Did the non-AC heater core mounting change during the C3 era?

[Patrick B.]

I have seen videos and pictures showing the heater core of C3’s w/o AC being removed from the engine compartment side without taking the interior apart. I removed the firewall heater box and the clip on the outer side of the heater core of my 70 non-AC car but the heater core will not come out. A friend sent me pictures of a 69 non-AC heater box (out of the car) showing a second clip between the tubes which is fastened to the interior heater box with two screws. These screws are not accessible from the firewall side and require the removal of the interior heater box to remove the second clip. I have seen pictures of the heater being removed from the firewall side of a 81, 74 and 72 without the complication of the second clip. Also the seal that goes around the two tubes seemed to be regular rubber rather than sponge rubber like those supplied in the heater rebuild kits.

Did the heater core attachment change sometime after 1969 or are the people who say the heater core can be changed from the firewall side working on cars whose second heater core is leaking and a prior owner had installed it without reusing the second clamp between the pipes?

Also, if the inner heater box must be removed, is it possible without disturbing the center gage cluster? Since that cluster housing can break very easily, I would probably rather have no heater than risk the cluster housing.

[Patrick H.]

I did a 72 from the engine side and did not have to remove the inner box.
It has been long enough that without seeing the car (which moved to FL) I can’t say if I had to do anything with an interior clip.

I reused some of the original seals as the reproductions did not fit well at all.

[Leonard M.]

Years ago I replaced the original heater core on a Jan, 70 LT1 from the engine compartment and only remember it as an straight forward job. This link: Heater core install done - PICS - CorvetteForum - Chevrolet Corvette Forum Discussion jogs my memory showing the hidden clip on the driver's side of the box. As you see, you have to pull the passenger side of the old core out to remove it at an angle. If you already had the interior apart, it would allow you to push the passenger side of the core toward the engine rather than pulling from the engine compartment.
I also relaced the original heater core on a 72 454 A/C from the interior and that was a much more difficult job. Doing that one had me remember how easy the 70 was in comparison.

[Patrick B.]

Leonard—- Those are great pictures in the link you found. I can certainly see how the job is done from the firewall side when the driver’s side clip is like the ones shown in the link. I think both cars pictured in the link are 72’s. They both had a large solid rubber seal around the tubes that does not look like the seal on my 70. My next question is whether the driver’s side clip on a 69-70 is the same as the 72. Does the shop manual for the 72 and later Corvettes mention removing the heater core from non-AC cars from the firewall side or does it stick to the interior approach like the 69/70 manual?

[Leonard M.]

Patrick, I don't remember any of the specific details since I did that job over 10 years ago, except; it was't that difficult, I was the first one in there and I did it from the engine compartment. I do remember the mouse nest in the blower motor and the partially eaten fan. I'd say to make a tool as shown and try pulling it out.