So I started tearing into my latest car. The bottom of the passenger long is rusted, but the top is not. I always assumed if the bottom rusted, it started from a hole in the top. The only thing I can figure is, water leaks through the seam behind the battery tray? The top of the long in this car is pretty clean, no holes at least.

Any tips on repairing this location?

Click to view attachment

Click to view attachment

I looked at a car today that was the same way. Battery box area was solid and the jack post came out when I pulled the post plug.

Car was rusty around the windsheild but the pans were solid. Also the hood and deck lid were toast.

Kind of werid to see one not rusted in common places

You never know about these cars.

Condensation inside the long. Cold metal, moist air then warm air from the heating tubes.

Tall wet grass is a another source of uni body rust issues

You may have had some of that inner wheel well holing starting before you pulled off the battery shelf, where battery acid & water combined to get down into the long. There's also a drain hole in the lower left of this bottom pic of yours where moisture can get inside the long, as well as tiny gaps in the sheet metal seams - the heater tubes in the longs can also crack &/or have gaps, leak warm moist heater air, which then cools & condenses out the moisture inside. Then it just sits on the bottom & does its nasty work!

Would drilling holes in the longs and installing drain tube similar to the ones in the headlight buckets be effective or a source of more water to get in ?? Anyone tryed this , or is it a really really bad idea ?? Just curious as to a way to get moisture out, if at all possible.

Jack / Jaxdream

Also there are vent holes in the seam at the bottom where the sides come together in the spotwelded flange. If a owner washes the dirt from between the rocker and the long but sprays up on the bottom of the long the watergoes in the drains and sets on the floor of the long.

Yep i forgot about them . Maybe using a air hose and blower attachment occasionaly would expell some of the moisture , or simply divert some of the warm air from the heat system back into the long channel giving a positive pressure to the long area, maybe still bad idea . Oh , well ....

Jack /Jaxdream

I think it leaked at the seam where the long meets the outer wheelhouse. That seam is kind of wide. At least wide enough for water to get into.

At what point do I need a new outer wheelhouse? I am planning to work with what I have.