How To: R&R Heater Core in 71-74 Buick, Fullsize

Discussion in 'A boatload of fun' started by GoldBoattail455, Jul 27, 2010.

  1. wixom61

    wixom61 Well-Known Member

    Thank you so much, Rob, for posting these step-by-step instructions on how to change the heater core in a full-size GM.

    I need to do this on my wagon, and also on my '71 Olds Ninety-Eight. I have been totally dreading this job.

    Thanks to your guide, it should go so much easier. And both of my cars just have the manual A/C, so better still.

    I am very appreciative of your efforts. :TU:

    David :)
  2. bammax

    bammax Well-Known Member

    I'm planning on tackling this job in the coming weeks so this thread is a life saver. One question though, is there any way to do this without completely removing all the ducts and the dash pad? I'd rather just disconnect stuff from the box and yank it out without having to do such a meticulous teardown of everything. It's not a resto car so as long as the defog and floor vents work I'm happy.
  3. GoldBoattail455

    GoldBoattail455 462 -> TH400 -> Posi

    I think you would have more difficulty removing the HVAC box that the heater core sits in without removing the ducts or dash pad. This is just one of those cars. It isn't difficult work, just takes some time.
  4. Smartin

    Smartin Staff Member

    I never removed the dash pan in my 71. It remember removing the glove box, but that's about it...maybe some ducting..

    It took me about 3 hours in the driveway when it was a balmy 25 degrees:laugh:
  5. bammax

    bammax Well-Known Member

    I just did this yesterday. It took about 1-1/2 hours because I couldn't get the defroster duct to line up with the hvac box on reassembly. I'll post my differences from what's described here since my car had the standard style heater controls.

    skipped step 1

    skipped step 2

    on 6 I pushed the liner through the back of the dash and pulled it out from below.

    on 7 I lost a screw during reassembly :Dou:

    skipped steps 13-17 since I don't have auto climate control (step 14 came with the hvac box removed and was a mess) I'll list my steps later

    on 19 there are 2 bolts. I don't think you mentioned the one that's to the right and slightly above the one in the pic (it's obvious while you're down there so I doubt anyone would miss it) I did step 19 much later though

    did step 21 same time as step 18 while I was pulling the ducting out

    skipped 22 since I didn't remove the dash

    on 20 there are 2 nuts. 1 being on top and obvious (in your pic) and the other being about 2' unerneath that one and hidden (I found out when I put everything together and found the nut laying under the car. That's why there was some resistance when pulling the hvac box) I did step 20 much later though

    skipped 24-27

    on 28 my car didn't have any grommets :Do No:

    on cars with standard controls there is a cable mounted to the top of the box by a small screw. It's easily visible once the hvac box is dropped down since there is a red square clip that the bolt goes through. The end of the cable is coiled and sits on a stud on the vent door control lever (looks like the throttle lever on a carb but laying down flat) This cable will prevent you from moving the hvac box too far from the dash so you can't really forget it.

    Also there are 4 vacuum lines that are only accesible once the hvac unit is lowed from the dash. They are all on the drivers side and are on the backside of the hvac unit near the dash. I'm going to guestimate the colors as mine are a bit faded. Green/yellow stripe goes to bottom control valve near the center of the hvac unit. Pink stripe goes to top control valve just above the lower valve. Then there are a pair taped together that go to a valve located behind the stereo (up high on the drivers side of the hvac box). These 2 are spererate from the others and both attach to the same valve. All 4 lines have to be removed to pull the box out.

    If you tip the box with the heater outlets pointing down, the entire unit will come out from underneath the dash, but it may mess up your carpet as it could drag the outlets and may dump residual coolant. My coolant level was very low and I was carefull so it didn't show any signs of damage to the carpet (blue plush would show any damage or puddles very easily and mine was fine)

    Now for those who like cliff notes

    Here's my order for the removal process

    19 (2 bolts)
    ** remove heater hoses
    23 (4 nuts)
    ** remove screw holding cable control to hvac box
    ** remove 4 vacuum lines from hvac box
    ** rotate hvac box forward (outlets pointing down) and remove from under dash
    29 (use deep socket and extension on top screw to make it easier)

    Quick note for an easier install:

    *when you put the hvac box back in don't install the nuts or bolts from steps 19 and 23 until after you do step 21 (defrost duct to hvac box screw). If you bolt it all down first than the screw in step 21 will not line up right no matter how much you swear at it.
  6. Yardley

    Yardley Club Jackass

    YIKES!! Briz is right. Mine is a slam-dunk. The shop manual shows having to remove the fender et. al. But the design was changed after the manual was written and the designers cut the heater box into halves. The half with the core just unbolts from the firewall and the core is inside. Just a few minutes.
  7. SteeveeDee

    SteeveeDee Orange Acres

    You big car guys be lucky! My heater core replacement looks like this:

    1. Remove the hood.
    2. Remove the battery.
    3. Remove the right side fender.
    4. Remove the inner fender.
    5. Remove the heater box nuts/bolts.
    6. Weasel that @#$%^&* heater core out of the firewall.
    7. Go to the parts store and order a new core...and find out that the new one has 2 less rows, and doesn't cover the hole in the box, so it allows air leaks, and don't buy it.
    8. Go to another parts store that has a heater core that DOES cover the hole...
    9. Only to find that it's made in CHINEE, and it's aluminum, not brass.
    10. Take it home and put it in...but you'll have to bend the snot out of the inlet and outlet tubes, and cut the firewall, because those tubes aren't even close to the original.:rant:

    11. Try to figure why you're losing coolant 3 months later, then realize that the snot you bent wasn't enough, that the inlet tube is chafing on the firewall, and you're going to have to fix the core yourself.

    At least, that's where I'm at, now. When I DO pull it, for all I know it'll have been defective from the get-go, not a chafe like I'm thinking. I always blame myself first when something goes wrong.
  8. bammax

    bammax Well-Known Member

    I'll tell you where us "big car" guys are really lucky. I did the heater core without having to pull out the passenger side seat. That was a first.
  9. Sergeant Major

    Sergeant Major Biggest Nut in the Can

    It's even easier for us guys with the full size when they are older ... all I have to do is take off my tissue dispenser to get at it. That's gonna happen today. My heater core decided to call it a day (this is the second one). I'm just going to connect the two hoses together, pull out the core (not going to replace it), and call it a day. :Brow:

    Great thread though!!
  10. 73 Centurion

    73 Centurion Well-Known Member


    That's a great write up. Sometimes a thread like this is ideal for deciding whether to tackle a project or not.

    A couple of comments from the "for dummies" perspective.

    Remove the radiator cap when you disconnect the battery to de-pressurize the system.

    Have a plan for supporting the heater hoses when you disconnect them so they don't drool antifreeze all over. A spring clamp and some string work fine. Plan B is to drain the hoses into a container (just be sure to put fresh anti-freeze in when you're done).

    You're write up doesn't mention disconnecting the heater hoses, but I think anyone who can't figure that out probably shouldn't try a project like this.

    Some plastic taped to the firewall below the heater core can catch spills. If you're heater core is leaking you can expect some fluid inside the housing so have plastic in place and paper towels handy.

    Removing the dash pad is not very difficult (particularly after you've done it once). The access you have when it is removed is phenomenal. It's a great time to replace your flexible ducts, check the wiring and even replace a few burned out bulbs.

    Depending on how they are routed the heater hoses can be the highest point in the cooling system. Expect some trapped air to make it to the radiator after you've driven the car for a while.

    You can pressurize the system after the new core is installed and the hoses are reattached. You can do this before everything is completely reassembled. Not every core is water tight from the factory. It's best to know this before you put it all back together.

    It's easy to underestimate how much time and thought it takes to photograph the process as you work. It's also a lot of work to write it up and organize the steps in a logical order while alerting people about to places where their car maybe different. This is a well done thread and it's a great addition to our knowledge base.

    Thanks for the work!

  11. GoldBoattail455

    GoldBoattail455 462 -> TH400 -> Posi

    Thanks guys! It means a lot! :beers2: :TU:

    I have a few more How-To write ups in progress. :Brow:
  12. bammax

    bammax Well-Known Member

    Keep em coming. I read this write up about 9 times before I worked up the nerve to try it. I ended up looking at everything in the car and then looking at these pics one more time before I realized it wasn't so bad.
  13. myriviera

    myriviera Well-Known Member

    Doing my heater core this weekend any suggestions.....73 Riv
  14. magic marouke

    magic marouke Well-Known Member

    really good detailed tear down . ill certainly be referring to this in the next few days as im replacing
    mine . dreading taking the dash pad off as my interior is really nice and dont want to mess anything up
    Last edited: Jan 2, 2018
  15. 66electrafied

    66electrafied Just tossing in my nickel's worth

    The best and only advice I can give is don't force anything. If it doesn't lift off fairly easily then you've left a screw in somewhere. The glove box is the usual culprit as is the ashtray area. Make sure both front doors are open, and be careful of breaking off any of the clips on the area where it clips under the windshield. You may also have to slightly arc it in the centre to get it out if it jams up, but be incredibly careful as if you bend it too much it'll dissolve.
    Leave yourself lots of time and try and stay away from the beer until after the job is done.
    Lucy Fair and magic marouke like this.
  16. magic marouke

    magic marouke Well-Known Member

    I was hoping to start on the beer to help me haha . I’m all about taking my time on stuff like this . They are all different though . My 02 Cummins took over 5 hours and my 70 nova was 45 mins . Well see
  17. magic marouke

    magic marouke Well-Known Member

    changed mine out yesterday at work to take advantage of a heated shop with plenty of room to open both doors . it really wasn't that bad . defiantly agree with taking the dash pad off for more room . it came of a lot easier than I thought it would .


    also taking this bracket above the heater box gave me more wriggle room



    I did cheat on the defroster duct by just bending the two passenger side tabs and zip tying it away enough to pull the box out . can only imagine how hard it would have been to get the far left one . only down side was that I couldn't clean it out .


    had to remove the cable on top of the box which was a little tricky but had to come off to get the box out . took a pic installed to make sure it went back on correctly as there is adjustment slots .


    all in all though it went smoothly . the info in this thread defiantly helped and kept checking back on the pics each step I took . im no mechanic by any means and this is my third heater core replacement and feel confident to do it again . thanks again to GoldBoattail455 for the thread .





    think I found out why it must have leaked . when I removed the hose from the core to by pass it , it was really hard to get off the 3/4 fitting . someone had put a 5/8 hose on there instead and must have forced it on there weakening the solder between the fitting and the top of the core . as you can see the leak is coming from the 3/4 fitting side .
    Last edited: Jan 23, 2018
  18. 66electrafied

    66electrafied Just tossing in my nickel's worth

    Good to hear it went smoothly!
  19. EdwardBryan

    EdwardBryan New Member

    I am stuck at this part. Need help please !
  20. Gordo305

    Gordo305 Member

    How do we take off the A/C evaporator box?

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