replaced. Old school metal worker habit....

 
Joined
Aug 14, 2014
Messages
3,550
Reaction score
500
Location
Madison, WI
My Car
1971 M-Code Mach 1 w/408C stroker
I guess that if I needed a little bit more metal on the firewall I could use any piece of straight panel beyond the floor pan edge.



This might be an ideal job to use 3M 8115 panel adhesive to adhere the panels at the overlap/lap joints. You could probably use it on the pans too, but the spot weld holes will look ugly if not filled up with weld.
Kurt, if I understand your comment, are you implying to adhesive bond all the panels rather than welding them? I was under the impression that the panels had to be welded to the subframe square tube running underneath. Is it safe to bond the rest rather than weld? I assume you don't refer to bond the seat riser since I guess it has to be welded due to safety. Can you pleas expand? Thank you.

 
Last edited by a moderator:

cudak888

VIP Members
Joined
Jul 21, 2012
Messages
3,240
Reaction score
16
Location
South Florida
My Car
'71 Mustang Mach 1 M-code "Soylent Green"
'69 Plymouth Valiant 100
'68 Plymouth Satellite
These are the pans I first looked at, http://www.cjponyparts.com/floor-pan-full-length-1971-1973/p/FLP4P/

but they also have the Dynacorn's, http://www.cjponyparts.com/dynacorn-full-length-floor-pan-coupe-fastback-1971-1973/p/FLP5P/

The later are $30 more. Any experience with either? CJ's offer expires today so I would like to order today.
Likely the same tooling. The cost difference makes it a no-brainer; go with Dynacorn so you don't have to worry/return substandard pans.

-Kurt

 
Last edited by a moderator:
Joined
Aug 14, 2014
Messages
3,550
Reaction score
500
Location
Madison, WI
My Car
1971 M-Code Mach 1 w/408C stroker
:dodgy:go ahead with the floors, just make sure the inner and outer rockers are fine . if those are rotten you need to them first and they are tricky. Mach 5
The outer rockers sound and look good. The passenger side seems to have been involved in some type of accident at some point. Look in the picture at how the top of the rockers appears chopped and the inner isn't straight. Because the top is not there I can inspect the interior of the rocker. It was dirty, but no rust.

The driver's side has the top and then some tape over it (bottom picture). I removed the tape since it appears a leftover from when it was painted.

Now I have a question about the passenger side rocker. Is that top piece missing a problem? should something be welded there or it doesn't matter?

20141129_231430_resized.jpg

20141129_231446_resized.jpg

20141129_225627_resized.jpg

 

Qcode351mach

VIP Members
Joined
Dec 24, 2010
Messages
2,888
Reaction score
43
Location
U.S.A.
My Car
1972 Q code Mach 4spd
2004 350z
2005 Corvette
1971 Camaro SS/RS
I have a bunch of vids that will help you with your floor pans...Do not use panel adhesive to replace the floor pans. UNLESS it's just a small hole your repairing.

 

Go Time

VIP Members
Joined
Aug 30, 2011
Messages
663
Reaction score
4
Location
Indiana
My Car
1972 Mach 1
1976 Ford F150 4X4
1994 Caprice Wagon LT1
2004 Ford Focus ZX5
I used the CJ floor pans and they seemed a bit thin to me. Dynacorn may be a bit thicker, but I dont know that for sure. Don from OMS would probably know if there is a gauge thickness difference. I like the adhesive but not on structural pieces. Welding should be done on the floor pans, pretty important piece to the unibody structure. You may consider lap welding the floor pan, its going to be easier than butt welding, but if you want to hide the joint completely from judges or whatever then butt welding maybe your thing its just a bit harder. I butt welded mine with a tig welder but its just because i wanted the challenge. Tig weld joints MUST be tight, Mig weld joints have a small gap to add the wire/filler material so they are a bit more forgiving. I was showing my 18 year old son some tig welding techniques so I thought the floor pan was a great place for him to learn. He is already an accomplished MIG welder. Don't forget to spray some type of coating inside the frame rails and rocker panels. If you weld the floor onto the inside of the rocker panel and do it right you will penetrate with your weld all the way through to the inside and melt any coating that may be "inside" the rocker panel, if there is any in there at all. This will be an unpleasant surprise to anyone who has welded the floor pans to the rocker and in a few years. Eastwood makes an inner frame coating with a 24" hose to get into the hidden areas. Good luck and keep posting Dennis

 

trainey

Well-known member
Joined
Apr 3, 2011
Messages
425
Reaction score
0
Location
Kennesaw, GA
My Car
1972 H-code Mach1
2010 GT Premium
2004 F150- The "home depot" machine
2018 HD RoadGlide Ultra
If your floor pans are rusted out, chances are your cowl(s) are as well. Make sure you inspect those!

 

cudak888

VIP Members
Joined
Jul 21, 2012
Messages
3,240
Reaction score
16
Location
South Florida
My Car
'71 Mustang Mach 1 M-code "Soylent Green"
'69 Plymouth Valiant 100
'68 Plymouth Satellite
I have a bunch of vids that will help you with your floor pans...Do not use panel adhesive to replace the floor pans. UNLESS it's just a small hole your repairing.
Question Q: If nothing else, is it feasible to use the panel adhesive on the area where the pans meet the rockers, as opposed to the rest?

Just curious where the hazard factors in here.

-Kurt

 

73MustangCoupe

VIP Members
Joined
Jul 5, 2013
Messages
958
Reaction score
281
Location
Jonesborough, TN
My Car
1973 Mustang Mach 1
As cudaK888 said in a previous post, remove your fuel lines before you start cutting out floor pans. I'd suggest removing the fuel tank. too, before starting down that road. Also have a big fire extinguisher, or better yet, two, nearby. You don't want to catch your car on fire in the garage. It's a huge, expensive mess. Don't ask me how I know. :(

 

imusa76

VIP Members
Joined
Jun 27, 2012
Messages
3,724
Reaction score
15
Location
Rhode Island
My Car
1972 Mustang Convertable
302 v2 FMX 2.79 rear end
Kurt, I believe the whole floor should be welded, even along the rockers, just because the amount of flex you can get.

 
Joined
Aug 14, 2014
Messages
3,550
Reaction score
500
Location
Madison, WI
My Car
1971 M-Code Mach 1 w/408C stroker
Just a thought.... what about adhesive all around and then spot weld around instead of a continuous bead. However, the heat may damage the adhesive. I have no experience in this field; just trying to stir thoughts.

1971 M-code Mach 1

 
Last edited by a moderator:

turtle5353

VIP Members
Joined
May 15, 2011
Messages
3,435
Reaction score
272
Location
PA
My Car
1971 Mach 1 Mustang
I guess I am adding a welder to my Christmas gift wishlist.

I hear good things from Eastwood's M135: http://www.eastwood.com/mig-welder-110vac-135a-output.html
Make sure you weld the pan in. DONT use adhesive, the floor is a major structural part of the car. If you don't mind seeing the seam, make it easy on yourself and overlap the seams. I butt welded mine and you cant even tell its there, but its time consuming and pretty challenging if you have never welded before. Buy a good spot weld cutter and some bits for it. Also get a cheap flanger/punch tool from harbor freight so you don't have to drill 100 holes by hand! http://www.harborfreight.com/air-punch-flange-tool-1110.html

Watch Q's videos and you will be fine. Its pretty straight forward and easy.

As far as your welder goes, I have had very good luck with my eastwood 175 mig welder. I would recommend the 220volt if you have access to 220 in your garage. Burns in better and can be used for many other jobs if need be. If your just doing small sheetmetal jobs the 110 volt mig 135 will be fine. DONT used shielded welding wire. Its a mess. dirty welds that don't look real pretty. Spend the extra cash and buy a bottle of 75/25 co2/argon mix and use solid wire. Burns much nicer and cleaner.

Take your time and inch up on your final cut. Don't try to get it all in one piece. AS said before remove your fuel line in that area. Take your time and enjoy learning a new skill!!!

 
Top