A/C ductwork fastener ID help?
 

This is almost embarrassing to post but would anybody be able to post a photo or two of the fasteners that support the main air distribution duct up under the dash. These two fasteners screw into the rail below the glovebox. I removed the ductwork to swap out the radio last winter. Now I want to put it all back but can’t find the #$&! Fasteners. All I remember is they have a large star washer with them. Thought I'd threaded them into the rail for safekeeping but not there. Parts manual says nada. If I know what they look like I can rummage around and see if I have something. Thanks.

That bad boy is a coarse sheet metal thread and 5/16 as I recall there is a large star washer, but it wasn't for grounding. This part of the ductwork is usually munched bad

That part of the A/C ductwork is made out of some strange stuff, like the stuff they make wax lips out of. lol

I could never place my finger on it, but you nailed it!

When I had the factory air, my screws were replaced with fender bolts and washers, that was the only thing that kept that duct off the floor.

Screws
 

Ill.show you pics of my 70 got the dash out need new one sos. But hear is pic for you. Hope it helps

ive got a bunch of those bolts & star washers from cars ive parted. you're welcome to have a couple for shipping cost if you cant find yours, just PM me for details.

Thanks for your help Bruce. I'll try some different sheet metal type screws today.

As for the star washers I assume they were to bite in and hold the plastic without having to crank down too hard on those screws. Of course almost every used duct you see has the screw notches completely torn out anyway. That whole rail across the front is just too flimsy to take any over-tightening or flexing.

Agree that this section of ductwork is generally in pretty sad shape. Combination of crappy blow mold plastic, piss poor design, passengers' big feet and Stereo Monkey installation shops just undoing the two screws at the dash and reefing on the duct without 1st checking to find the support bracket on top and the two screws attaching it to the right side vent duct. Every issue I've had under my dash seems to have a line straight back to a stereo shop in Encino CA that the original owner paid to install an Audiovox unit in 1982.

I actually found a main air duct in reasonably good shape at Norwalk on Saturday. First used one I have ever seen with both the two screw notches intact and the top section where the bracket goes not cracked or chunked out. Not perfect but very repairable and in way better condition than what came with my car.

i just sold a couple of these ducts a couple weeks ago that were in perfect condition. repros are available now too for cheaper than some of the ebay & bigger sellers out there charge for ones with cracks.

the screws are just standard sheet metal screw threads but not sure if they have the same looking bolt head. the washers are pretty standard star washers too, should be able to find them at most hardware stores or even home depot type stores.

https://www.classicindustries.com/pr...E&gclsrc=aw.ds

Going back to production, which is still the same as new vehicles, the whole dash ( ac in this case, minus the glove box insert) was put in as a sub assy. The only part off was the cross piece below the steering column. .. So.. after the
Lower 5/16 mounting, the top screws ( nuts on the right side) this ONE ugly screw was what was left. They were overtightened from the factory. There were broken ones on cars right off the truck. I wrote a report on one so we could get warranty on it. (How to piss off the delivery driver) . Probably should have had a "L" bracket bolted over they bottom.

You need a spacer in there, just tightening them down damage the wax lip duct. I used a diff bolt.
When I was putting my og radio back in, mine was cracked, year one had GM ones the shelf for $35