Cab leak mystery.

[Barbecue]

Hey, all.

I've had a leak in my cab as of late which seems to have somehow mysteriously fixed itself. Just wondering if if you guys wouldn't mind sharing your thoughts on my hypothesis or similar experiences.

Background: bodywork done approx 8 months ago which included removal of the windshield and new metal in windshield opening. Driver's door also removed during this process (wasn't hung very well). After returning home and washing my freshly painted truck, I noticed a fair amount of water on the driver's floor mat. I added additional butyl sealer around the windshield and under the driver's side drip rail (wasn't tight to the cab) but still the leak persisted. On rainy days it leaked a bit, but worst when washing. Fast forward until last month, still leaking a bit. Determined that leak was coming from inside the dash, up high, likely somewhere close to where the A-Pillar descends.

Now, we've had a fair amount of rain as of late, but the truck hasn't leaked at all. Washed the truck yesterday, making sure to dump very heavy amounts of water on the windshield, roof, and in the cowl while constantly checking inside for water - no resulting water inside the cab. It is as though the leak somehow has fixed itself!

My hypothesis is that somehow a drain hole somewhere may have been plugged with heavy dust and grit from the body work and the resultant lack of draining caused an overflow of a drain channel leading to the water presenting itself in the cab. Is it possible that this blockage could have cleared itself resulting in the "fix"? Thoughts?

Thanks in advance; I know this one is a bit out there...

[Matt Man]

If you don't have AC, it is leaking through the driver side kick panel? Mine leaks in the same place.

[motornut]

yup here, a couple of places to check,
road spray gets up behind the fender

[gmachinz]

I can almost guarantee your leak is coming from the seal inside the wiper cowl area. It gets dryrotted over time and mud/debris can act as a plug at times but will eventually wash back out.

[chengny]

Here is the RH side fresh air plenum - there is a similar setup over by the parking brake for the driver.

On trucks not equipped with AC there are flaps in the kick panels on both sides that can be opened to allow fresh air into the cabin (AC equipped trucks have no provision for this on the LH side). This happens without the use of the blower (or passing through the heater core - blend doors tend to leak and allow some heated air to pass). It just flows into the truck as a function of road speed.

The plenums start at either end of the intake/wiper cowling that runs across the truck - in front of and under the windshield. They run down past the flaps and terminate at about the level where the door bottom is.

There is, by design, an opening at the very floor of the trunk to allow any entrained rain, car wash, melted snow that comes in with the fresh air to drain and fall to the ground.

If these get plugged up with rust, leaves, dead mice, etc - the water will rise and eventually spill out of the vent flaps. Poke them out from inside the vestibules with a coat hanger or something similar - or blow up from the bottom with compressed air.

[Barbecue]

Originally Posted by gmachinz

I can almost guarantee your leak is coming from the seal inside the wiper cowl area. It gets dryrotted over time and mud/debris can act as a plug at times but will eventually wash back out.

Thank you so much for the feedback, everyone. Such a wonderful resource we have here and I appreciate everyone's consideration.

Regarding the fresh air vents, my truck is an AC-equipped one, so I'm afraid that won't be the fix.

gmachinz, thank you for the suggestion. I haven't removed the cowl grille as of yet (should do so asap), but can I assume that the seal you're referring to is where the floor of the cowl seals to the cab (the back portion)? This definitely sounds like it could be right as the leak is coming from quite high up...

[gmachinz]

Yep...just look in the wiper linkage area and you'll see what I'm talking about. My Shortbox had a leak from somewhere up high in the dash on the drivers side and water only collected in the damn middle of my floormat. It took me awhile to find the leak myself. I only found it myself after deciding to grease my wiper linkage for the helluvit. The seal had a bunch of moist mud/dirt/leaves, etc. and I figure what the heck.....I power washed it clean, dug out the loose sealant and resealed it with 3M seam sealer then undercoated it-never leaked again.

[Barbecue]

Originally Posted by gmachinz

Yep...just look in the wiper linkage area and you'll see what I'm talking about. My Shortbox had a leak from somewhere up high in the dash on the drivers side and water only collected in the damn middle of my floormat. It took me awhile to find the leak myself. I only found it myself after deciding to grease my wiper linkage for the helluvit. The seal had a bunch of moist mud/dirt/leaves, etc. and I figure what the heck.....I power washed it clean, dug out the loose sealant and resealed it with 3M seam sealer then undercoated it-never leaked again.

Excellent advice, thank you so much! You gents have rejuvenated my enthusiasm for addressing this issue - building exhaust systems and dressing up wheels is so much more fun than fixing leaks haha.

[gmachinz]

No problem. I think that area over time has an issue keeping rain out if its a slow, drawn out rain or drizzle for several hours or days. Short, heavy downpours and it wouldnt leak. The water is supposed to drain out of that area along the side and then bottom of the cowl (which is also why the windlace seal retaining screw holes get rusted out-great design there GM!) but a steady rain causes that dried out seal to take in water and creates "drips" inside the cab.

[Barbecue]

Stupid question. Really stupid question. How do I remove the wiper arms? I feel like an idiot!

[tucsonjwt]

There is a clip on the wiper arm which presses against the knurled gear end of the wiper drive. You need to release that clip, then you can pull the arm up and off. It is best to go to the local auto parts store and buy a wiper arm removal tool for GM. Or you can probably get one cheaper on Ebay or Amazon.

http://www.autozone.com/test-scan-an...ol/439291_0_0/

You put the hook under the arm and pull the tool toward the arm - that hook releases the clip and you can pull the arm off. You can use a flat blade screwdriver to release the clip but I always scratch up the cowl vent when I do that.

[tucsonjwt]

Other methods:

https://www.youtube.com/watch?v=Pzu09eJ6vpo


https://www.youtube.com/watch?v=hv9pummW0oc