water leak into cab through floor vent over brake pedal

[gmbellew]

I have a suddenly new leak into the cab of the 1990 suburban. I washed the truck recently to knock off the road salt. after, I noticed some water on the driver floor. I just assumed that my 7yr old son directed some high pressure water into the door/body gap and it blew past the seal when he was "helping." but we have had some rain since then and I am getting water.

I went out during some rain today to investigate. The water is dripping out of the floor vent above the brake pedal. There MAY also be a small amount of water coming down the driver side kick panel way up above the ground bus bar. But that may have dripped in when I had the door open investigating.

My plan is to take that duct piece out and hose some water all around to try and locate the source. But I probably won't have time until this weekend to do that. In the meantime I have a small bucket to collect the leaking water, as there is rain in the forecast for the next several days.

It is such an unusual leak location that I thought maybe somebody has had a similar experience I could lean on to help pinpoint the water entry location.

 

[da_raabi]

So the water is coming in through the HVAC? I'm having a hard time picturing what you are describing.

 

[gmbellew]

i don't know where it is coming in, I suspect the windshield gasket. but most of the water was dripping out of the little floor vent (right above the brake pedal) that comes off the duct piece that runs under the dash from the main box to the lower left dash vent. there may also be some coming down the driver kick plate.

I have no idea how water was getting in that vent. I suspect it is coming down the driver side A pillar and coming in somewhere into the dash that it was getting into that lower left hand vent and coming out the little vent above the brake pedal.

 

[gmbellew]

The cowl drains seemed to be open and free flowing. There was tons of water flowing out with full hose spray into the cowl. Although I did seem to overwhelm the drain with full hose flow directly into the driverside drain. But I don't think it was designed to have that much water flowing to a single side...

I did notice that the top, driverside windshield gasket was pulled back from the cab to where there is an opening there. I can only surmise that water was flowing in there and overwhelmed the drain hole at the bottom of the windshield channel, and got into the cab that way. I didnt want to water test it, because then there would be water in there and I'd have to wait for it to dry out before sealing it. So I pulled the gasket back and squirted some weatherstripping adhesive in the gap and also "caulked" the gasket-cab seam on the corner with the adhesive. I had planned on using a flowable silicone, but read some information about that not being good on paint. It should get a few days to cure before any rain is in the forecast...fingers crossed things stay dry on the inside.

 

[shinkle]

I recently chased down 3 small similar leaks. I'm not sure this will help but one thing I learned was to slooowwly add water to one location at a time to eliminate entry spots. I focused on the cowl by putting a water hose at the cowl screen with slow water coming out of the hose and avoided the windshield. Let it run for a good while while watching under the dash. I did driver side first, then passenger side. Even though the cowl drains fast, doesn't mean they are clear.

My driver side and passenger side had small hairline cracks in the factory seam seal where the floor pan meets the kick panel. My cowl drained fast and clear but water would seep through the hairline crack. The carpet padding underneath was damp. Dug out all the loose seam seal, sanded, primed, sealed with automotive seam seal, painted. I eventually found mud and rocks up in the cowl drive under the driver door and picked it out with a screwdriver. Even though they drained fast they were partially blocked.

My second leak, still not fixed, is from the cowl factory seam seal cracking. Water is dripping in from the bottom of my steering column plate. To see this you have to remove the cowl vent screen and look at the seam down inside. Mine was so small I didn't see it the first time I removed the cowl screen.

Also, don't use any old caulk. At least use automotive seam seal, autozone has decent 3M.

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[gmbellew]

I did decide to remove the plastic access panels at the base of the fender at the drain outlet to see how the drain outlet looked. I started poking around and I couldn't believe the amount of stuff I got out, particularly on the driverside. I would get all I could with a thin rod, run some water to flush more down, and keep repeating. It took me over an hour before I couldn't flush out more stuff. It was a wet and dirty job, but worth doing after 32 years.

Hopefully between sealing the top corner of the windshield gasket and cleaning the drains, the cab will stay dry for another 32 years.

 

[da_raabi]

Something else to pay attention to; https://www.gmsquarebody.com/threads/apb-check-your-cowl-seam-seals.29801/

The seam at the bottom of the cowl likes to break up and rust, allowing water down between the two layers of steel that form the firewall. The result is water can come in through any bolt holes in the firewall, then allowing that water to end up in strange places. Might want to poke a camera or flashlight down in the cowl and look at the condition of that seam.

Mine was an absolute mess. In the thread above you can see everything I did to fix it. No more water now!

 

[Grit dog]

The seam at the bottom of the cowl likes to break up and rust, allowing water down between the two layers of steel that form the firewall. The result is water can come in through any bolt holes in the firewall, then allowing that water to end up in strange places.

100% true statement. My "clean" '86, no visible rust anywhere, had 2 water issues.
First one being the worst was water trapped under the windshield and back window gaskets. Ate through the Sheetmetal from the outside. Good part was after cutting out some bad spots, I confirmed that the rust was worse on the outside, so basically whatever was rusted through was the extent of it. I'd recommend anyone who is keeping their truck nice, remove the front and back windows and fix any surface rust. It will be mostly or all hidden, so much easier to fix/seal and reinstall window gaskets.
The other was water leaking through the cowl seam. Not alot, nothing rusted out or even close, but began pitting the floorboard sheetmetal. And I could tell that the carpet insulation had been wet in places that weren't heater core or wet boots related.
I tried sprayable bedliner in the cowl seam, loaded it in, thinking it would do a flex seal thing. Once it cured, it shrunk and cracked. So I topped it with seam sealer and it hasn't cracked.

 

[1lejohn]

There is also a grommet that enters the engine compartment above and to the left of the pedal. Mine is dry rotted and let water into the cab. it's below the duct can't see the water running up and off the duct.

 

[gmbellew]

I did decide to remove the plastic access panels at the base of the fender at the drain outlet to see how the drain outlet looked. I started poking around and I couldn't believe the amount of stuff I got out, particularly on the driverside. I would get all I could with a thin rod, run some water to flush more down, and keep repeating. It took me over an hour before I couldn't flush out more stuff. It was a wet and dirty job, but worth doing after 32 years.

Hopefully between sealing the top corner of the windshield gasket and cleaning the drains, the cab will stay dry for another 32 years.

update- we had about an inch of rain last night, some of it very heavy. the cab stayed dry, so I am hoping that we have resolution!