Im posting this up as I applied stuff that I found posted in forums and wanted to share with others. I have a 71 Chevelle with 307 in it and a/c. The heater core went out a few days ago, throwing up on the carpet I just installed about two weeks ago.
The weather dropped into the 30's and I got chilled. Im not done with this repair, but I think I got a good jump on it and I found that it really wasnt all that bad going at it ..well not yet anyways. Im to the point to where I have the heater core box removed and only have to get inside of it to put the new one in. Pretty good progress considering I dont have a garage and it was cold out.
Hopefully, someone can use this thread. Sorry about it being long winded, but I want to be as descriptive as I can to make it more visual and easier for you. Im not a certified mechanic, just and older guy with his tools and his Chevelle...
I started by disconnecting the battery. I knew at some point I would be working under the dash board near some wiring.
I removed the passengers side front wheel and dropped the inner fender well down. I removed everything but a few of the forward end bolts about where the battery tray mounts. This allowed more than enough room for me to work along the firewall.
I then removed/destroyed the heater hose connections where the came out of the fire wall for the heater hoses to connect to. I say this because
no matter that I completly loosened up the tower type hose clamps, the hoses would not come loose. I used a retractable bladed cutter, I cut the hoses loose. . I ended up cutting the hoses up near the lower edge of the old clamps. Then using a screw driver and a few choice words, I pryed and bent up what was of the old connections/throats of the old heater core and got the remaining peices of hose off..It was tight working in there.
Keep in mind, no matter how much I reminded myself of the A/C hose connection there at the plenum, I still found myself leaning on it for a better angle of attack. Be careful so as not to break something else when trying to make a repair.
Now what I mentioned earlier about bending up/flattening out those heater core peices that were sticking out from the firewall. This will come up in a few minutes. I took my shop vac and placed it over each heater core throat and drained out any remaining antifreeze that might be left inside of the heater core.
As listed in other threads, the bolts that attach the heater core housing inside of the car under the dashboard/glove box area have heads that go from the inside of the car and they are secured by nuts on the compartment area of the engine firewall side. These bolts, if you will, are flattened round heads that enter through a clip that clips along the lip of the heater core housing in four places. Where these heads attach to the clips are one solid peice anchored on to the core housing box. Passing through the firewall to the engine compartment are the threaded portions/posts that the nuts on the inside of the firewall attach to.
Looking at the face of the heater core box where these four bolts heads are along the lip of the box, it will look like a circle inside of a slightly larger square. The square is actually the clip mounting onto the lip of the box. These clips dont turn, the only thing that moves to seperate them from the fire wall is the nut on the opposite side of the firewall when you are removing them.
The nuts are 7/16. Look for the first one next to where the throats of the old heater core are coming from the firewall into the engine compartment. There should be one up and to the right of where the larger hose connected to the core. This is the easiest one to get to. Just loosen the nut off completely. Dont try to push the rest of the bolt through the firewall because it is attached to the clip on the edge of the housing inside(mentioned above) , no matter how much you push/bang on it, its not going to happen because the other 3 are holding the housing against the inside of the firewall.
The next one is at the bottom of the plenum housing almost directly inline with the one you just removed. You went through the hassle of removing the inner fender and this is how you access this one. It is near the lip of the plastic plenum for the a/c along the lower left edge. You can get to it from top side, but it is easier to wedge your hand and that 7/16 box wrench in there to get the nut off.
I forgot to mention, there is about an inch of threaded bolt that extends out from the plenum on all four of the screws that these nuts attach to. It might help you locate them.
The third one is along the upper right corner of the plenum box. Look for the same 7/16 nut. This nut is pretty much in line with the first one you removed off to the left upper corner of the plenum where the lines come from the heater core. Im guestimating that there is about 18-20 inches spread between the first and third one (horizontal plane).
The fourth one is located near the lower right edge of the plenum. Also about the same distance as the first and third one were. It is also pretty much in a horizontal plane with the second one (on the lower left edge) This fourth one is on the firewall side of where the base of the valve cover is. Imagine that base of the valve cover extended to the firewall and you will find it. I found that it was easier to get to by removing the vacume ball (lack of better term) big black round thing that has vacume lines running to it. It is held in place by two small screws. Once it is out of the way the last nut is pretty easy to get to. Plan on leaning into the engine alot. It wasnt that hard for me as I had read in other postings. Some mentioned drilling this one out from the inside of the car. I didnt see it was necessary.
Once all four nuts are removed , its time to go to the inside of the car. Dont get over anxious and try to push the bolt studs through the firewall at this point. There is still stuff inside of the car that has to be moved out of the way.
This stuff is really straight forward to this point. The hardest part I encountered was removing the heater hoses from the throats of the old heater core that I mashed
up. Again, keep this in mind, its leading to something.
Inside, you will have to remove the dash cover. Dont forget the screws from inside of the glove box holding it down. Go ahead and remove the center vents that sit on top of the a/c control panel/box. Remove the large air duct hose that connects from this vent to the upper passenger vent. You will need this duct/hose out of the way to work. Also reach down below where the top center vent connected to the plastic junction that it sat inside of and remove it too. It kind of has to be wiggled and coaxed out.
Go ahead and remove the small duct/hose that runs from the pasenger side lower air vent to the lower center duct juntion/connection that feeds the lower air vent to the drivers side. This junction is kind of box shaped and is pretty much dead center of the dash and mounted on the bottom near the transmission hump. By the way, I call these lower vents that blow the air up the "mini skirt" vents.
Remove the mini skirt vent on the passengers side as well. You will need these extra couple of inches when you get the heater core housing out. While your down there, remove the duct junction/connection that this mini skirt vent connected to. It will also buy you a couple of inches when the heater core box comes out.
Pulling out these lower peices sounds hard, but its not and its better you do it now than when the heater core housing is blocked by them.
Alright, there are a few 1/4 screws that mount the heater core box to the inside passengers side of the firewall. These are a couple of screws that go along the lip of the heater core housing. While your removing these, You will be able to see the round heads of the bolts that you removed the nuts from the engine side of the firewall.
You will see a cable that attaches to one of the diverter doors. It runs along the top left side of the heater core box. Unscrew this as it goes through the heater core housing lip and to the firewall too. Go ahead and remove the end of the cable from the post it connects to. It will allow you just a little bit more room to play around with when you pull the heater core box.
Ok, If Ive remembered everything right, Its time to pull the heater core housing from the firewall. Sounds really easy right? Ok remember the heater core throats that are still hanging from the inside of the firewall? The ones that I hacked up and bent up beyond recognition? Yeah, those guys. I thought I was now at the point were every attaching screw and bolt was removed. I pulled and tugged. The housing would not come off. It was getting hung up on that very first nut that I removed from the inside part of the firewall. Remember the one next to the beat up throats? WELL, I thought that maybe the threaded portion was hung up in the firewall. I knocked on the threaded side where the nut had been a few times hoping to knock it loose. No luck. I crawled under the dash and pulled on the housing some more. Scratched my head a couple of times. I came to realize that those now beat up heater core throats that I showed no mercy on were paying me back. Since they were so distorted, they wouldnt pull back through the holes in the firewall like they were supposed to. They got their revenge, I lost about 30 minutes on that one.
After that, the heater core box came right down. Be sure to lay a towel on the floor before you drop it down. I had a couple of droplets was all.
I started to remove the metal plate from the back of the heater core box to get to the heater core. You will need a shop lamp and a mirror. I dont think Ive gotten them all yet as I cant remove this plate to get to the old heater core.
Im going to look up a few more threads for some insight. Those clips that are square with the round flat heads, the four that attach it to the firewall seem to be part of the problem. Havent figured out how to get them off yet. That and it dropped into the low 30s and I lost my motivation pretty darn quick at that point. Brrrrrrr.
Anyways, I will write again tomorrow as Im getting finished up with it. Sorry, I didnt add any pictures. I couldnt get any decent shots, though I tried.
If any of you reading this can help me out, Id appreciate it greatly! Any of you think this was of use, let me know. Im new here and would like the feedback. Sorry about being long winded, I just dont like looking stuff up on post for advice and getting one liner answers.