it is finally time to replace the original cardboard heater plenum. i have a shiney new brown plastic one,,, but seems to me that there should be something (a gasket? short connecting tube?) that goes between the square end and the same size opening by the fire wall.

thanks!

 

What year mustang do you have, and do you have air conditioning?

 

Only photo I have of a defroster plenum. It attaches to the back/side of the fiberglas heater box.

 

it's a 66 no air conditioning....

great photo JamesW! - mine looks identical, but there's about 4 inches space, where yours lines up nicely. will have to check carpet, etc. getting in the way of it lining up correctly.

 

I bet it's the defroster deflector, that's the only cardboard item on the heater.
Jim

 

it should slide up. Make sure all your old cardboard is gone. It should mount with small sheetmetal screws.

 

Correct, 2 on the inside and 2 on the outside. Ford p/n 42119-S2, 8-18x3/8 hex head with a small flange, phosphated , not zinc plated. Jim

 

just replaced mine a couple of weeks ago, it was a tight fit but it finally slid onto the receiving end and srcewed it down, be patient and good luck : )

 

I pulled the carpeting down out of the way and that made the alignment issue much easier.Since the friction fit was pretty good, Iwent with two screws...just too hard to get at the back ones. Maybe this year I'll try again with different tools.