Chevy Impala SS Forum banner
1 - 20 of 20 Posts

·
Registered
Joined
·
46 Posts
Discussion Starter · #1 ·
I have 5 B Bodies (4 9c1 and one Roadmaster). One is a New York car and the others are lifetime Texas area cars. All of them are either rotting out or starting to rust in the same location on the top left portion of the passenger floor pan.

Any specific reason this happens? It's not road salt. I want to treat and protect it from happening again but need to pinpoint the source of it.

The picture I'm attaching is from Roadmaster with literally 0 rust, not even surface rust under the floorpans yet it somehow rotted out in the same spot my other cars rust/rot out in as well.

Maybe a constant leak from the heater core or something?
Automotive tire Wood Finger Floor Bumper
 

·
Registered
1995 Cadillac Fleetwood Brougham
Joined
·
2,648 Posts
I have 5 B Bodies (4 9c1 and one Roadmaster). One is a New York car and the others are lifetime Texas area cars. All of them are either rotting out or starting to rust in the same location on the top left portion of the passenger floor pan.

Any specific reason this happens? It's not road salt. I want to treat and protect it from happening again but need to pinpoint the source of it.

The picture I'm attaching is from Roadmaster with literally 0 rust, not even surface rust under the floorpans yet it somehow rotted out in the same spot my other cars rust/rot out in as well.

Maybe a constant leak from the heater core or something? View attachment 202297
It's the "body boxes" that house the body mounts. They are right where the rear of the wheel well meets the firewall.

Why do you say the NY car isn't from road salt?
 

·
Premium Member
Joined
·
8,615 Posts
Water from the AC evap drain. Soaks the entire area. Never know because it's covered by a floor mat usually.
 

·
Registered
Joined
·
8,918 Posts
A big +1 right above.

Plus a big fat untraceable moldy smell for all the poor folks who never find out about the famous "Missing Elbow".
 

·
Registered
Joined
·
46 Posts
Discussion Starter · #7 ·
It's the "body boxes" that house the body mounts. They are right where the rear of the wheel well meets the firewall.

Why do you say the NY car isn't from road salt?
The car in the pic is a lifetime Texas car, that's what I meant by it never saw road salt.

The New York car surprisingly isn't rotted through in that area yet but the road salt did its damage on the rear quarters and the rear wheelwells. The NY def saw road salt. Only 59,000 miles on it though.
 

·
Premium Member
Joined
·
6,816 Posts
Besides ovelapping poorly treated panels , there are a bunch of brackets for heat shields welded to the floor that moisture gets between them and floor pan.
I had to cut all mine off and replace from a doner car when I painted the bottom.
I will check pics tonight
 

·
Registered
Joined
·
8,918 Posts
How do we come about fixing this issue? Cuz I would like to know to prevent this as well?
The drain hole out the firewall often lacks/loses the 5/8" rubber rt. angle elbow and condensate wicks back in under driving airflow pressure into the pan and overflows inside. Best to fit a pc. of plastic tube in the other end pointing down.

For REALLY unlucky guys the drain pan is the culprit:

And there's even word the cowl can leak - but about 1/2% rare.
 
  • Like
Reactions: Lance

·
Premium Member
Joined
·
6,816 Posts
Those pictures , to me is not water in the car .

That said the AC drain pouring down the firewall on the engine side can still be a contributer.
Many of us have extended the drain .
Mine comes out of the bottom of the fender behind the front wheel.

As for the rot , moisture gets inside the many lap joints .

You can see the many overlapped pieces on the outside at the base of the firewall .

My case , the solution was to re&re as many as I could , bead blast, primer , weld back on ,

Active creeping anti rust soaked in is a big help.
Atmosphere Water Liquid Fluid Rectangle
Vehicle Car Hood Automotive tire Motor vehicle
Hood Automotive tire Motor vehicle Automotive lighting Automotive design
Tire Automotive tire Hood Automotive lighting Motor vehicle
Automotive tire Hood Product Automotive lighting Motor vehicle
Hood Automotive lighting Automotive design Car Motor vehicle
 

·
Registered
Joined
·
12,108 Posts
If the urethane that holds the front window in along the bottom fails, water can blow under the window, and ends up on the floor.
 

·
Registered
“91” Oldsmobile Custom Cruiser
Joined
·
310 Posts
I would guess, condensation or a bad/ worn seal from the hvac given the location. It doesn't look like a serious leak, but it must be constantly wet enough to eventually eat a hole through the floor. Considering our cars are at least 26yo, everything that can happen to them has likely happened to at least some of us. I would just fix the hole, add some kind of rust inhibitor and not worry about it for another 25+ years.
 

·
Registered
1995 Cadillac Fleetwood Brougham
Joined
·
2,648 Posts
It's the "body boxes" that house the body mounts. They are right where the rear of the wheel well meets the firewall.

Why do you say the NY car isn't from road salt?
I misunderstood the location OP was referring to. The body boxes are at the outside corners of the floor pan, not the inside near the trans tunnel as pictured.
 

·
Premium Member
Joined
·
44 Posts
My issue was a missing drain hose elbow on the a/c drain.

A couple little plastic elbows are press fit and slid right over the drain from the condenser.
I added an extention since this pic was taken so it doesn't drip on the frame directly, and painted it black for effect.

Gas Motor vehicle Electrical wiring Auto part Cable
 

·
Registered
Joined
·
46 Posts
Discussion Starter · #18 ·
Was just about to come back to this thread to ask for specific pics of the area around the possible cause of the issue but I see some of y'all have already attached pics. Appreciated. Hopefully these remedies will sort out the problem.
 
1 - 20 of 20 Posts
Top