lsintampa

1975 Coupe WITH A/C

So the astro ventilation wasn't functional on A/C cars, but the rear deck vents are still there.

I understand that there was a "system" to exit water (from washing the car or from rain) from those rear vents out the rear wheel wells.

How many "oppenings" were in those vents on A/C equipped cars.

From inside looking up, it appears that each vent depression has four rather large nipples that I presume were for draining water. All four on both vents (on my car) have been epoxied over so they are closed.

Then some really brilliant PO thought that by drilling a 1/4" hole in both vents and running a small rubber hose from the newly created hole out the rear wheel wells would suffice.

Anyway, I can't seem to find any information on AIM on that.

Thanks,

Len

Alan 71

Hi Len,
Even though your car with a/c didn't have a functioning astro ventilation system the AIM indicates the plenums still had drain hoses.
The hoses run from the side of the plenum to the upper wheel well on each side of the car.
The hoses are about 1" in diameter.
Look at UPC E-01 to E-12, Sheet 20.
Regards,
Alan

This is the typical left side drain hose…. looking high-up above the wheel well below the rear window.

theandies

My vent plenums on my '71 Convertible are outside the interior and each have a hole about the size of a quarter on the outboard back side of the plenum boxes. There are no tubes or anything. I'll actually be under my car in that area tomorrow so I'll snap a picture. Keep in mind mine may be different as we are talking about different year models and you know how GM likes to change stuff like this over the years.

Alan 71

Hi ta,
Because the plenums on coupes and convertibles are in a different location on the rear deck, the drain hose placement was different for them.
Then, when the under body change was made, the plenum drain on convertibles changed again.
As long as there were plenums on coupes they drained through hoses in the top of each wheel well.
Regards,
Alan

Block off plate on an a/c coupe… the plenums still have to have drain hoses.


Block off plate on a a/c convertible,….the plenums still have to have drain hoses.


Note the plenum is forward of the rear bulkhead.

lsintampa

OK, I understand what it should be like....

Here are two pictures of my vents... one from inside bottom looking up, the other outside along the trim.

I think someone along the ownership chain "filled" the plenums, then drilled a small hole (about the size of an air line tube for a fish tank) for draining.

My question is what the heck are the four nipples you see plugged up on the photo of the bottom???

Thanks for clarity on what I should have found.

Len




Here are the four nipples - the small hole to the left exits under the back of rear wheel well.



Vent (I think) is very shallow... my guess - it was filled in.

Alan 71

Hi Len,
O.K.
At some point the plenums were done away with and only that shallow depression in the fiberglass for the grills to fit in remained.
Someone more familiar with later cars will hopefully explain when that was.
I looked at the 75 AIM before I replied and it still shows the plenums and drains.
Was there a change DURING the 75 model year? I guess so.
Regards,
Alan

Could it be the small tubes in your photos were owner inspired?


Answers here?
https://www.corvetteforum.com/forums...nt-grills.html

lsintampa

Those four nipples line up EXACTLY where the screws that hold the grill in place are located. So I'm thinking they are plugged (so to speak) to keep water from coming in and making sure that they rust well.

Upon further inspection I can assure you there are NO holes in the wheel wells on either side.

SO, either this is how the 75 was built (an odd ball) OR perhaps an after market rear deck?

IDK...

Any 75 A/C coupes out there??






Nothing exits the wheel wells - exception the small owner added or after market drain line.<br/><br/>I inspected the under side of the wheel wells and they have no openings or signs of any openings. I'm thinking after market - BUT - the yellow paint WAS the original color... so if the rear clip was replaced it was during it's earlier life.

Alan 71

Hi Len,
Did you look at the thread I posted the link to?
It seems to explain vent situation/plenum situation.
Regards,
Alan

lsintampa

Sorry Alan, missed it, but I got it now.

End of story... I just think someone added those silly drains.

Alan 71

Hi Len,
I'd still be interested in hearing from someone about when the change took place?
Does you car's side glass have the Astro Ventilation script on it?
Regards,
Alan

lsintampa

Negative

theandies

My 1971 convertible is a non a/c car and my plenums are completely out of the rear area and I have no drain tubes. Like mentioned before my plenums have a big hole in the outboard rear corner on each plenum.
Why would Chevy make them different? Kind of strange.

stingraymax

Alan, I have a '75 a/c coupe and mine has the astro ventilation script on the glass.

Alan 71

Hi TA,
My understanding is that the position of the rear bulkhead moved.
On convertibles this change affected the need for actual rubber drain hoses for the plenum.
I continue to be unclear WHEN this occurred.
Regards,
Alan

Alan 71

Hi SM,
Thanks!
What is the build date for your car.
Is the area immediately below the grills blocked off or are the plenums there?
Regards,
Alan

theandies

Maybe we can narrow it down a bit. My '71 is a late build.
17878

502 C-3

74 A/C coupe here also. Script is on the windows but I am not the original owner.

stingraymax

Hi Alan, Build date is May 8th 1975. ( according to the trim tag E08 )
If I check thru the vin nr at corvette registry it comes up as February 10, 1975

The area below the grills are blocked and I have the script on the glass.

Hope this helps.

Alan 71

Hi Max,
To be clear…
the area right below the grills in the rear deck is completely blocked off as Len's photo shows, but you still have the script on your side windows?
Regards,
Alan

Alan 71

Hi 502,
Thank you.
Regards,
Alan