Best way to 'find' the bad spots is with a body hammer. Use the spike end and give a good hit every few inches. Its a sickening sound when it goes through. We had it punch through both front rails directly between the front bumper supports. If you think that tray was bad design you should see how they built the inner section of the rails between those support holes! *sigh* Instead of replacing the entire rail we simply cut out the bad section, found the rest was fine and welded in some new metal. Cant tell it was done now.

Remember.. if the rust is there covering it will not make it go away. Gotta cut it out or it will spread. Also if its simply a small area its best to find someone to cut it out and replace it now. In 5 years it'll not be a small area anymore.

 

Mine was fine between the bumper support holes. Some rust with a little pitting right under the front of the bumper bracket but it was easy to get it to good metal and clean it up. I did go up and down the rails with the point end of a body hammer last year. Someone, maybe you, had suggested it. It did not turn up any problems. I did not find the tray area problem until I took off the fender to work on them and to clean up the wheel wells. Today, I stripped the front rails from the toe boards to the coil spring down to metal and there was no rust at all there. I found a little surface rust in a few places on the fender apron. The dark areas on the rail are not holes. That's a tar like coating which did not come off everywhere. I'll have to scrape that some more. Strange how these cars can pick places to go to hell.

 

That thick tar crap comes off fairly easily with a heat gun and scraper to start with. Then take Lacquer Thinner and a rag to the remaining crap that didn't scrape off. I did the entire undercarriage and each wheel well of our car from front to back like this and it worked well. I used a wire wheel first and all that did was smear it around.

I had 4 areas on my rails that were bad. 2 small areas on the drivers side rail which were easy to cut out and replace. The 2 others were between those bumper support holes on both sides. The threads aren't welded to the inside of the rail but on a "U" shaped section thats welded inside. Perfect for anything that gets up in there to get stuck between to start rotting it out. Cut that outer section out from front back about 18 to 20 inches and cut out that rusted out inner "U" section. Replacement section has the threaded nuts welded directly onto the plate so nothing to catch crap on anymore.

 

adrenolin, post pics of your progress sometime! id love to see what it looks like

 

I would suppose the only way to replace the "tray" section would be in the engine is out and the shock tower is off, right? I found out about wire wheels and tar early on in the project. Makes a real mess and doesn't take off anything.
I am going to patch the tray area and shock tower for now. Longer term...it would be best to take it all apart and replace everything but that really is not in the cards right now. I've pretty much got it down to clean metal and I did not really lose much thickness outside of the actual holes and the tray area is the only place on the entire rail where there is any problem. I just won't fly it off any ramps like the Duke boys did with the General Lee.

 

put self leveling sealer in that tray, works great, two tubs 1/2 in each, let dry overnight and 1/2 of 2ed tube in each to finsh it off, undercoat it and done $10