roof rust

[oldfordnut]

ok i have a 71 f-100 and the roof aroud the water retainign thing drip rail whatever it is called is all rusted under it does anyone kno how i could fix this how to get it off and pacth it anywyas let me kno thnx

[fordman]

how bad is it ? do you have a pic? is the rail rusted or the roof it self? is it all the way through?

[BigRedTruck]

I had the same thing and put some sort epoxy in until i get around to fixing it. I believe it was redline gasket...something something...that stuff you put between engine parts. a shop i took it to said they would have to take out all the current caulking and weld it, then replace the factory sealent. at one spot mine was leaking all the way through. It felt like a sub when it rained...highway speeds = water jet.

[FORDification]

First of all, let me try to explain how the roof rust gets started in the first place.

The roof panel is a separate piece which is spotwelded along the drip rail area. Here's a very basic diagram of what it looks like. The front edge of the roof panel actually has a small lip on it that fits down into the drip rail...it's this lip that is spotwelded onto the drip rail:



The factory then coats the inside of the drip rail area with caulking to seal up that seam. However, over time the caulking starts to crack and lift away from the metal. Moisture then gets down into the cracks, underneath the caulking, where it just sits and starts to eat away at the sheetmetal. Here's a view of the caulking on my '67 before I started stripping it down. This truck only had 29K miles on it and you can see it's already cracking.



And here's a picture taken after I stripped out the caulking. You can see how rust is forming on the driprail area and the front lip of the roof panel. You can also see the spot welds. Now look closely...when moisture gets down in here, it can actually get in-between the spotwelds and into the cab. Once it gets into the cab, that's where the real damage is greatly accelerated.



What compounds the problem is how moist air can enter the cowl vents, travel up through the hollow roof pillar and into the dead air above the headliner. Because there's very little air circulation there, the moisture just sits there. It condenses on the inside of the roof panel, where it then runs down to the lowest point, which just happens to be the roofpanel/driprail seam on the inside. So now you can see how this roofpanel/driprail seam is actually getting attacked from both sides by moisture, until this is what you end up with:



The way for us truck owners to combat the problem is two-fold:

1) Remove the headliner to gain access to the top of the windshield pillars. Seal off the pillar somehow with expandable foam or something similar, to prevent moisture from entering the cab interior above the headliner. Clean out the seam area (where the roof panel connects to the windshield surround) and coat it with POR-15 to permanently seal it.

2) Regularly inspect the driprail caulking. As soon as any cracks are noticed, you need to completely clean all the old stuff out and replace it. If you can get the driprail area COMPLETELY cleaned out, it might be a good idea to put a coat of POR-15 down there to permanently seal it. Then you can reapply the caulking for a factory appearance.

OK...now onto your original question. The only real way of repairing rust is to cut it out and weld in fresh sheetmetal. However, because of where the metal tends to rust and how the cab is assembled, it's going to be a major job to do. Before I found my present almost-rustfree cab I was going to attempt to do this very thing, and you can check out what I was doing on Page 18 of my project updates. You can see that it's not an easy job. Fortunately I found another cab to use before I got any farther into that task.

To be honest with you, you would probably have less time/money invested by finding a different cab. Even if you only had access to a parts truck with rotted floorpans and/or cab mounts, repairing these areas is MUCH easier than trying to tackle the roof rust itself. Welding on a whole roof panel, while trying to keep everything lined up, isn't going to be fun at all.

If this is something you DO want to attempt, it just so happens that I still have the patch panel I cut out from a donor truck. It's been sandblasted and ready to weld in.

[1970F250]

mine was really bad and i just cut the roof off and put one that i found in the junk yard on it.

[flyboy2610]

Thanks for the info about the door pillars, Keith. I didn't know that!

[rjewkes]

me neither. I thought it was only getting it from outside. But if you block it at the top around the problem area do you not cause a different rust area? Say the pillars and or cowl?

[rjewkes]

oh ooooooooooooooooooooooh ooooooooooooooh. Just had a though waht about just fnnelling a lot of poor 15 in there? or that special wand extension up there with por 15?

[FORDification]

By sealing off the roof pillar you'll be eliminating a majority of the moist air completely. By sealing it at the top, any moisture which attempts to enter the pillar will condense and run back down the pillar and out of the truck, never entering the cab in the first place. Coating the pillar walls with POR-15 isn't going to help. Not only does the pillar not rust out (since water can't just sit there) but moist air can still enter the cab, although now it's trip up through the pillar will be through a nice shiny-black conduit.

Combating rust in the cowl area is another unrelated topic. That's mainly done simply by keeping leaves and pine needles cleaned out, and making sure the drain holes are kept unclogged.

[rjewkes]

And that is why you are Admin. You know how to answer the questions i forgot it had no where to sit in the pillar.

[adam138]

If I clean out my caulk in the driprails what kind of caulk,or whatever should I use to refill it?

[FORDification]

Any auto parts store should be able to get you seam sealer. You can get it in a brushable form or in a caulking tube. The tube-type is probably easiest to apply...after running a bead of this across the drip rail, just run your finger along the bead to spread it out and form a channel. Normally this stuff dries in less than an hour so it can be painted (if desired).

However, the factory used a self-leveling type of sealer, which is why it's usually flat. 3M makes a good self-leveling seam sealer

[adam138]

ok thanks alot

[CACWBY]

I had the rust cancer on passenger side, though not as bad as Keith's picture, and the bodyshop felt it would be less time (and therefore less $$$) to shave the drip rail completely and repair the affected area with a welded in patch.

There wasn't much evidence prior to stripping paint, just a little "bubble" type thing in the paint on the roof corner behind the drip rail. Paint covers a lot of surprises!!!