Rebuilding the Heater Box

One of the first things we tied to do when we first got the car was rebuild the heater box. We bought a new heater core and tried to replace the vent door foam; however, at the time finding parts for this car including simple things like gaskets and foam was difficult and somewhere along the way we stopped working on the heater box. Now, several years later with new online aftermarket companies like Detroit Muscle Technologies, we can finally get those last few pieces we need.

But first, the heater box itself needs some TLC.

Now, if your mid-60's A-body heater box is like mine, the passenger side vent door rivets pulled out of the fiberglass many years ago. When the rivets pulled out on my heaterbox, they took chunks of fiberglass with them, so I couldn't just use new pop-rivets. Instead I opted for a simple backing bar to repair the vent door. I took a piece of 6061-T6 Aluminum bar stock and used a manual mill at a friend's machine shop to square it up and drill+tap two holes in it the same spacing as the original rivet holes on the vent door. I milled the bar to a length that would just fit between the two fiberglass support gussets (see the picture on the right) and fastened the vent door to the backing bar with two stainless button-head cap screws. The button-head cap screws are nice because unlike rivets they can be removed if I ever have to do repairs on the heaterbox in the future and with the butten-head they look like rivets at a glance.

Diligent use of Rust-Oleum black rust reformer spary paint (rebuilding fluid) makes these internal mixing doors and fasteners look better and should stop them from rusting in the future.

Getting ready for final assembly, I have a new heater core and have rebuilt or scavenged all the parts I need. I went ahead and got a package of 65-67 Mustang heaterbox clips as they were close enough to the original clips in size, are readily available for cheap and they did work. The blue cardstock backing material is in fact thick blue gasket stock we got in a roll from a local auto parts store and cut to match the original cardstock as it was beyond reuse.

The vent door foam and foam ring seal for the air-inlet came from Detroit Muscle Technologies. Unfortunately I installed the heater box in the car before I could get a picture of it.