View Full Version : Mustang floorpan advice requested


07-01-2007, 10:05 PM

These pictures are of the driver’s side floor pan of a 1969 Mustang. The car has been in Los Angeles its entire life and has no other signs of rust; the wheel wells, frame rails, doors, fenders, trunk drop offs etc are all original and rust free. The cowl does not leak; however the driver’s side window was inoperable and rolled down, perhaps for a period of years. All evidence indicates that the rust was from the “inside”, not the outside of the car. It appears that there was standing water that pooled at the rear of the back foot well and in the “grooves” of the front foot well. The passenger side of the floor pan is in perfect condition.

It is obvious that I need to replace the rear portion of the floor pan. I have a rust free donor car to cut from, so I can patch as little or as much as I want. I have never dealt with rust repair before and am uncertain how far I should go, with several specific questions and general advice wanted.

1) From the pictures and evidence, the water pooled away from the seat platform. Should I drill out and remove the seat platform to clean and inspect, or should I just spray inside it with picklex-20 and zerorust?
2) Should I try to replace just the indicated portion of the front floor pan? The area above the frame rail has minor pitting. Is it better to leave the factory welds to the frame rails intact and just wire wheel the pitting, picklex-20 it, and coat it with zerorust? Or should I replace the entire floorpan on the driver’s side?

I am torn between wanting to leave as much factory metal and welds as possible and wanting to totally eradicate any traces of rust. If I wire brush/sandblast the pitted areas and treat them with picklex-20 and zerorust, will that really last or am I just going to end up performing the repair again? I intend on keeping this car a while…

Thanks in advance,


P.S. You will probably want to view the large versions... click on the links.

Front floor pan:
Large version (http://forums.vintage-mustang.com/files/attachments/1183344896-frontpan2.JPG)

Rear floor pan:
Large version (http://forums.vintage-mustang.com/files/attachments/1183262109-rearpan2.JPG)

07-02-2007, 12:35 AM
The donor car has the seat platform too, right? if so, Id cut out the whole drivers side floor and replace it as one piece, and eliminate ALL the rust, especially since you have a donor car to use. I hate using repro metal cuz its usually much weaker than original, but since its from a donor car, ya might as well use as much as it takes. Thats just my 1½ cents worth....

07-02-2007, 08:00 AM
Another issue with repro metal is the beads and grooves are usually not as crisp as the original.

Early Ford repro sheetmetal is quite bad in this area.

07-02-2007, 11:53 AM
I would suggest blasting the area and see how bad it really is. Rust can be deceiving. Then decide what to do. Picklex-20 and zerorust are great products and can be used to make lasting repairs. I use it on lots of things as long as the metal is not rusted all the way through.

07-02-2007, 12:23 PM
How concerned should I be about drilling out the spot welds on the frame rail extensions? This is a fastback, will removal of the entire driver's side pan require bracing?

Thanks again,

07-02-2007, 01:00 PM
Id try to chisel em out with an air chisel or grind em off, to keep from drilling into the frame so much. Im not sure about the bracing but if ya mean to keep it square, it shouldnt need any. But Im more familiar with F-bodys than Mustangs, so maybe a Mustang guru will chime in here soon ;)

07-02-2007, 03:09 PM
Just to be safe you could get a set of subframe connectors to brace everything up. You will probably want to use a spot weld cutter to remove the spot welds especially on the donor sheet metal. Don't use an air chisel to remove the spot welds, it will distort the metal too much. You can use it to do your rough cut out of the old floor pan. If you are careful with the spot weld cutter. The panel will "pop" loose with no distortion at all. On the frame rails be careful to not cut too deep. After the panel is removed if there are any spots that you cut too deep just weld them in. Then clean up the surface of the frame rail with a grinder. Hammer and dolly the frame rail if there is any damage. Spray it with weld through primer and it is ready. Dry fit you donor panel and check the fit. Take your time to make it fit well. Make sure all the spot weld holes line up. They might not. Weld close any that don't and grind them smooth. Strip the panel and coat the areas that will be covered by brackets/sub frame etc. with weld through primer. Carefully weld the panel back in. You will need something to put pressure near the area that you are welding because the panel will try to warp up from the frame rail from the heat of welding. I use an old hammer handle. I also keep a body hammer handy to tap down the welded area while it is still hot if I have to. Don't weld to many spots in the same area at one time you don't want to get the panel too hot. This takes a lot of patience but just weld a few then take a break. I can post some pictures of the whole process if you're intersted. This is longer that I meant. I kind of got on a roll:D

07-14-2007, 06:06 PM
Absolutely no need for bracing if all you're doing is what is pictured. On the front pan, take a large screwdriver and see if you can punch it through the metal all around the area that you have outlined. If the screwdriver doesn't go through, it doesn't need replaced. That would leave you with just doing a spot repair where the pinhole is. On the rear pan, I would cut midway between the end of the ribs and the seat riser, and cut along the top of the foot well and around the torque box. Don't make it harder than it needs to be. Good luck.

Ted Young
08-05-2007, 09:28 PM
Hi - I'm working on a '69 Mach 1 myself. You won't have to worry about bracing if you drill the spot welds out that attach the floor pan the the frame rail.

Currently, I have the lids off of the torque boxes and the driver's side floor pan removed.

Subframe connectors - if you are really worried - may be good to pick up now if you plan on installing them in the future anyway.


09-07-2007, 12:25 AM
The front floor pan does not look too bad but I would drill out the spot welds on the platform and check the condition of the floor pans. If you decide to use spot weld cutters (they work well) becareful to keep the cutter strait. most cutters look like a small hole saw and the blades break easily. Personally, I prefer a 3/8 drill bit. Drill bits are reasonably inexpensive and I found they work much better and faster, but thats your call. If you have a donor car I would say dont chop it up o save $35 in parts. Aftermarket sheetmetal is fine but you have to be willing to be patient and tweak it as needed. Your rear pan is a easy fix, just have your new parts before you start cutting away the old pan so you know what you are working with. Good Luck!