[9c1_9c6_fan]

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?

 

[Caddylack]

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?

 

[Lance]

Water from the AC evap drain. Soaks the entire area. Never know because it's covered by a floor mat usually.

 

[96 Black]

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".

 

[1Slammed96SS]

How do we come about fixing this issue? Cuz I would like to know to prevent this as well?

 

[1Slammed96SS]

Hey 9c1_9c6_fan is this on the inside of the floor board or the outside? It’s hard to tell from the pic.

 

[9c1_9c6_fan]

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.

 

[9c1_9c6_fan]

Hey 9c1_9c6_fan is this on the inside of the floor board or the outside? It’s hard to tell from the pic.

It's on the inside. I lifted the carpet and insulation out. I'll take a better pic of the area now.

 

[1Slammed96SS]

I see that, now I’m anxious to see mine.

Thanks

 

[95wagon]

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

 

[96 Black]

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:

RESOLVED: AC drip pan water leaking onto passenger floor

I'm re posting this with all the info I've written on this problem so it will be in one place and hopefully easily found by anyone with the same issue. This has been a long, frustrating process, but I believe I have finally licked this problem! It's a cautionary tale for all B-body owners...

www.impalassforum.com

And there's even word the cowl can leak - but about 1/2% rare.

 

[95wagon]

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.

 

[Fred Kiehl]

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.

 

[buickman1]

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.

 

[Caddylack]

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.

 

[95wagon]

 

[jetfire88]

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.

 

[9c1_9c6_fan]

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.

 

[95wagon]

not great photos but this is my added drain tube

 

[ottmywyFS]

Water from the AC evap drain. Soaks the entire area. Never know because it's covered by a floor mat usually.

this is correct the insolation between the A/C heater box goes bad or disapears condensation builds on the A/C line and drops down onto the follr pan