Nice post, I'm in the middle of doing just that, a complete roof replacement on a 78S/C that I should have junked but I'm now in too deep to turn around now.

 

do you know if the 67-72 are the put together the same way?

 

Hmm, Interesting. I've been around a lot of these trucks and I've only seen one rusted there. It was on a red & silver truck where the silver wears away so it was down to bare metal.
Is this is bigger problem then what I've personally seen? Where you are saying the rust starts, whats the best way to rust proof that area? Just pull the head liner?

 

This is more of a problem with crewcabs than regular cabs. Pulling the headliner will allow access to spray.

Nice drawing/write up F-800

 

My drip rails are rusting on my supercab. The rest of the roof is fine, actually no other rust anywhere on the truck.

Any way to fix it beside cutting the roof off?

 

Nice post! I've never seen a section through that area before.

 

i have looked at quite a few, but havent actually cut a 67-72 apart in that area. I would assume that they are constructed similarly, but dont quote me. Maybe someone can confirm...

 

My theory is that water condenses on the underside of the roof in humid climates and runs down and collects behind the driprail and sits. (I had my headliner off and windows cracked during a foggy night, and had water raining down from the inside of the roof). It also can enter through the driprail from the outside if the original sealer is cracked.
Pull the headliner, spray Heavy duty anti rust, por 15 or what ever you can get in there.

 

If you have rust all of the way around, I don't see what other choice you have. If its just a small area, just replace that spot. Avoid making butt-welds on the 73-up roof skin as it is very difficult even for a professional to do on the thinner metal. (that is why replacing the whole roof is likely faster and easier than fixing your old one)

post some pics, maybe i can advise on your super cab.

Supercabs seem to have a problem with rusting the vertical part of the driprails. I would use a spotweld cutter and remove that section if it is bad as removing the roof for those sections is not necessary. Or if it looks solid enough, clean the area up with a brush attachment on an angle grinder (delicatly), then treat the area with rust converter, getting it in the seams. If the horizontal part is bad, refer to the schematic.

 

Thank you.

Crew Cabs allow outside air in via the rear door hinge pockets, up through the B pillar, and across the roof. Regular cabs are relatively sealed from the outside.

 

Excellent diagram!!! I will be up against this same problem on my crew...only rust on the entire cab is the drivers side drip rail area....Can a regular cab or supercab roof area be used for the repair patch panel??

 

It could but like F-800 mentioned the metal is so thin it makes it tough to weld. When I welded the patch panel on the lower part of my rear door I was chasing holes for quite a while.

 

The part thats rusted is where you described just on the vertical part of the drip rail.

As there is no other rust anywhere else on the truck I started thinking that water may be entering through the old dried out cab light seals and running back.

 

It's possible. My truck (regular cab) was sold new in FL and stayed there for quite a while. I have major rust on and under the drip rails, but the rest is solid. It's baffling.