The only issue with butyl rope is that it gets VERY sticky and can be very difficult to remove. This is the stuff I have been using. You can get it on Amazon or Ebay.
Firewall Leak.
- Thread starter kygaca
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I used the butyl rope and it looks so tacky! I think it solved the problem, but once it gets warmer I want to removed the box altogether and sand down/repaint the firewall (engine is already out). I found some rust holes in the firewall over by my windshield wiper motor (caused by gunked up leaves and such) and that definitely seems like the culprit over on that side.
I just used one of those. The firewall gasket is thicker in the kit than the one sold by itself. Not sure why but it seals really well. All the other pieces are very well made.
How far do you want to get into this project ?
You can put the new gasket on from the front of the box but you have to remove all the screws that hold the box to the firewall. You'll need to pull it out as far as you can get it away from the firewall. The other thing thats a little tricky is getting the gasket behind the 4 little tabs at each hole. Once you remove the top half of the box you'll see what they look like. It will slip over the box from the front though.
I wouldnt use the 3M strip caulk in place of the gasket. That works better sealing the top half of the case to the bottom. The box has grooves for the caulk. Again, you'll see how it looks when its apart. The AC box itself has a wider channel for the gasket to fit in. You would have to use a ton of caulk.
The other thing you'll have to do is pull out the inner fender on the right side.
FYI, I had to take to top cover off the box because I forgot to put the ground wire on the heater core. When I tried to remove the top the little tabs at the holes wound up tearing the gasket in two spots. Thats why I had to redo all this crap. Piece of advice. While its all apart break those tabs off on the top cover. Theres 4 at each hole. Once its together and the screws are in you dont really need them. The gasket slips behind the bottom piece and doesnt really move. You'll see what I mean when you do it. This way if you ever have to take the box apart again you wont have the same issue I did. You should also put a glob of strip caulk in each screw hole since it seals the hole up as the screws suck the gasket tight.
From putting a bunch of 78-88 A/G bodies together I found GM used the foam gasket and a seam sealer that did not stay pliable. On most cars the seam sealer cracked allowing water to accumulate on top which slowly rusts the firewall. One of my Malibu's required metal work and replacement of the firewall section.
I have found that the foam seal is usually in good shape. I successfully reused it on several cars including my Grand National. I would not eliminate the foam seal as it does also provide some cushioning and sealing. Most of the sealing was provided by the seam sealer. After struggling with a car that someone re seam sealed I decided I would use the strip caulk. I like it because it stays pliable and it's easily removed if you have to remove or replace items. GM used it on cars back in the 60's and many times it is still pliable 50+ years later.
On my current Malibu I did not remove the box. I just used the strip caulk and fixed the leak and it is a clean enough job to look factory.hth
I have found that the foam seal is usually in good shape. I successfully reused it on several cars including my Grand National. I would not eliminate the foam seal as it does also provide some cushioning and sealing. Most of the sealing was provided by the seam sealer. After struggling with a car that someone re seam sealed I decided I would use the strip caulk. I like it because it stays pliable and it's easily removed if you have to remove or replace items. GM used it on cars back in the 60's and many times it is still pliable 50+ years later.
On my current Malibu I did not remove the box. I just used the strip caulk and fixed the leak and it is a clean enough job to look factory.hth
The HVAC box is not the only source of leaks. The sheetmetal seams can also leak water, as engine heat cooks and dries out the seam sealer. Also there wre two holes, one in corner of the firewall that are poorly sealed by GM that are common sources for leaks. Resealing those holes requires pulling both front fenders.
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