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.

[Patrick B.]

I like it when the OP reports how the topic ended, so I will report on how this ended. I asked the question about the possibility of the retaining clamps of the heater core changing over the years because my heater core did not have the rubber seal around the pipes that appeared in photos of people removing their heater cores from the firewall side.

My car was built in July 1970 and I bought it in July 1972 with about 7500 miles on it. I would not have thought that the heater core had been monkeyed with by the dealer in that time period, but that must have been the case. The clamps were identical to those in the photos supplied by Leonard. The firewall side heater box with the fan came off easily because the hard sealer had already been separated, and I am sure the lack of the pipe seal as because the dealer could not replace it. The date code of the heater core that came out was April 1970, which would be a good date for the original heater core but must have been just a coincidence when the warrantee work was done in 1971 or 1972.

The commenters said they remembered the replacement of the heater core as an easy job, but I found it not so easy. The tool made of coat hanger wire, shown in the Corvette Forum post supplied by Leonard was not nearly strong enough to remove my heater core. I made a strong tool by heating a flat screw driver and bending the end 90 degrees. It took a lot of force the remove the old core and It was damaged in the process. I practiced the replacement using the old heater core before trying it with the new one because it was so tight. I filed the firewall fiberglass to remove any interference and bent the steel of the inner heater box to get more clearance for the outer end of the heater core. I greased the inner heater box and the edge of the heater core to aid that end slipping into heater box. But, even with me standing in the engine bay (I saved this job until I had reason to remove the engine) pulling the pipe end of the heater core against the spring clamp, the only way to get the outer end into the heater box was to place a piece of wood against the outer end of the heater core and have a helper hammer it in.

Since the replacement of the heater core turned out to require pulling on the pipes and hammering on the outer tank end, I devised a simple test to let me know if I had destroyed the new heater core during installation. I got some rubber stoppers for the pipes and installed a vacuum fitting for a Mytivac hand vacuum pump on one. After the new heater core was hammered in, I was able to convince myself it was still sound since it was still able to hold vacuum.

As big a pain as this was, it was still way better than doing it on the interior side and risking damage to the 50 year old plastic trim and delicate gage cluster. None of the photos of other people doing this suggested it would be necessary to use a hammer to get the heater core in.