[Trevor78]

The heater box is under the dash so the seal is also on the dash side to seal heater box to firewall. #3963725. There's nothing on the engine side, just the heater core pipes coming through, each with a sponge seal around them as well.

Some sell a reproduction, otherwise just use close-cell neoprene with adhesive backing on 4 sides.

Random ad.

https://www.chicagomusclecarparts.co...amaro-trans-am

[GoreMaker]

I consider it an important part of the installation. If it wasn't there before and you didn't mind, then I guess you can leave it that way. It significantly improves the performance of the heater, and especially the AC if you have that, plus it really cuts down on noise and smell from the engine bay. My old one was damaged from old age, so I made one by cutting out a rectangle from an adhesive-backed foam insulation sheet
https://a.co/d/1OXXmdk

[Trevor78]

Some more diagrams.

Firebird AC heater box ducting evaporator case assembly diagrams (1) by Ben, on Flickr

Firebird AC heater box ducting evaporator case assembly diagrams (2) by Ben, on Flickr

Firebird AC heater box ducting evaporator case assembly diagrams (3) by Ben, on Flickr

[GoreMaker]

Not shown in that diagram, the AC box in the engine bay uses that gooey butyl rope seal around the periphery that presses up against the firewall, and between the two halves of the box. There's a channel in the mating surface to accommodate it. Those seals are VERY important, otherwise the AC performs like crap.

[Trevor78]

I only added pages for what was being discussed. Yes, the case is right next to the exhaust, any gaps introduce more heat straight into the AC, and cabin, fumes, sound, ants...! Any gaps will allow the fan to suck air from the easier route, the hot air gap next to it rather than through the evaporator of cold air.

[nUcLeArEnVoY]

I'm reassembling my heater box right now as well due to an original heater core leak, I went with Ames' copper/brass repro and it seems to be a quality unit and held vacuum when I tested it.

Chicago Muscle Car parts does have the seal kit in stock, I bought it myself and it looks good. Only thing is, there is not adhesive on the seals so you need to apply spray adhesive. Not really necessary for the heater core pipe seals since they fit snugly around the pipes, but the square gasket definitely needs spray seal. Just bear in mind that Chicago Muscle Car parts doesn't do online orders, you need to call them. They ship pretty fast.

As expected, my orange vacuum tube going to the heater side nipple of the push/pull actuator was crumbled to nothing; and the actuator itself was so rusted on the inner nipple that same orange line was hooked to that it was beyond serviceability. Had to replace that, too.

The mounting stud that is clipped onto the corner of the heater box with the integrated ground strap was also bent beyond serviceability on mine, luckily they sell repros of it on eBay, but without the ground strap, so I got a generic groundstrap of appropriate size from Falconer Electronics. I had to relocate the large eye that used to be part of the mounting stud to the lower mounting screw instead (the one you unscrew from inside the car). The ground strap is very important.

Also make sure to replace the foam layering on the defrost diverter door. From the factory, the foam layer is stapled on (thus the staples you see). I had to pry off the staples and install adhesive foam I got from BlendDoorUSA. It's high end stuff that isn't biodegradable like the stock stuff was. And yes, you do need to cut out the two holes in the foam to match the two round holes in the diverter door. Those two holes are the "20%" of air the windshield and/or floor vents get respectively depending on the settings that the service manual is talking about.

While you're at it, you may want to replace the heater hose nipple at the rear of the cylinder head if you're running a Poncho motor. The later design uses a rubber restrictor rather than the bimetallic coil the older ones used to restrict coolant flow to the heater core. When I removed mine, the rubber was missing and that's probably because it had disintegrated over 45 years as it was the original nipple. Without some degree of restriction, the heater core is subject to earlier failure due to the slugs of water overstressing it during heavy throttle. Another option is to just place a .200 restrictor inline somewhere in the inlet heater hose going to the core from the back of the head. That's what they installed on the police car packages.

[Trevor78]

Probably all engine types had their version of the retrictor fitting in Firebirds since there was no heater tap valve. I was only just posting info and pics of the Olds version on another forum.

[i4abuygto]

I appreciate all the info- As much as I would rather not, I will be pulling the heater box out and sealing it correctly.

By the looks of the helpful links and photos, I am missing the seals around the water intake pipes also.

I noticed I only have one seal for the intake tubes - I have the one that mounts to the housing under the hood. It looks like I need to have two other round seals that slide over the intake pipes sandwiched between the box and the firewall.

You guys are very helpful

Thank you

[i4abuygto]

On my 79 TA, I finally found time to remove the newly installed heater box and I installed a seal against the firewall.

As Murphy would have it, I broke the lower stud behind the passenger side head when reinstalling the heater box. I didn't think it was that tight when the stud broke but obviously - the king of overtightening strikes again.

Does anyone have any ideas on finding a new stud?

Any recommendation on just leaving it with only the two mounted studs and nuts. I am sure you the seal will not be uniform around the blower housing with only two studs holding.

Has anyone delt with this and what is the fix?

Does anyone have a torque spec or recommendation on the housing stud nuts?

Thanks guys.

[nUcLeArEnVoY]

Which stud are you talking about? One of the two that are integrated/welded into the metal frame of the heater box, or the one that is clipped onto the outer edge and has the integrated ground strap?

If it's the latter, they reproduce it and you can find it on eBay. I had to replace mine with this one because I bent mine beyond accepting the nut along the entire thread: https://www.ebay.com/itm/393981832146

The only problem with the repro one is that it doesn't include the ground strap, which is extremely important since it prevents the coolant from degrading the heater core via electrolysis. What I did was just purchased a generic groundstrap (roughly 5-6") and relocated the large eyelet to the bottom mounting screw for the heater box (the ones with the teethed washers that you access from inside the car).

As for the ones that are part of the metal frame, there is a guy on YouTube that goes over replacing the heater core for his 1980 (or 1981, not sure) and he runs into the same issue and describes what he did.

[i4abuygto]

Which stud are you talking about? One of the two that are integrated/welded into the metal frame of the heater box

It is the lower one that is integrated into the heater box - I haven't removed the box yet so I don't know exactly what is there to work with on the broken stud. I know the stud broke right at the base of the nut which means I should have some bolt there to work with.
I thought about just welding a good 1/4" threaded stud to the broken stud. Or, maybe JB weld it and rethread it.
These studs must not take much to tighten- I hardly put any torque on it when I was tightning it down.

As for the ones that are part of the metal frame, there is a guy on YouTube that goes over replacing the heater core for his 1980 (or 1981, not sure) and he runs into the same issue and describes what he did.

Thanks, I will try to find this YouTube video.

[Trevor78]

Some of those studs were threaded into the plastic of the box but if you snapped it then along with the nut was probably half eaten away with corrosion at that location. If part remains you could create a tube-nut sleeve, thread it onto the portion, thread a new stud extension into it with loctite. Then when tightening it all up just don't swing off it too much!

[i4abuygto]

If part remains you could create a tube-nut sleeve, thread it onto the portion, thread a new stud extension into it with loctite. Then when tightening it all up just don't swing off it too much!

If the broken part of the stud is right at the fire wall would the nut sleeve not allow the box to fit tight to the firewall?

I will remove the box today to see what I am working with.

[i4abuygto]

Thanks all for your help - this is how I fixed the broken stud issue.

I had about a 3/8" long remaining stud left that was broken at the firewall so I didnt think I would have enough clearance to put the Tube nut sleeve idea in place. The tube nut would have be larger than the bolt and would have been difficult to work with the existing holes in the firewall.

So per the video idea earlier

As for the ones that are part of the metal frame, there is a guy on YouTube that goes over replacing the heater core for his 1980 (or 1981, not sure) and he runs into the same issue and describes what he did.

I air ground the stud flush and drilled out on center to tap a 1/4 - 20 thread in the aluminum through the ground off bolt. I threaded a stainless steel nut onto a 2" stainless steel 1/4 -20 screw and ran the nut to the screw head. I followed the nut up with a stainless steel washer. The Idea here is to use the nut as a jamb nut threaded against the tapped hole in the aluminum.

I threaded the screw in from the inside of the case out after putting locktite where the screw and nut threads would end up. I was careful not to put the locktite further out as I didnt want it where the case mounting nut will thread.

After threading the screw in up to the washer - I held the screw and jammed the nut by tighting toward the threaded hole to jamb the screw tight so it will not turn when threading the mounting nut on.

Thanks all for your ideas and help.

[Trevor78]

Good Job.
Yes, you'd likely have needed larger hole at firewall or outer case if it had to fit more than stud diameter. That's easy to cater for if needed.