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Heater Box rebuild

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I'm rebuilding the heater box on 6S1534 and was hoping for some guidance/insights from the group.
The box itself is in pretty good shape with just a couple of small cracks in it and a small piece missing where the heater hoses enter (Pic 4). It still has the FoMoCo stamping on it (pic 5). The interior foam has all but disintegrated and the internal metal boxing with the flap that sits adjacent to the heater core (Pics 2 and 3) has light surface rust and some minor pitting but is still fully functional. The plenum chamber is made of cardboard material but I think is beyond saving.
The demister tubes are a paper type material with cardboard where they attach to the top of the dashboard. Interestingly they are square shaped (Pic 1) and not round like the reproduction parts I have seen online. They don't have any rips or tears and aside from being dusty seem ok. I'm fine to re-use them but am curious as to whether they are a genuine part or not.
I was wondering about the following:
  • How do I best go about cleaning the internal metal box & flap unit? Light sanding gets alot of the surface rust off but I cant get into the tiny areas around the flap rod.
  • What is the best way to repairs the minor cracks in the heater box itself? (see pics 4 and 5)
  • How is the foam held in place? Adhesive or double sided tape etc?
  • Has anyone seen these square type of demister hoses before - are they original ones or replacements, possibly done many years ago? Does anyone have any pics of the real things so I can compare?
Appreciate any advice or insights

Pic 1.jpg

Pic 2.jpg

Pic 3.jpg

Pic 4.jpg

Pic 5.jpg

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This forum is more oriented towards the modern 2006+ Mustangs.   You'll find a lot more people with experience in this area at the saac forum.   www<dot>saacforum<dot>com  (this forum software suppresses this link).    They focus on the 60's Mustangs. 

Edited by twobjshelbys
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If you just go to Google and type in 1964, 1965 or “1966 heater box rebuild video”.......there are literally dozens of videos that will come up that will walk you through the process. You can go through the P.I.T.A. of rebuilding it if you are striving for some kind of concourse type restoration, or you can go to CJ Pony Parts or any of several Mustang supply houses and they have complete Heater boxes available for around $200. Demister hose kits are around $50. Back in the 1980’s when I had my 1964/1/2 Mustang I was restoring it to drive and I rebuilt mine, then a few months later the motor burned up and I had to yank it again and replace the motor and reinstall, then about a year later the heater core sprung a leak and I had to yank it out again, repair and replace... Back in the day it was a labor of love, in hindsight it was a P.I.T.A.....if I was doing it today I would just buy a New Complete box, store the old parts in the attic to sell whenever I decide to sell the car ......... and call it a day. To each his own.

In regard to the fiber glass cracks, those can be tricky, If you just build up the repaired areas with resin/gel they won’t last. I would suggest put down a resin coat then some fiberglass mat for strength and some more resin coats over that. Then some sanding and painting.................enjoy.


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Thanks to both of you.  I'll check with SAAC too. Appreciate the tip re fiber glass.she is certainly no concourse machine - I love a spirited drive.  I guess I'm still in the labour of love stage...  For now.

thanks again.

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On 4/20/2020 at 8:55 AM, 66shlby said:

Thanks to both of you.  I'll check with SAAC too. Appreciate the tip re fiber glass.she is certainly no concourse machine - I love a spirited drive.  I guess I'm still in the labour of love stage...  For now.

thanks again.

Best of luck, post up some pics from time to time of your progress. Always nice to see and hear about an  old Shelby restored or brought back to life.

Edited by mhr1961
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Hey 66shlby,  years back I redid my 64 Vette’s fiberglass heater box and used the fiberglass mat with the resin/gel too, just like one of the other members mentioned.  But, please be aware there is a couple of different variations of fiberglass mat that you can use.  One kind of mat that you might find in a kit forum in a automotive store is like a fiberglass mesh type or you could use the real McCoy the fiberglass mat.   The true fiberglass mat is what a good buddy of mine always used to build and fix all his projects and molds of new cars, of which there was many.  When cured,  for as light as fiberglass is, it’s super strong and the glass mat can be cut usually with just a scissors.

Hope this little bit of info helps, and good luck with your project too!   :peelout:

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