1967 with C60 - Problem removing heater box assembly from under dash

[Scott S.]

appears to be on the engine bay side of the firewall, going through to the inside firewall, where it is secured by a nut and washer, but it's NOT. I can turn the nut from under the dash, but it is just turning the bolt at the same time, it's not loosening. When I stand in the engine bay and have someone else turn the nut (and bolt with it), the head of whatever I'm looking at in the engine bay (red arrow in pics below) is NOT moving, so the other end of the bolt attached to the nut we're turning must be nearby, toward the passenger side of the car, between the engine bay side of the firewall and the interior side of the firewall.

It doesn't really look factory. Not the "head" that I can see on the engine bay side of the firewall, and not the bolt-end and nut under the glove box area on the interior side of the firewall. Before I cut this bolt, can someone tell me if this is a factory part, and if so, how do I get to it in order to hold the bolt-head secure, to keep it from spinning when I turn the nut?

I haven't found anything about it in the Chassis Service Manual, and so far I haven't found anything about it in the AIM (C60, A1-5). All of the diagrams are a three-quarter view from the opposite side, as if looking from the driver's seat.

Thank you,

Scott




Picture 1: Engine bay side, the arrow is pointing to what looks like a giant rivet-head - I thought this was the head of the bolt that sticks through to the interior, but it doesn't move when the nut-and-bolt and turned from the inside, so the actual head of the bolt I'm searching for must be slightly to the Left, somewhere behind the fiberglass.

Picture 2: Same shot as Pic #1, closer up without camera flash, to show the concentric circles around raised "dimple" on the giant "rivet" head (what is that thing?)

Picture 3: actual interior bolt-end with attached nut that I can't find the "bolt-head" for; I can turn the nut, but it is frozen to the bolt and turns the bolt with it. Can't find where the "head" of this bolt is located.

[Larry M.]

Re: 1967 with C60 - Problem removing heater box assembly from under dash

Scott:

I'm guessing here, because I don't know for certain. I have not had my AC box out of the car. We need someone who has removed and reinstalled his 1966-67 AC box to comment.

The "bolt with the rusted nut" may actually be a stud with a forged/stamped intergral nut (ie. one piece ). I have seen these before. The engine compartment end that you cannot find may be the "big rivit head" that you show, which was drilled and tapped on one side by someone so that it would serve as an oversize fastener. Possibly because the fiberglass was damaged or the normal bolt hole was grossly oversized.

Hope this makes sense. If I'm correct, you should be able to completely unscrew from the cabin side......or you could drill out or grind out the head of the "large rivit".

Larry

[James W.]

Re: 1967 with C60 - Problem removing heater box assembly from under dash

Scott,

Going from memory when I removed the heater box from my 1965 with A/C a few years ago, the picture of the rusty stud with the nut attached to it will need to come off of thestud before th heater assenbly will come out. The nut that is on there is similar to the stamped/nut used to attached the fender emblems. First I'd remove the right side vent cable and bracket so you can get a clear shot at it I'd get some Kroil or PB Blaster and soak the threads. If the stud want to turn, you may need to try and hold it at the very tip with a plyers or vise-grips and turn the nut with a box end wrench. You can clean the thread back up with a die nut or cut a small or grind a small portion of it off when you go to reinstall the nut. I know it's not easy wor ing in there but it will come off. Have you taken the center nut loose from the stud under the center of the dash that hold the left side of the heater box to the firewall? That one is bear to getat also. As I remember on that one all you have to do is loose the nut, the faster fit at that side of the heater box is slotted and does not require you to remove the nut from the stud.

I hope I'm helping you in some way.

Best Regards,

James West
Omaha, NE.

[John H.]

Re: 1967 with C60 - Problem removing heater box assembly from under dash

I haven't found anything about it in the Chassis Service Manual, and so far I haven't found anything about it in the AIM (C60, A1-5).

Scott -

The threaded stud in your photo is part of a bracket that's riveted to the engine side of the firewall; it's shown in C60, sheet D2, item #3. The attachment of the inner case to that stud with the nut is shown in C60, sheet A2, item #3.

[Scott S.]

Re: 1967 with C60 - Problem removing heater box assembly from under dash

Hope this makes sense. If I'm correct, you should be able to completely unscrew from the cabin side......or you could drill out or grind out the head of the "large rivit".

Larry

It definitely makes sense Larry. My automotive vocabulary is getting better (slowly), but I didn't know what else to call that big rivet-head looking thing besides a large rivet
Thank you!

Scott,

Going from memory when I removed the heater box from my 1965 with A/C a few years ago, the picture of the rusty stud with the nut attached to it will need to come off of thestud before th heater assenbly will come out. The nut that is on there is similar to the stamped/nut used to attached the fender emblems. First I'd remove the right side vent cable and bracket so you can get a clear shot at it I'd get some Kroil or PB Blaster and soak the threads. If the stud want to turn, you may need to try and hold it at the very tip with a plyers or vise-grips and turn the nut with a box end wrench. You can clean the thread back up with a die nut or cut a small or grind a small portion of it off when you go to reinstall the nut. I know it's not easy wor ing in there but it will come off. Have you taken the center nut loose from the stud under the center of the dash that hold the left side of the heater box to the firewall? That one is bear to getat also. As I remember on that one all you have to do is loose the nut, the faster fit at that side of the heater box is slotted and does not require you to remove the nut from the stud.

I hope I'm helping you in some way.

Best Regards,

James West
Omaha, NE.

Thanks for the reply James, it does help. I have never done this before so I'm grateful for all replies. If I understand you correctly, I have not yet taken the center nut loose from the stud under the center of the dash, I haven't even removed the "T" shaped dash-pad and center console yet (3894580 Pad Asm. Chart RH, 3861793 Pad Asm Chart LH, Instrument Panel, UPC 1ASM / E1).

That's next, probably should have been done first

[Scott S.]

Re: 1967 with C60 - Problem removing heater box assembly from under dash

Scott -

The threaded stud in your photo is part of a bracket that's riveted to the engine side of the firewall; it's shown in C60, sheet D2, item #3. The attachment of the inner case to that stud with the nut is shown in C60, sheet A2, item #3.

Thanks John, I see it now.

Since I'm looking at the page (C60-D2), it was also pointed out to me that the recirculating duct housing (to which the "Blower & Evap. Asm." box attaches) is stamped full of holes like swiss-cheese, which it should not be (see picture #1, it looked uniform enough that I thought it was supposed to be that way). Since a replacement for that interior metal housing is probably hard to find, I can remove it and weld the holes closed.

Any idea why someone would have gone to the trouble to stamp holes in it like that?

[Ray G.]

Re: 1967 with C60 - Problem removing heater box assembly from under dash

Thanks John, I see it now.

Since I'm looking at the page (C60-D2), it was also pointed out to me that the recirculating duct housing (to which the "Blower & Evap. Asm." box attaches) is stamped full of holes like swiss-cheese, which it should not be (see picture #1, it looked uniform enough that I thought it was supposed to be that way). Since a replacement for that interior metal housing is probably hard to find, I can remove it and weld the holes closed.

Any idea why someone would have gone to the trouble to stamp holes in it like that?

Hello Scott;
Appears from your description the nut may be stripped on the stud. Drilling the head off may be your best solution to preserve the housing.
My guess on the the drilled extra holes is someone was trying to get more air flow and/or stop the evaporator core from frosting up in humid climate conditions.
Hope this helps.
Ray

[Scott S.]

Re: 1967 with C60 - Problem removing heater box assembly from under dash

Hello Scott;
Appears from your description the nut may be stripped on the stud. Drilling the head off may be your best solution to preserve the housing.
My guess on the the drilled extra holes is someone was trying to get more air flow and/or stop the evaporator core from frosting up in humid climate conditions.
Hope this helps.
Ray

Hi Ray,

I wasn't focusing on the section with holes at the time, and it's in the shadows (garage is kind of dark where the body currently sits). I found a closer-up picture of the section with the holes, and it looks like someone went to a lot of trouble here.

The holes are even stamped along the bends in the piece (picture below, blue arrows), when it would almost certainly have been easier to stamp holes just in the flat areas. Also, there appears to be at least seven weld marks (red arrows). If none of this is factory, then somebody was sure trying hard to accomplish something.

As for humid climate conditions, I don't know. I found out from the NCRS Shipping Data Report that the car (Jan. 11 production date) was originally sold at Potamkin Chevrolet in Philiadelphia. I was able to talk with the previous owner last December, he bought the car in 1972 in Baltimore when he was stationed at Fort Meade, moved to Ohio and drag raced the car for two summers (B stock). He removed the factory A/C components from the engine bay to save weight and horsepower, fabricated his own heater block-off plate (if I understood him correctly), and included all of the original parts in boxes when my father bought the car in 1976.

This past summer I found an old (non-A/C?) heater-assembly in the garage attic, with an aluminum cut-out block-off plate riveted onto it. I'll try to take pictures of it and post here tomorrow, it might provide more clues to this puzzle.

Thanks for the reply Ray,

Scott

[Scott S.]

Re: 1967 with C60 - Problem removing heater box assembly from under dash

Here are some pictures of the outer firewall heater box assembly I found in the garage. I think this is probably the cover used by the prior owner when he removed the A/C components from the '67 for drag racing, due to the aluminum plate riveted onto the box near the blower motor - but it is possible this part was from my father's first Corvette (1966) which he bought in 1974 or 1975, the year before he bought the '67. I found several 1966 parts in the garage attic (along with '67 parts), including a '66 power antenna, '66 gas lid and the '66 chrome seat belt bracket that mounts to the end of the center shifter console.

Inside the heater box it says P/N 3156854 with "L" over "NOR" over "C", but no ink-stamped dates. I checked the part number in the archives, and it is mentioned twice, once regarding a 1963 and the other was for a '67.

[Page C.]

Re: 1967 with C60 - Problem removing heater box assembly from under dash

Hi Scott,
Enclosed are a couple of photos of a midyear air box. I believe the stud you are seeing is as John and James have indicated. Its a stud that is riveted to the firewall that has come unattached to the app. 1/2 inch by 1 1/2 inch piece of metal that is riveted to the firewall with the stud facing into the passenger compartment. You mignt take a dremel tool with a narrow cutoff wheel and make a slot across the rivet head so that you can hold it with a screwdriver. After you get the nut loose of the passenger side and get the box removed, you can remove the bracket. Weld up the slot you made and weld the stud back to the bracket. Also remmeber what James said about the stud on the other upper corner of the inside box. You can hardy see it and tough to get too, but you only need to loosen it as the bracket is sloted.
Enjoy your post. Also if you need any photos, let me know.
Page Campbell
pcampbell3618@comcast.net

[Scott S.]

Re: 1967 with C60 - Problem removing heater box assembly from under dash

Hi Page, thank you very much for the reply and the pictures. We need to remove the dash-pads and center console anyway, so that should make it easier to get to the other stud on the LH side of the heater box. Now that I understand better what the problem is with the RH corner stud, we should be able to get it apart with one or another of the methods mentioned above (thanks to all!). I'm interested to see what date is stamped on the inside of the heater box assembly, it's one of only a few remaining unknown dates that I'm aware of on the car.

Does anyone have a picture of what the swiss-cheese interior of the duct-housing on the engine bay side of the firewall is supposed to look like, without all the holes stamped in the metal? I have not been able to find a correct picture of it anywhere so far (referencing picture in Post #8).

Are the multiple weld-spots factory, or was that post-production too?

Thanks again,

Scott

[James W.]

Re: 1967 with C60 - Problem removing heater box assembly from under dash

Hi Page, thank you very much for the reply and the pictures. We need to remove the dash-pads and center console anyway, so that should make it easier to get to the other stud on the LH side of the heater box. Now that I understand better what the problem is with the RH corner stud, we should be able to get it apart with one or another of the methods mentioned above (thanks to all!). I'm interested to see what date is stamped on the inside of the heater box assembly, it's one of only a few remaining unknown dates that I'm aware of on the car.

Does anyone have a picture of what the swiss-cheese interior of the duct-housing on the engine bay side of the firewall is supposed to look like, without all the holes stamped in the metal? I have not been able to find a correct picture of it anywhere so far (referencing picture in Post #8).

Are the multiple weld-spots factory, or was that post-production too?

Thanks again,

Scott

Hello Scott,

You mentioned above about removing the dash pads and center console. I hope their removal is because you are replacing them. The dash pads don't need to be removed and the center console chrome surround will need to come out to make it easier to remove the heater box.

Have you removed the radio, clock and the defrost, fresh air and the a/c cables along with the a/c under dash duct work that goes to the left side of the car? That will need to come out/off before the heater box can come out. I took lots of pictures of the components as they are installed in the car before removal and used the AIM diagrams and wrote notes on them as to what sequence each piece came out and the routing of the cables that run to the heater, a/c and fresh air vents. Somewhere I may have saved the pictures I took while doing work on my '65. I'll see if Ican dig them up.

Regards,

James West

[Scott S.]

Re: 1967 with C60 - Problem removing heater box assembly from under dash

Hi James,

The body is off the frame, and the only thing that hasn't been completely disassembled yet is the dash / under-dash area. The dash pads are in great shape, the radio and clock have been removed, and the ductwork with the chrome vent-balls (both sides) and "Y" diverter have been removed.

Are there reasons NOT to disassemble the dash? The interior firewall insulation needs to be replaced, and everything else up under there ought to be checked out (will also be installing all new wiring harnesses). I remember reading something about addressing a potential windshield wiper transmission issue that should be checked, but I will have to look it up again. Can these things be done without taking the dash pads and center instrument panel out?

[James W.]

Re: 1967 with C60 - Problem removing heater box assembly from under dash

Hi James,

The body is off the frame, and the only thing that hasn't been completely disassembled yet is the dash / under-dash area. The dash pads are in great shape, the radio and clock have been removed, and the ductwork with the chrome vent-balls (both sides) and "Y" diverter have been removed.

Are there reasons NOT to disassemble the dash? The interior firewall insulation needs to be replaced, and everything else up under there ought to be checked out (will also be installing all new wiring harnesses). I remember reading something about addressing a potential windshield wiper transmission issue that should be checked, but I will have to look it up again. Can these things be done without taking the dash pads and center instrument panel out?

Hello Scott,

In my opinion there is no reason to remove the dash pads or any part of the center console. Once the gauge cluster, radio, clock, vent cables, gloves box and heat/air conditioning components are removed you should be able to replace the firewall insulation, wiring harness, and service the windshield wiper transmission and wiper arm without any interferences from the dash or dash pads.

I am working with a fellow NCRS member who is performing a restoration of a '65 396 Corvette. The dash pads in the car are perfect and I advised him that there is no reason to disturb them. We simpley cleaned the dash pads ans center console with a mild cleanser (Simple Green) and then wrapped them in plastic during the painting portion of te restoration.

Regards,

James West

[Scott S.]

Re: 1967 with C60 - Problem removing heater box assembly from under dash

Thanks very much James, I'm sure the dash pads and center console would like to stay just where they've been for the last 43 years. It looks crowded up under there. I didn't realize those things could be accomplished with the dash in place, but that's good news.