64 Belvedere heater box R & R questions

Getting ready to restore my heater box with new control valve, core & gasket kit, etc. Previous owner had installed a shut off valve under the hood, so I'm assuming the core is bad. Do I have to drain the radiator before disconnecting the heater hoses? I downloaded pages from the FSM but they're pretty vague & don't address this issue.
Any tips on the R & R would be greatly appreciated, so thanks in advance.

you don't have to fully drain it. just take it down below the top of the block level wise.

I also disconnected the hoses and used air to blow out the core before I pulled mine.
65 b body, so should be close.

It was nice because it was small enough that it came out without much trouble instead of the 66 and up.

since you think yours is bad, I might skip the blow out part.
Though I have to wonder unless they installed shut of valves for both lines, it might still be good, they just decided the old valve inside wasn't worth digging out?

Thanks for the info & they just put the valve on one line.Here's a pic.

Also, looking under the dash at the heater, I can see corrosion on the control valve, so maybe that's the issue & the core is actually good?
The push button vacuum switch was broken (nipples on the back), so I got a restored one & installed it. On the plug with the vacuum hoses that plugs into the switch, only one hose (red stripe on hose) was cut. I'll take & post a pic of which vacuum pod it went to.

The water valves are tough to service even if you have the parts to get it done..Pay close attention to the O ring sealing area between the valve and core it needs to be perfectly round and smooth...Some will give up trying to keep it from leaking on the floorpan and do what you have there totally shutting off the water...In my experience most times it's the valve being the problem and the core is usually good hopefully that's your case...I get the whole heater box kit from DMT and refinish the blend doors for new sealing foam and smoother operation while I'm in there..

Thanks for the info & I'll be sure to check the sealing area & O ring. Its gonna be a pain to remove the box but hope its easier than I think. Not much info on the early B's out there.

It's been a few years but Napa actually had the water valve sealing diaphragm in a kit to service the unit but as usual I had to do all the homework and provide the number of the kit..The valve's actuation pin sealing diaphragm gets old and brittle then leaks...The biggest concern there is the parts corroding and not being serviceable for the sealing duties...It was a poor design no doubt but hey, it is what it is for those years...

yeah, I would really doubt your core is bad.
that only stops water from one side. it is still a presurized system and would be spitting crap out if it were open.

It wasn't that bad to pull, but it was a lot of years ago.
3 nuts on the firewall you can see.
maybe a mount near the radio.

I have taken too many out, so I don't remember, but don't think there is a fresh air vent to unhook.
then just the cable to the valve on the box.

didn't even have to pull the front seat. It slid out under the dash.
Don't even remember unbolting that corner like you do for 66 and up.

It's been a looong time now, but having had about 17 of the 64 Plymouths, I used to have recurring problems, and the control valve was on that list.

Drain it down, or just wire the hoses to hang above heater level, vise grip, etc.

IIRC, removing the radio first may have eased clearance problems, but for the most part it is a pretty easy job, once into it you will have it out in short order.

I'm with the other guys on the shutoff, My take on it is that it was being used to control flow thru the core, as a shutoff in one line won't stop coolant from occupying the core, so the valve probably isn't (wasn't) leaking either.

And, may I say, that is a great looking engine compartment, most of mine were much worse, (and much newer!) back in the day ... color is the same as VT state police used, had a few of those too.

A huge thanks for all the info & advice and I'll start on it today while the seats are out to the upholsterer. Its a no rust survivor & even have the orig certicard. Orig 383 runs great but has some blowby issues from a couple of cylinders (broken or stuck rings), so it'll be coming out soon for a stock or stroker rebuild.