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Background: My original doors were too rusty to fix, so I bought a pair (no rude comments, please;-). They are in much better shape, but I want to insure that rust cannot get started again. They were sprayed inside with a tar like coating, which thoroughly protected areas that would never rust anyway, and missed areas where it might have done some good. I've removed all of this old goo, and I'm left with original primer mostly, some bare metal, some surface rusty metal.
Question; what can I use to thoroughly coat the insides of these doors? There are areas that cannot be reached by brushing or spraying; either to prep the surface or to apply a coating. Dipping or sloshing the inside (like a gas tank) is the only way I can think of to get at the entire interior surface. The material would have to be thin enough to get into the nooks, crannies, and inaccessible areas, and sticky enough to adhere without perfect surface prep. Obviously, it doesn't have to look good, just work. Any suggestions? Rodney
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Good advise above. I like to increase the size of the drain holes with a file to about twice there original size. Then seal bottom door skin fold from the inside with body caulking. It's very important to keep the water out of that joint. Dont forget the cavity wax after the other treatments, rattle can type is fine.

UFO-LOW I feel your pain. Guys that are lucky enough to not have humidity just would not understand....

I would throw in a suggestion into the ring too. Use the stuff that BMW and Mercedes uses in their vehicles -- it is not a paint or an undercoating that you are familiar with. It is more of a waxy material that never gets hard. It creeps and crawls when you install it so it gets between seams and into any area that is spot welded to stop any exposed metal against the dreaded rust tin worm. Wurth makes a great product that the major OEM's use; and it is here:

Wurth Body Wax

Best of luck on your project!

Originally posted by garth66:
I just did this to my inner chassis frame rails, suspension mount points (horse shoe area), and body seams in the front of each rear quarter (behind the gas tank) and against the B-pillar (back of door jamb).

Tonight I'll post what I did and how I did it.

So here's what I did...

Follow Jack DeRyke's excellent article on this upgrade/TSB. Can be downloaded here:

Added an additional drain hole at the bottom of this structural frame member to insure any moisture that got in here would easily drain out.

I enlarged the factory drain holes at the base of the vertical frame structure in the rear wheel house, and added 1/2" drain holes in the lower frame rails per Jack DeRyke's article (downloadable above).

I made a simple spray apparatus with a $6 sprayer from Home Depot, some 3/8" hose, a couple of brass fittings to secure the hose to the sprayer, and a fan spray tip from an old weed sprayer that no longer works.

I then sprayed the inner frame rails with Jasco Metal Prep which converts rusted rust from ferrous iron to iron phosphate and prepares the metal surface for paint. The Jasco costs about $6 at Home Depot, which is a far bit less expensive than the same designer label products from Eastwood.

To apply, I would insert the spray tip into a frame rail as far as it would go, then spray while slowly pulling the hose back to assure complete and even coverage of all interior surfaces. Do this in both directions from each side where you have access. I inserted the spray hose up into the wheel house horse shoes from the engine compartment side and performed the same procedure on both sides.

CAUTION: This product is acid-based, is a skin irritant, and will etch concrete. Be sure to wear gloves, goggles, and put a plastic tarp under the car!

I then applied Eastwood's "Rust Encapsulator" to protect against any future corrosion. Here's a picture of the area behind and in front of the gas tank after treatment, This area is notorious for rotting through from the inside since dirt, gravel and moisture all get trapped between the gas tank and the body panel.

Last edited by garth66
FWIW, Eastwood also offers an Inner Frame Rail coating kit which admittedly would have been easier than fabbing my own sprayer, but at $20/can I thought the price a bit steep.

Now my sprayer is available for any other local Pantera owners to borrow who want to do the same thing. Might just have to have a rust-proofing tech session soon.

Either of these processes would work for coating and protecting the inside of the doors.
Last edited by garth66
Hi Garth,
thanks for the pictures and info, I was wondering where the ones in the frame rails were supposed to go. However I have one question - I drilled holes in the uprights in about the place you have the small ones - ca. 1/4 inch or maybe 5/16 in diameter, can't exactly remember now. Anyway I immediately felt guilty about them being too big - don't you think that having ones as large as in the photo weakens the bottom of the upright too much?
Cheers, Tim.
don't you think that having ones as large as in the photo weakens the bottom of the upright too much?

FWIW, the holes in the bottom of the inner wheel house horse shoe are only 3/8". I don't feel they weaken the bottom of the area because the steel there is very healthy on my car, and I believe most of the strength in the structure comes from the edges and corner/bend in the channel. The hole in the middle of the 'field' does little to reduce the strength. Similar to lightening holes being drilled in race car chassis' which don't compromise the integrity of the structure. Likewise with holes for plumbing and electrical drilled through the 2x4's used to frame your house - no adverse structural impact if they're not on the edge of the 2x4.

Also note in the first picture the VERY LARGE hole above the small hole I drilled. This large hole is original from the factory and doesn't compromise the integrity of that structure.

One last thought. I've inspected several Panteras that had only the small factory drain holes that were so clogged with dirt, gravel, and crud that the surrounding steel was completely rotten - one car I could push my bare finger through the steel. Now THAT weakens the bottom of the horse shoe (upright) much more so than an adequate drain hole!

Last edited by garth66
In the UK where climate and salted roads mean cars last about 5 minutes we always used Waxoyl in the frame rails and internal panels. It is a oil coating that you spray into the frame rails and the light paraffin component evaporates to leave a wax coating. It is available in the USA, but I'm not sure if these new products are a superior system.

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