Drain Holes on Dash Inside Windshield

[DJ_Baar]

I remember prior Owner telling me he put silicon in leaks under dash - I found the three (3) factory holes he filled when restoring my '67 Chevy C20. See picture, this is one I found on passenger side. There is same on driver side and in middle of dash at windshield had covered by windshield seal.

* Can some one explain the WHY and won't any moisture just go into wiring and things under dash?

R/
DJ

[toolboxchev]

It does (rain). I am fighting a cowl leak and bad seal? The cowl area I have patched twice now with buytl rubber and it's still leaking in.

[DJ_Baar]

Trust me, we get some rain here along the Gulf Coast
I had annoying water leak onto dash and under dash and replacing wiring now due to corrosion --- trying to find and fix anything that may be leaking. Going to replace wiper motor seal and try to better seal cowl area --- thought I had.

[HO455]

Basically someone at GM made a decision based on what they thought was a good idea. It may have been to drain the soapy water off the dash after the glass was installed, or to let condensation that drips off the glass have some place to go. It's one of those things we will never know.

[DJ_Baar]

Thank you HO455.

So no reason I don't plug these drain holes?

If I have water on the dash, I want to know about it and not just go into and under the dash and wiring.

R/
DJ

[El Dorado Jim]

sub'd

[DJ_Baar]

Originally Posted by El Dorado Jim

sub'd

???

[Grumpy old man]

Don't plug or seal the dash weep/drain holes , they are there for excess condensation in a 50 year old truck , if you have water leaking into your cab it's coming from outside from a leaking cowl or bad windshield gasket , time for you to crawl in upside down with a flash light while someone helps by pouring water into your cowl vent so you can find the leak , those little dash vents have nothing to do with water leaking into your truck , time to pull your exterior cowl panel off and start looking for the leak , also clean all the leaves and debris out and check the lower vent drain scuppers to make sure they are not plugged and draining correctly
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[special-K]

I agree with Grumpy. What you are worried about is water from outside, not a "possible" drip every once in a blue moon from condensation. The problem is elsewhere. I recommend going under the dash "w/o" a flashlight to look and having a friend "with" a flashlight shine it so the light will come through any breeches. If you don't catch light peeping through it isn't a direct path and it's time for the light under/water up top system

[DJ_Baar]

Thank you both (Grumpy Old Man & special-K)!

I am completely going thru cab now replacing anything rusted beyond repair with patch panels to include the drip rails over doors. Passenger side must have been left exposed because most damage there. Cowl looked OK, and will take another look at that, seal it good and replace windshield wiper seal too. Then check for leaks as you both explained - again.

I came across those weep holes and knew there had to be a good reason. Thanks again for sharing the wealth of information experience brings.

R/
DJ

[LongBox]

Agree that water in the cab is annoying, and that the cowl area of our old trucks was not well designed in terms of preventing rust. I've had my outer cowl panel off, and thoroughly cleaned that area. I am concerned about leaves and other debris in the kick panel vent areas of these trucks. I can reach in, and find old leaves. Is there supposed to be a water drain in the bottom of those vent areas?

[DJ_Baar]

That's a good question Rick. I have access and can add vent holes there now, but note that is not an area I have rust to fix on this '67 Long Bed C20.

DJ

[Grumpy old man]

Originally Posted by LongBox

Agree that water in the cab is annoying, and that the cowl area of our old trucks was not well designed in terms of preventing rust. I've had my outer cowl panel off, and thoroughly cleaned that area. I am concerned about leaves and other debris in the kick panel vent areas of these trucks. I can reach in, and find old leaves. Is there supposed to be a water drain in the bottom of those vent areas?

Remove the kick panel vent it's spring loaded so it will move out of the way easy enough , reach in and start pulling all the old leaves , mice skeletons , and god knows what , get you shop vac in there and clean it out in the bottom towards the back you'll feel the drain
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[DJ_Baar]

I done that but GREAT advice to LongBox. I thoroughly cleaned and painting with quality rust converter to keep problem at bay.

[davepl]

I don't know if Grump is right - I assume he is - but my take on it is this:

GM didn't do anything that cost any money if it didn't have to be done. If it cost them 50 cents to drill those holes on a truck, that's half a million dollars some dude in jazzy suit didn't save them. That's a fat bonus in 1967 dollars! If only it worked that way...

But suffice to say GM didn't do a lot of unnecessary steps, and if they did, they often economized them out of the process by the end of a model run.

So, if you see it on all 5 years of our trucks, it's probably required.

If you see it in the 67s but not the 72s, it's probably a good idea.

If you see it in the 72s and not the 67s, it's something they had to add during production and is therefore probably a very good idea.

Those are just my general guidelines. I assume these holes are there for a reason (condensation most likely).

---

To Longbox: wear gloves!

[3drburb]

Originally Posted by davepl

I don't know if Grump is right - I assume he is - but my take on it is this:

GM didn't do anything that cost any money if it didn't have to be done. If it cost them 50 cents to drill those holes on a truck, that's half a million dollars some dude in jazzy suit didn't save them. That's a fat bonus in 1967 dollars! If only it worked that way...

But suffice to say GM didn't do a lot of unnecessary steps, and if they did, they often economized them out of the process by the end of a model run.

So, if you see it on all 5 years of our trucks, it's probably required.

If you see it in the 67s but not the 72s, it's probably a good idea.

If you see it in the 72s and not the 67s, it's something they had to add during production and is therefore probably a very good idea.

Those are just my general guidelines. I assume these holes are there for a reason (condensation most likely).

---

To Longbox: wear gloves!

I found these on my 78 GMC and wondered the same thing.

[Grumpy old man]

Originally Posted by davepl

I don't know if Grump is right - I assume he is - but my take on it is this:

GM didn't do anything that cost any money if it didn't have to be done. If it cost them 50 cents to drill those holes on a truck, that's half a million dollars some dude in jazzy suit didn't save them. That's a fat bonus in 1967 dollars! If only it worked that way...

But suffice to say GM didn't do a lot of unnecessary steps, and if they did, they often economized them out of the process by the end of a model run.

So, if you see it on all 5 years of our trucks, it's probably required.

If you see it in the 67s but not the 72s, it's probably a good idea.

If you see it in the 72s and not the 67s, it's something they had to add during production and is therefore probably a very good idea.

Those are just my general guidelines. I assume these holes are there for a reason (condensation most likely).

---

To Longbox: wear gloves!

Take a drinking straw place it on your bench and smack it with a hammer , the end result is the approximate size of the dash drain vents , now using your best flashlight look at the crease where your winshield gasket meets your dash directly in front of the light switch on the left side of your dash , also directly in the middle again where the windshield gasket meets the dash in front of the speaker mesh , there are 3 vent drains across the dash . Back in the day when we used to destroy the K-20's hauling firewood the occasional cup of coffee would spill onto the dash and leak right onto your boots , you can clear the vent drains using a toothpick when sawdust used to fill the holes , haha
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[lutronjim]

I glued window screen under the slots of my cowl cover. I had truck painted which painted window screen - you can hardly tell its there. Keeps a huge amount of leaves and pine straw out.