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Circa 1996 Cab R Side Bulkhead Seal

299 Views 7 Replies 4 Participants Last post by  manbearpig
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Do you have any suggestions for sealing the bulkhead “connector” below the Cowl Drain Outlet on the R side for circa 1996 vehicles? I will call it a “connector” for simplicity. It is a very high water flow area, unfortunately. If I understand correctly, this connector was relocated to the firewall in one of the subsequent years, if not the very next model year. Probably a wise engineering decision.

I will explain factory installation as I understand it. The 2 – halves of the connector are split by a vertical seam into a left and right side. They apparently snap together, and were filled with a clear rubbery compound where the wires pass through. The top and bottom of the connector seam around the screw holes do not appear well to be sealed by any compound. The connector attaches to the cab with 2 – sheet metal screws. An ~¼” thick seal is sandwiched between the cab and connector. I appears to be sponge (foam) neoprene or similar. There was an additional, small piece of thin, butyl tape/ribbon applied to the cab over the top sheet metal screw hole. The top of the connector bedded in that. The top sheet metal screw also holds the plastic water deflector in place. The deflector is in no way sealed to anything; is a bit flimsy; but is well contoured to the body of the connector. Water entering into the top of the deflector will make contact with the side of the connector & neoprene seal. I actually am not certain what purpose it serves. Not shown is a weighted, rubber flap that covers the Cowl Drain Outlet; maybe to discourage vermin from entering.

The ¼” seal is compressed a bit, but not in terrible condition. What would you suggest for sealing this pass-through to the cab interior? I can source some butyl sealant to replace the small ribbon/tape I previously removed; screw the connector (w/ original seal) and deflector back in place; and replicate the original, factory solution. However, I do not want to remove all the front end sheet metal again to correct water intrusion to the Cab interior.

Thank you in advance for you suggestions.
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Maybe my post is unclear. I do not understand your suggestion. What specifically do you suggest I remove?
Long-term presence of moist debris in the Cowl Plenum behind the R Drain Outlet caused seam sealer failure and rust; allowing a pathway for water from the Cowl Plenum into the Cab interior. I have repaired that. All front end sheet metal was removed in support of that investigation and repair, and remains removed. I am not confident in the factory sealing solution for the “connector” passing into the Cab below the R Drain Outlet. I am asking for opinions on sealing that connector, whether it be simply returning to the factory condition or pursuing a different solution. I will reassemble the front end sheet metal after I have considered suggestions and implemented an appropriate solution. I have some ideas, but do not want to bias potential responders.
So, in very general terms, both you and GM attempted/suggest a similar solution where the “connector” was/is sealed to the cab, but backed up by flashing/deflector. Depending on execution, the flashing you describe would potentially be a better implementation of the second part of that solution GM attempted with the black, plastic deflector.

There is no silicone on the mating surface of the “connector”. The seal is ¼” thick, neoprene sponge (foam) sheet, or something similar, with adhesive backing on the “connector side only. Are you suggesting adding silicone between the existing, or replacement, neoprene seal and the cab?
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