New member, new truck, leak under dash
 

Good morning all. I am brand new to this forum and a brand new square body ('78 shortbed) owner. We had a real downpour yesterday and the floor under the dash quickly became wet, as in standing water. The water was dripping from a small (maybe 2.5"), circular hole above the brake pedal. The hole contains a disc, with directional louvers, that is rotatable to direct airflow. This hole appears to be in a heat/ AC duct. Any ideas as to how the water is getting there? Any help will be much appreciated.

Clockdoc

Re: New member, new truck, leak under dash
 

Wow....well, that is the lowest point of the AC ducting. For water to be getting in there, you must be getting water in through the main firewall opening a possibly through the heater hose area. The foam seal shrinks over time and the factory sealant gets dryrotted, water runs through the hood/cowl seal or past the foam hinge seal and directly flows on top of the heater hoses. Once water gets in, it can fill up the ductwork and leak in strange places. This is all assuming water is actually IN the ductwork and not coming from a leak higher above and simply dripping off it.

Re: New member, new truck, leak under dash
 

Thanks for the response. The water was definitely inside the duct. After removing the directional louvers, I reached inside with a finger and brought it out wet. Today, I removed the plastic fresh air intake grill on the cowl and inspected the inside of the cowl. The seam on the firewall side looked very suspect with a gap of about three inches in the center that looked to be completely open. This gap was at what appeared to be the lowest point, where water was most likely to pool. Additionally, there were a number of other points that looked bad, as well as evidence of previous attempts to apply sealant.

After blowing out loose debris, I wire-brushed and solvent-cleaned the length of the seam that I could reach and then dried it out with a heat gun. After the prep, I brushed in/on probably a 1/2 pint of seam sealer (pictures below). By that time, it was beginning to get dark (and cold) and I buttoned things up and quit. Plan to test tomorrow (or tonight if it rains again).

I'll post the results after I test.

Thanks again,
Clockdoc

Re: New member, new truck, leak under dash
 

I'm having the same problem but its on my passenger side and not nearly as bad as yours sounds. I had read in a few places to clean out the drain holes under that cowl but have not found any good pictures of where they are located exactly or found the time to pull mine off (was under the impression hood had to be removed). Thanks for posting those pictures up now I know where I should be looking for my problem. Good luck hope it works for you.

Re: New member, new truck, leak under dash
 

Water drains at each end of the cowl and it is difficult to see the openings. It rained here most of the night and there was no water in the floor this morning. Good luck with your problem.

Clockdoc

Re: New member, new truck, leak under dash
 

That cowl area is the number 1 spot on the drivers side where leaks occur. So your leak must be dripping ON your ducting and not in it-that factory seam is a terrible design. There is only a series of pinch welds where that portion of the firewall meet the floor and then there's the seam sealer inside the cowl....that's all that is keeping mother nature out.

For anybody restoring their interior, I'd suggest completely stripping and re-applying the cowl seam sealer and applying it inside on the seam as well. The side channels do route water away but guess what that water will rust out? There are sheet metal screws securing the cab windlace to either side....those holes will rot out from the regular supply of drain water rushing past....not to mention mud, dirt etc. So those holes should get a generous supply of buytl putty pressed in and on the screw threads as well-that will help seal up the holes. If you have a riv-nut gun you can get real tricky and secure some sealed 1/4-20 stainless nuts in place and secure the windlace with larger panhead type stainless machine screws....kinda overkill but it is a solution to them damn holes always rotting away...mainly due to the oem screws rusting first.

Re: New member, new truck, leak under dash
 

Thanks for the insight.

Re: New member, new truck, leak under dash
 

Looks like I was wrong. It must have just not rained hard enough last night. Testing with a hose today produces the leak pretty quickly when sprayed on the drivers side of the windshield. Water does come from inside the plastic duct. I can stick my finger into the duct and drag water to the hole from the inside. Water also drips from the dash next to the kick panel. Water directed on and around the heater box and heater hose connections under the hood doesn't seem to affect the leak. Water sprayed on the passenger side of the windshield doesn't seem to have an effect. water sprayed directly into the cowl opening doesn't produce the leak.

Do you have an illustration of all the ductwork behind the dash? A better understanding of what is where back there might be helpful. Thanks for your help.

Clockdoc

Re: New member, new truck, leak under dash
 

Maybe the windshield base is leaking into the defrost duct openings.....I can't think of anything else it could be.....

Re: New member, new truck, leak under dash
 

Everything does seem to point that way. I hadn't thought of that possibility. That would explain it being inside the duct. I'll try a bead of silicone all the way across the bottom and up each side 4-5 inches and drag out the hose again.

Thanks again for your input.

Clockdoc

Re: New member, new truck, leak under dash
 

I have the same problem and had no clue where to look, I'll be watching!

Re: New member, new truck, leak under dash
 

It's been too cold here to spend a lot of time on the truck but I did take the dash out so I could see better. Found one place in the perimeter of the windshield gasket where water had been coming in. This spot was near the lower left corner, as viewed from the inside. Still don't know where it is getting in.

Clockdoc

Re: New member, new truck, leak under dash
 

Just in case anyone has been waiting to see how my leak turned out, I thought I'd make one last post on the subject. Water was entering the cab from the lower, driver's side of the windshield rubber. It was also getting into the ductwork and dripping out of the lower air register. I never really defined the source of water entry but after doing the following, an afternoon of steady rain has not produced a puddle on the floor.

Bead of silicone on top of upper WS rubber (rubber to roof), bead of silicone on lower WS rubber (rubber to glass), bead of silicone on upper edges of blower motor and heater box and a new gaskt between the hood and the cowl. The silicone applied to the upper WS rubber was extended about halfway down each side.

Thanks to all who responded to my initial post.

CLOCKDOC