Water ingress: factory defect on early c4 convertibles
12-10-2013, 06:20 PM
#1
Water ingress: factory defect on early c4 convertibles
I have been chasing the origin of a water ingress on my 1986 convertible for years, actually since i bought it back in 1999 in sunny California. I did not noticed it that much in the beginning due to california climate and car sitting in doors. Now that I have been in the french riviera for more that 10 years with the car sitting outdoor and ever stronger rains at fall and spring seasons, I often found the car in the morning with a full buck of water on the passenger and/or driver foot well, depending on how I was parking the car (at least I thought).
What was distrubing is that it was never the same. After an heavy rain, sometime the car was all dry, sometime slightly wet, sometime full of water, sometime driver side, sometime passenger side or both.
Of course I have replaced all the weatherstrips (doors, windshield and convertible top. I have tried to glue them all. I even disassembled the windshield weatherstips rails on top and each side and re-assembled them with exterior sealing tape as original. I added silicon sealing in between the rails and between inner rail and windshield. I greased the weatherstrips with silicon grease. Nothing worked. Still water ingress. Maybe even more than before. Every now and then, I have one occurence of significant rain without ingress, letting me think I eventually fix it. But too bad, the next time the water is back again.
I was at the point where I thought I had completely fixed it and started to change my carpets with a brand new set (see my other post), but in the middle of the restoration, I found the car once again full of water after a heavy night rain.
I was out of ideas and continued my carpet replacement a little desperate. This is when I noticed a very strange thing while I was cutting the rear wheel well carpet panel. I had the portable lamp inside the trunk and was working around the convertible lid latches when I could see the light through this water evacuation hole!!
I assume GM engineers wanted this hole to end up in the space between the outside body panel and the trunk inside wall, but the space is so narrow in that section of the body that a good half of the hole ends directly in the trunk. I might have aggravated things over time since I remember I tried to enlarge this hole that seemed to be partially obturated and always full of debris. Now I understand several things:
- the hole is partially obturated because it falls just above the wall separating the trunk from the wheel well. What looks like some epoxy glue was right in the middle. This glue was likely used to join the vertical trunk wall with the body outside panel.
- depending on how well I was cleaning the hole, or at some times letting it full of debris, I could have more or less water entering in the car. Once the carpet was removed, I could see the dirt showing how the water was leaking under the carpet mass back behind and below the seats, down to the foot well.
- no wonder why I could not see any vertical leaking pattern in my foot well walls, water was not coming from the front but from the trunk, behind the seats.
I decided that it was too narrow and risky to try to redirect this tiny hole to where it should originaly go, especially on one side where 2/3 of the hole ends up just above the trunk side rather than the wheel well side. Si I preferred to force the water to go through the trunk, behind the carpet, through a large enough tube (so that it does not get clogged with debris like before) and get the tube to go through the trunk bottom wall, to the wheel well. I glued the tube at the top and the bottom with silicon seal. I tested the tube sealing by dropping large amount of water in rail around the convertible lid opening and looking at the water going safely through the tube, to the wheel well.
Here is where the tube goes through the trunk bottom wall to the wheel well, at the vertical of the convertible lid latch area.
What was distrubing is that it was never the same. After an heavy rain, sometime the car was all dry, sometime slightly wet, sometime full of water, sometime driver side, sometime passenger side or both.
Of course I have replaced all the weatherstrips (doors, windshield and convertible top. I have tried to glue them all. I even disassembled the windshield weatherstips rails on top and each side and re-assembled them with exterior sealing tape as original. I added silicon sealing in between the rails and between inner rail and windshield. I greased the weatherstrips with silicon grease. Nothing worked. Still water ingress. Maybe even more than before. Every now and then, I have one occurence of significant rain without ingress, letting me think I eventually fix it. But too bad, the next time the water is back again.
I was at the point where I thought I had completely fixed it and started to change my carpets with a brand new set (see my other post), but in the middle of the restoration, I found the car once again full of water after a heavy night rain.
I was out of ideas and continued my carpet replacement a little desperate. This is when I noticed a very strange thing while I was cutting the rear wheel well carpet panel. I had the portable lamp inside the trunk and was working around the convertible lid latches when I could see the light through this water evacuation hole!!
I assume GM engineers wanted this hole to end up in the space between the outside body panel and the trunk inside wall, but the space is so narrow in that section of the body that a good half of the hole ends directly in the trunk. I might have aggravated things over time since I remember I tried to enlarge this hole that seemed to be partially obturated and always full of debris. Now I understand several things:
- the hole is partially obturated because it falls just above the wall separating the trunk from the wheel well. What looks like some epoxy glue was right in the middle. This glue was likely used to join the vertical trunk wall with the body outside panel.
- depending on how well I was cleaning the hole, or at some times letting it full of debris, I could have more or less water entering in the car. Once the carpet was removed, I could see the dirt showing how the water was leaking under the carpet mass back behind and below the seats, down to the foot well.
- no wonder why I could not see any vertical leaking pattern in my foot well walls, water was not coming from the front but from the trunk, behind the seats.
I decided that it was too narrow and risky to try to redirect this tiny hole to where it should originaly go, especially on one side where 2/3 of the hole ends up just above the trunk side rather than the wheel well side. Si I preferred to force the water to go through the trunk, behind the carpet, through a large enough tube (so that it does not get clogged with debris like before) and get the tube to go through the trunk bottom wall, to the wheel well. I glued the tube at the top and the bottom with silicon seal. I tested the tube sealing by dropping large amount of water in rail around the convertible lid opening and looking at the water going safely through the tube, to the wheel well.
Here is where the tube goes through the trunk bottom wall to the wheel well, at the vertical of the convertible lid latch area.
12-10-2013, 08:21 PM
#3
A Corvette with a leak ????????? 
Say it ain;t so !
They're supposed to leak. That gives the thousands of Corvette owners something to do when it rains when they can't go anywhere...
Say it ain;t so !
They're supposed to leak. That gives the thousands of Corvette owners something to do when it rains when they can't go anywhere...
12-10-2013, 10:48 PM
#4
Instructor
Member Since: Aug 2012
Location: Carrollton TX
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I think you may have just discovered where my passenger side leak is coming from, thanks!
I couldn't find where that durn leak in the passenger foot welll was coming from, so I'm going to pull that rear panel area apart and see if that's my problem, too. Appreciate the photos, that certainly helps!
I couldn't find where that durn leak in the passenger foot welll was coming from, so I'm going to pull that rear panel area apart and see if that's my problem, too. Appreciate the photos, that certainly helps!
12-11-2013, 12:41 AM
#5
Drifting
Just as a quick fwiw - you guys I'm sure have also made sure the front cowl vent drains are clean. There are rubber teats on each side - one near the battery, another on the other side at the bottom of the HVAC box (access by taking the lower body panel off) and one behind the windshield wiper motor. Often the rubber teats become clogged and the passenger floorboard is soaked as it is the lowest point of the HVAC system.