Defrost duct

[Gregk]

Hello everyone this is my first post.
I have a 78 gmc that I'm trying to get the heat and a/c working in. After replacing the leaking heater core and getting the hvac box bolted up, I noticed the bottom of the defrost duct doesn't line up with the top of the box, there's about a 1 inch gap as you can see from the photos. I'm not sure what I'm doing wrong or if there is a missing part that should go there. I know I could use tape to seal it off but I'd rather not do that if I can help it.

Any advice would be appreciated. Thanks .

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[Originalthor]

I had the same thing and made this. Worked way better.

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[Chevy 88]

You could always try expanding foam. It seals up large gaps really well, and you can easily trim it away as needed.

You really need to follow the directions on the can though, or things can go bad.

 

[mxer147]

Mine looks similar, I am considering adding some plastic attached with rivets and the silver duct tape. Might work on that tomorrow and if I do I will post a few pics.

 

[ali_c20]

Welcome from Austria.
Same on my K5, I made a sleeve out of abs plastic.

 

[cutoffkay]

Welcome

 

[Gregk]

Thanks to everyone who chimed in. I ended up using foam all around and it seems to be working so far.
I don't understand how the guy who designed this thought it was a good design.

 

[KenHen]

I'm sure tape, foam, or similar fixes work fine. Mine had a gap and was offset, so I made a simple sleeve with my 3d printer. It also solved the problem of giving a place for the screw to be useful. The Forum won't let me attach the STL file, if you can use it let me know. I used ASA filament, I don't think PLA would last long with the temps.