GM B-Body Forum, 77-79 Caprice/Impala Forum

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GM B-Body Forum, 77-79 Caprice/Impala Forum

A forum for the owners and enthusiasts of General Motors B-Bodies from 1977-1990, but dedicated to the owners of 1977-1979 Impalas and Caprices. Join up now!


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HeavyChevy77
Sean Donica
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    Wet floorboard

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    Post  Sean Donica Sun Jul 16, 2017 9:44 pm

    I'm redoing the interior on my 77 Impala, and when I took up the carpet and jute backing at the front passenger side, I noticed the floorboard was wet from about the front of the door to the firewall. The car had not been driven in at least a week, but had been driven in the rain at that time. Any ideas where the leak could be coming from? Nothing seems to stick out. Thanks!
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    Post  HeavyChevy77 Sun Jul 16, 2017 10:43 pm

    Heater core probably
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    Post  Sean Donica Sun Jul 16, 2017 10:47 pm

    I was searching the forum and guessed as much. How do I stop the leak?
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    Post  HeavyChevy77 Mon Jul 17, 2017 1:43 am

    There's a cheap way and a free way
    Cheap way
    About 30 rockauto
    And some time a few hours time to remove rh wheel and hvac housing box remove core re seal and assembly and bleed coolant
    One of the members did a complete write up in how to I think it was myloth

    Free way
    By pass heater core
    Hose from top of water pump to front intake manifold water inlet on the front right (pass)corner

    I did the freeway been like that a few years now that I did my motor swap time to alot of hvac and elec work
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    Post  Kit1078 Mon Jul 17, 2017 8:02 am

    The HVAC box is also known to leak where it meets the firewall. I've also seen where the drain on the bottom of the HVAC box gets plugged and water will run through the intake for the HVAC box and down the floor vents onto the carpet. Either way, these cars are known for floor boards rusting out for this exact reason.
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    Post  Sean Donica Mon Jul 17, 2017 8:50 am

    If it's leaking where it meets the firewall, would bypassing the heater core still bypass the leak? Or is that leak from rainwater? Also will disassembly and heater core replacement stop the leak if it's by the firewall? I'm not opposed to doing the work just never delved into one before.
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    Post  Kit1078 Mon Jul 17, 2017 11:12 am

    of it's leaking around the firewall, then replacing the heater core probably won't fix the problem. I would start by pulling the top off the HVAC unit and inspecting for water or damage and take it from there, since you have to pull that cover off to get to the heater core.
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    Post  GM B-Body Forum Tue Jul 18, 2017 10:55 pm

    I'm sure you already seen this if youve been searching the forum but I can gaurantee you its the heater box. Will need to be disassembled to reseal or if you dont want to do that right now, get a tube of silicone and take the screen off the box and silicone it all up on the top part, that may fix it if its the firewall gasket, however these heater boxes are separable which means the box itself can leak if the glue inside has gotten brittle and dried up. The only real way is to of course remove the whole box. https://www.gmbbodyforum.com/t46-leaking-heater-box-disassembly?highlight=Heater+box
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    Post  78i6belair Fri Sep 29, 2017 5:48 pm

    I agree here and it's more than likely the firewall to HVAC gasket that is leaking rain water.

    I went through this entire process on my Bel Air and trust me, it's a must do fix if your car is leaking water there.

    I was able to snag a whole replacement heater box assembly from a 1984 Caprice and I also grabbed the gasket as well.

    I noticed that the gasket was much thicker and made from a better material then the one from from my 78, so that might be something to look into from a donor car in the wreckers.
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    Post  JusSko77 Mon Dec 25, 2017 11:14 am

    Heater core is one location. However, don't leave out the windshield. If the top of the windshield leaks, it will run across the trim, down the a pillars and onto the floor.

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