SwampeastMike

At first I though my '79 was missing a piece because of the 1/2" (at least) gap between the plenum and defroster duct connection. Since then I've read numerous other comments about finding the same thing.

Do any of these actually connect?

If not I have a theory of why they don't. The leaking air would, I believe, at least somewhat warm the very bottom of the windshield where the wipers park thus helping to free them when iced.

I recall reading that ice was a hideous problem with the wiper doors on the early C3s.

Is it possible that what looks like sloppy engineering is in fact a quick and dirty attempt to solve a difficult problem?

DUB

There is no need for this connection from the defroster duct to the heater box to be a precise connection. I have worked on enough Corvettes where people get in there and tape it up with black duct tape and I just laugh and rip it off.

BUT those people who feel it is going to make a dramatic improvement...tape it up.

DUB

SwampeastMike

Precise is one thing but when the ends approach an inch away from meeting it's hard to believe that the gap is unintentional :0

Every other duct connection in my '79 interlocks by inches and is sealed with closed cell foam strips.

DUB

But it does not matter due to the air is going up and the openings are the same...any air flow that is lost is quite minimal. YES..I have an air flow meter and have checked back in the day. No need to check the air flow any longer due to knowing that it is not that big of deal.

I have never had a customer in 30+ years complain that their defroster is not working fast enough.

Tape if up if you feel the need.

DUB

SPCL FX

Thank you sir! Mine not having a dash when I got it had the duct hanging sideways but if I straightened it there is about an inch gap and I've been wondering if there was something else missing! Hopefully when I begin body work I can send some pics of my 77 and get your opinion of which way would be the best way to approach the issues on the left side !

DUB

You are fine and nothing is missing. What some people may not also realize that the beater box can often times be loosen and tilted up a bit to close this gap but it is NOT CRITICAL that it is sealed. I tilt up the heater box when I am apply the heat barrier /sound deadening material I install. Because I am covering the transmission tunnel area...this 'tilting' allows me to get the floor heater duct to install easier.

Just my opinion on that...and those cars that someone has gotten in there with roll of duct tape and taped the heck out of it..I can tell you that the tape fails in time and is not sealing as like it did when they taped it up.

DUB

SPCL FX

Sorry Swampeast , I didn't mean to hijack your post ! Just realized that I may have !
Thank you again DUB ! Just learned something new , again ! The knowledge that can be found on this forum is awesome!

SwampeastMike

No problem SPCL FX!

Am pretty sure I was the first to remove the dash, saw that gap and used some duct tape to close it as best as I could. Fast forward two years and I had the dash out again for electrical enhancements and the tape (unsurprisingly) had come loose.

With all deference to you, DUB, I still wonder if the gap allows air into the upper dash cavity to warm the low windshield where the wipers park. It doesn't surprise me that the airflow from the defrost grille is nearly identical with or without its duct sealed as that duct will be the path of least resistance for the air that leaks out of the plenum.

DUB

I can understand your way of thinking but take it a step further. With the square end of the heater box...being darn near the same as the square end of the defroster duct...even if there is space between them...when air is blowing..it is going to follow the path and go from one to the other...and IF any significant air flow is lost...due to it being the defroster...I seriously doubt that you are loosing so much that it inhibits the windshield from defrosting.

If a person doubts/questions what I am saying or feels that it needs to be sealed up...do as you wish. NOT saying that anyone is. But...having worked on so many of these Corvettes. I have actually turned on the blower motor and had the defroster working while the main dash duct is still out and I can feel that the little bit of air that does not make it to the defroster duct is so minute ...it is pointless ( in my opinion) in taking the time to seal it up with tape that will fail in time...as you know it does due to it did it to you.

As for warming the area where the wiper blades rest while in the park position. That has to do with the vent in the top of the dash and how it diverts the air. On my Chevy truck..when the windshield gets icy during the winters here.....I know it takes longer to get the blades to break free if they got frozen to the windshield. But..in time with the defroster working ...everything melts and all works good because I gave the defroster enough time to heat the windshield and allow that heat to migrate through the windshield. Do not forget that you have the inside layer of glass that has to get warm.....then the plastic layer and then the exterior layer of glass that your are actually trying to warm up. that takes time. And comparing it to a new car is pointless due to its design.

DUB