A-Body Heater Core Replacement
 

Ahh, yes - you guessed it: the dreaded chore of replacing a 50 year old part that's buried in the car.

I'm about halfway through it (definitely had to walk away a couple times) and have that elusive firewall bolt left to remove, as well as the heater cables and ultimately the box/core.

I have all the hardware I'll need to reinstall, along with a re-cored Harrison unit. What I would like to not have to do is drop the inner fender and I'm definitely NOT drilling any holes in the car to access that nut.

That said, do you A-Body guys have any tips to pass along? I'm going to try and get most of this finished up tomorrow afternoon.

Thanks in advance!

Not aware of any other way but drilling out the offending stud from the inside of the passenger compartment. Maybe others know something different?

Assuming you are talking a 68-72 A-body or your Buick, all you have are the two bolts left, leave them! The two bolts at the blower motor end will retain the engine side housing in its original position and have nothing to do with the inside box. You only need to remove the 5 nuts on the firewall side. That being said, it can be a little interesting to get the inside box studs and the heater core hose nipples to be reinstalled into the housing when you are done but I have done it. You also do not have to remove the control cables. Simply drop the box and "roll" it on its side so that you can remove the core. I believe your Buick has plastic inner fenders so you may actually be able to twist and remove them but I would not recommend it. If your car has is an AC car (obviously your Buick is not) that is a whole different monster.

If you do feel you need to remove the last two bolts, all you have to do is drop the inner fender down by removing all the attaching bolts as well as the battery tray to inner fender bolts and pull it down enough to get your arm in. Protect the frame with towels between the frame and the inner remaining bolts. I find it easier to remove the blower motor if you are doing that to take some of the weight off but depending on how far you drop the inner fender down you may not be able to remove the motor. I have done this a few times without any damage to the car or the inner fender.

Rick,

Thanks for the reply.

It's actually my '70 Stage 1 and to be honest, I'm a bit overwhelmed. Also, depending on the condition of all the inside stuff, I'd like to clean up the box, seals, etc.

Of course, this requires removing the cables, so....

It is really not as bad as it sounds. I had a customer's car blow a heater core after a show and we had the replacement core removed and reinstalled in less than 2 hours. If you are removing the inside box completely I would simply remove the heater selector with it and leave the cables in tack as to me they are easier to remove out of the car than trying to do it in the car and the selector is not hard to remove with the box (in a Chevelle). The other bad part about removing your firewall side box if you do is that you will disrupt the original undercoating that was sprayed there.

Leaving the whole heater control intact is a good idea. I didn't think of that. I wonder if the Buick set up will pull through to the inside of the dash.

That will make things much easier.

I have never has a Buick in the shop so I cannot comment but just by appearance I believe they are very similar in their removal. Wrap the control in a towel and put a piece of masking tape around it. This will protect it and the dash during removal.

Thanks!

I keep you posted.

I was able to get that nut off and the box out without removing the heater control or drilling any holes.

I used this ratchet with a shorter socket and was able to get it loose. I did the rest by hand with a magnet handy and am confident I'll be able to get it back on.

https://www.amazon.com/dp/B00DSR50BQ..._v5RsDb53324CF

Tonight, I'll clean up the heater box and add new padding to both sides of the door/flap, as well as 3M caulk strips where the core will sit. The heater control is going to get lubed up VERY well, too and should be good for another 50 years.

Also, during reinstall: I think leaving the top of the heater box leaning toward the back of the car (and the cables unscrewed from their respective colored tabs) makes it easier to reapply the cables to their correct mounts. Unscrewing them from the colored tabs also releases tension, limiting the chances of actually breaking the tabs.

Stay tuned....

Forgot to update this.

With a total of probably 10 man hours into this - from start to completion, it was a successful project. Not to mention one of the biggest PITA projects the layperson will probably ever do on one of these cars.

Once I got the heater box out, I scraped all the old caulking/sealant off the edges and applied 3M caulk strip to the cleaned surface.

After that, the rebuilt Harrison core was secured back in and then the box was reinstalled. With a few choice swears, of course.

I was also able to get that ever elusive speed nut back on. The trick is to use a little dab of that 3M caulk strip on your fingers - or the nut - whichever you find easier.

Once you can get that nut to turn - even if it's just a half turn - and you feel like it's "straight" on the stud, use a ratchet head wrench to finish it off.

Voila! No holes drilled and no body panels removed.

If I could post pictures, I'd show a detailed depiction of this whole process.