There was a series of posts in the past few months regarding midyears leaking from somewhere around the fresh air plenum. I think my 67 coupe is leaking in this area, but I can't find the string in the archives and I don't remember the particulars. Can someone help me out?
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Re: Midyear water leaks
I would like to hear more on this, my '67 is prone to this. -
Re: Midyear water leaks
On a 66 with air the plenum is a poor design and has no way to pull the unit up against the gasket except one small stud. Don't see how any of them didn't leak. I assume non air cars are similiar.Comment
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Re: Midyear water leaks
I'm not sure you have the same problem, but I had water leaking in thru my fresh air vent whenever I washed the car ('66). I was ready to start removing parts to find the problem until someone on this board told me something to check first. He said the drains from the top vent grill over time get clogged with debris causing water to back up into the fresh air vents. He said to find the quarter sized outlet on the frame just behind the front tires and shoot compressed air from below (after removing the vent grills). I was in the process of replacing my carpet and had already removed it and since I don't have a compressor, I used my garden hose with a pressure nozzle (moderate pressure, not full blast). I alternated pointing the hose down into the grill vent and up from the outlet and you would not believe how much crud came out! There was dirt, decaying leaves, twigs and who knows what else. It took about 10 minutes per side to get the water flowing clear and free and I haven't had a problem since. I'm not sure your problem is related, but the plenum may get fresh air from the same source and the water leak could be caused by a drain blocked. It's easy to clean out and worth a try. If you want to use the garden hose, but not get your carpet wet, you could put several towels up against the fresh air vents to catch anything before it hits the carpet.Comment
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Re: Midyear water leaks
Clearing that drain was part of the discussion, but there was reference to a seam somewhere in that area that has a propensity to spread and cause a leak in the area of the vents. Mine does it on both sides, maybe a little worse on the driver's side. I'm wondering if the dash has to be removed to access the area. I can't see anything from underneath. I don't think it's coming from anywhere around the windshield, but no way to really tell for sure without removing the whole dash. That's a pretty good task. I've done it before,to do a [gasp] interior color change. However, if this seam can be accessed otherwise I'd rather put off the dash removal for a while.Comment
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What I've seen
By 1970, most mid-year Corvettes I encountered were leaking in the windshield area. I know of very, very few that don't leak somewhere these days.
The leaks up front that I have seen were caused by the following:
1) rusty windshield channel
2) separated upper body panel seam at firewall/cowl vent
3) improperly installed windshield weatherstrip and trim (usually missing bedding compound)
4) misaligned a.c. duct box seal at passenger side kick panel
5) clogged cowl vent drain
6) improperly repaired collision damage
7) leaking weatherstrips in front door jambs
no "vapor" barrier behind door panels or missing calk seal (I don't know why this goofyass smiley face is showing up instead of the number eight)
9) clogged drain holes in bottom of doors
10)poor seal at front of soft top
Ed, the firewall body seam that usually separates is accessable with the cowl vent grills removed. Often it can be re-sealed by applying bedding compound around the edges of the cowl vent opening floor.Comment
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Re: What I've seen
Thanks, Jerry. I think I may have a combo of #2 and #7. I have new w/s on the doors, but the "aux w/s" that is held on by the little push clips doesn't look to me like it seals very well. Should it be glued or otherwise sealed to the door? I'll pull the cowel vents and look there and see if I can see any separation.Comment
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Re: What I've seen
Hey, Jerry! I think I found the leak. There is a seam at the front of the plenum right in front of the wiper transmission that appears to have cracking in the sealer all the way along the seam. i'm not familiar with "bedding compound"> What id it? Is there anything I can get at the harware store that would work? My old standby, rope caulk, won't stick.
Also, I think I'm looking at the back side of the vent. Is there a seal where the vent assy attaches to the body? Looks like it could leak there also.
Last question. Where is the drain? Looking down into the plenum, I don't see one.As always, thanks for the advice.Comment
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Re: What I've seen
I would think that silicone sealer (sold in tubes at the car parts stores) or even high quality silicone bathtub caulk could be used to seal it up. Brush-on automotive seam sealer (normally used for sheetmetal seams, but would likely work on fiberglass) is sold by mail-order suppliers like Eastwood, and is probably also available at your local body-shop supplies store.Comment
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Bedding compound vs. strip calk vs. silicone
I use 3M Automotive Bedding and Glazing Compound #08509. It is black and comes in 10 oz. tipped tubes you squirt using a calk gun. It has the consistency of very thick toothpaste and pretty much stays that way. Over time it eventually gets about as hard as road tar. It is sold at both auto parts and paint stores. Most show car folks hate it because it's messy and continues to ooze out for years. I use it to seal windshield weatherstrips and trim.
I also use 3M Automotive Strip Calk #08578. It is black and comes in 1 ft. strips. There are 20 yds. in each box. It is much stiffer than bedding compound. In fact, it gets real stiff with cold temps and age. It has much better adhesion than hardware store rope calk. I use it to seal door hand-hole covers and vapor barriers. I've only found it at good auto paint supply stores.
I've also used a 3M product called Windoweld. It is black and comes in coiled rolls about 15 feet long. It is made to attach modern (post '67) windshield glass to the body channel. It has a real death grip on smooth, clean surfaces. It stays sticky until the skin gets dirty. There are two thicknesses offered. Both are roughly 3/8" in diameter. It is sold at auto glass and paint stores.
All the above products stay somewhat sticky forever. Silicone hardens too much to suit me as a sealer. It isn't sticky to the touch after curing. It might remain attached forever, but if it breaks free it can't re-attach itself to anything.Comment
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Cowl vent seals and drains
If your car has factory air, there is a pitiful foam seal between the body and the a.c. duct box behind the kick panel grill. If you don't have a.c., there is no separate foam seal there - just a housing for the vent door.
Water is supposed to flow into the cowl vent grill, across the floor of the cowl opening toward the side of the car, and then down around the kick panel opening to a drain hole in the bottom of the body.Comment
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Re: Cowl vent seals and drains
Great infprmation. Thanks, again.Comment
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