Firewall/Under Dash Water Leaks

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dodgedart1968

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My newly acquired '68 Dart has wet carpets and surface rust on the floor under the dashboard. I'm going to replace the windshield seal. Other than that source, what is the likely source of these leaks.
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Wiper pivot seals.
Rotted metal in the cowl plenum (around or near where the fresh air ducts attach to the underside of the cowl, behind the dash).
Usually the only time the windshield gasket leaks is if it's dry rotted, or rust in the windshield frame; and you'd normally see water on top of the dash then, too.
 
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What he said...
Plus any of the firewall seals to things like the steering column, brake master cylinder etc.

Water can splash up there or if you wash off the engine compartment it van get in that way.

Best thing to do is get it all dry, have some one with a garden hose work from the lowest point to the highest point with a light stream of water while you (with the front seats removed) lay on your back with a flashlight looking for signs of water.
 
As above. But I’ll add to check cowl drains to make sure they’re not clogged with leaves etc.
 
AH, also check your master cylinder for leaks. Brake fluid will strip the paint off anything and then the rust begins.
 
AH, also check your master cylinder for leaks. Brake fluid will strip the paint off anything and then the rust begins
My master leaked inside and the florboard was goo. Cleaned it up and added some paint , no rust though.
 
Get under there with a flashlight and have a friend pour the water to it. You will see it!
 
We need to define "pivot seals". There is a difference between where the wiper housing seals to the body and the actual seal to where the wiper pivots. The problem can be in the pivoting point as well as the wiper to body gasket.
 
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I had mine leak where fresh air enters from the cowl like these pictures show rust holes.

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What a wealth of information! I've participated on many car forums, but never on one as responsive and helpful as this one. You guys are the best!
I'll follow-up on all of the suggestions. I've worked on cars for years, but never thought of the cell phone camera inspection idea (duh!).
I did notice that the firewall under the steering wheel column support has a cascade of rust stains, and appears to be a major contributor. I don't see any other rust tracks on the firewall.
I do recall that my '73 Duster had a wiper pivot leak, almost from new, so I'll replace those seals.
I'll do my best to clear the plenum of debris. Any suggestions on how to do so, other than blowing compressed air down through the grill, and up from the drain holes?
 
Only drains are at ends near the vent collars, behind hood hinges. There will be a pic of the drain/opening in a thread here somewhere.
Edit... found 1,
drain hole ???1969 Barracuda
From there, water and debris free falls to behind the dog leg section of front fender. Bottom of fender is spaced away from the rocker with large washers at 2 body bolts to provide another drain/opening down there. That would clog and cause fenders to rust too.
 
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In reference to the images of the red car with the plenum top removed posted above: can the plenum be accessed through the underdash cabin vent boxes, through the round holes shown, to reach in and remove debris using your fingertips?

Does removal of the heater box allow access to plenum?
 
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Drivers side just remove the vent box, passenger side remove the whole heater box to get up there.

In 1977 my wife was driving one of our 70 Darts in cold rain in traffic. The damned pivot seal leaked onto her foot and when she looked down the car in front of her slammed on the brakes - Grille, bumper, radiator, valance, hood, plus the damage to the other car - (((sigh)))
 
Have you checked the windshield wiper pivot seals???

Those get old and shrink allowing water to get inside the car....
I did mine. Still leaked. Need to do the windshield. Looks like a pain in the ***, as I've read you have to have the clips in and the trim to make sure it's fitted right. And my trim is missing... think my Bro I got the car from lost it
 
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