C4 heat/AC box replacement - NCRS Discussion Boards

C4 heat/AC box replacement

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • Larry E. Howard

    C4 heat/AC box replacement

    Just bought a 1993 LT1 that has some damage. I am in the process of replacing the complete heater box on the engine side of the firewall. It would appear that to complete the job I need to remove the brace running from the frame to the right hood latch. the 3 bolts on the latch came right out but the two top ones on the frame just spin and do not back out. It would appear that the nuts on the inside of the frame are not welded to the frame. Can anyone offer any help or insight on this problem.
    Thanks Larry
  • Chuck S.
    Expired
    • April 1, 1992
    • 4668

    #2
    Re: C4 heat/AC box replacement

    Larry, the first thing I would do is order a GM service manual. It will probably cost you a couple of hundred bucks, but the OEM manual is indispensible in my opinion. In general, if you do what it says, you won't make mistakes that can really cause you some grief. Sometimes you can find used manuals cheaper on ebay.

    Concerning your diagnosis of the problem, I don't currently own a C4, but I would say that the nuts were welded at one time; if the car took a blow on the right front that destroyed the heater box, that may explain how the "tack" welds were broken Have you checked underneath the frame rail to see if there aren't access holes that allow a socket/extension to be placed on the nut? The nuts had to placed and welded AFTER the frame rail was fabricated.

    Of course, getting the nuts off is only half the problem; I believe I would have a plan for putting them back before I removed them. For example, IF there are access holes, I would convince myself that I could successfully start and tighten the nuts from the bottom using a socket on an extension (and possibly a helper).

    Comment

    • Joe L.
      Beyond Control Poster
      • February 1, 1988
      • 43193

      #3
      Re: C4 heat/AC box replacement

      Larry-----

      Heater box and heater core R&R on a C4 is a challenge, to say the least. As Chuck mentions, you need a GM Service Manual for 1993 Corvettes, if you don't have one. If someone has a 1993 Corvette (or, any year Corvette, for that matter) and they want to perform just about ANY work on their car more than changing the oil, they ABSOLUTELY MUST have the GM Service Manual. If someone has a 1993 Corvette which is damaged and in need of rather extensive repair, then they ABSOLUTELY, POSITIVELY MUST have the GM service manual.
      In Appreciation of John Hinckley

      Comment

      • Jim T.
        Expired
        • March 1, 1993
        • 5351

        #4
        Re: C4 heat/AC box replacement

        Larry the 93 Corvette service manual is still available from www.helminc.com for $90 plus shipping. This is the same place where a dealership or independent shop would buy a new 93 Corvette service manual for their shop. My service manual for my 85 is about 1 1/2 or larger in thicknes and just one volume. My 96 service manual is about 4 inches or more thick and comes in two books, one is just for the engines and transmissions. If you do not have a owners manual for your 93, you can also purchase a new one from Helm.

        Comment

        • Larry E. Howard

          #5
          Re: C4 heat/AC box replacement

          OK guys, Thanks for the input. I know I need a service manual, and I have bids on several on ebay. I really don't think the problem I have with the bolts not backing out will be covered. I was hoping that someone might have some experience with this problem. there is a hole in the frame that I can get a 13mm wrench (the bolt head outside the frame is 13mm) into but can't seem to get hold of anything, the hole is about 2 inches below the top of the frame so the wrench is at quite an angle. A 14mm wrench won't go in the hole. Since I will have to use longer bolts to replace the ones there now, I am considering drilling or grinding off the ones in there now.

          Comment

          • Chuck S.
            Expired
            • April 1, 1992
            • 4668

            #6
            Two Things...

            (1) I presume you are using a straight extension. Try using an extension with a 3/8" drive universal joint on the bottom of a short socket; Sears sells the universals in a set...1/4", 3/8", 1/2". You might even try using a smaller 1/4" drive 13mm socket, but use the break handle and not the rachet...those little 1/4" drive rachets won't take much abuse. It still won't be easy to get the socket on the nut with that universal flopping around, but if this was easy our wives wouldn't need us. BTW, it may be that the old weld material is keeping the socket off the nut...if that's the case, and you having zero success, see (2) below.

            (2) You can cut'em off, but that won't help you put'em back. Better have a plan, and this is where a lot of ingenuity is going to help. If you can't get to the nuts from the bottom (or side), then you will need to secure the nut/bolt shaft some way to keep them from falling into the frame until the support is out of the way. THEN, if you have a welder, you can probably position the nut/shaft properly by feel (realign the broken welds to their original position), and tack weld the nuts to the perimeter of the frame hole from the top. Better take some precautions (chewing gum? painters putty?) to keep weld splatter from welding the shaft into the nut. Then, apply penetrating oil and let it set overnight. Screw the bolt shafts out using vise-grip pliers set such that you can barely get them closed. You'll probably need to grind the welds flat for your support to fit properly, so better get really good penetration or don't grind off too much.

            (3)? IF you think you can get a new fresh nut started from the bottom (side), another option might be to just cut the heads off one at a time, and use a strong magnet to recover the nut/shaft. Then, just replace the bolts with new hardware. Better use a lock washer or lock nut of some type on the inside of the frame. A lock nut will probably be much easier to work with than a separate lock washer (a recipe for insanity), but the disadvantage of a lock nut is that they will have resistance all the way up the shaft. So...don't make the bolt any longer than it needs to be to give you about 1.5-2 nut thicknesses of engagement inside the frame.

            Incidently, the service manual won't cover things like what to do when nuts break loose inside the frame. We mention the manual only to keep you out of trouble in other areas.

            Comment

            • Larry E. Howard

              #7
              Re: Two Things...

              OK I used a mirror to look into the acess hole and found that the nuts are round on the two top bolts and there was a square nut welded on the side for the side bolt. I was able to back the side bolt out. I then drilled out the two top bolts and recovered the nuts from the inside. These appear to be a press fit since I had to knock them out when the head drilled off. there is no sign of a weld!!
              Some day I would like to see the memo that GM sent it's engineers, telling them to use only fine thread bolts in hard to access places and make them an inch longer than they need to be!!
              Replacement should be pretty straight forward like you said. It kinda reminds me of the puzzle a fastener salesman once gave me. You know the one with a pop bottle and some bolts, washers and nuts. and you have to assemble them inside the bottle. It can be done. Just takes patience.

              Comment

              • Chuck S.
                Expired
                • April 1, 1992
                • 4668

                #8
                Re: Two Things...

                Larry, I am pleased that you are making progress.

                Press fit??!! Sometimes you just have to dive into these non-lethal, non-expensive-damage projects and see where it leads you. I suppose the diameter of those round, press-fit "nuts" are larger in diameter than a 13mm hex lock nut across the corners (max diameter)? If a 13mm hex nut won't fit in the "hole" that's left, you may have another problem...it'll be "fender washer" time then. This problem could get nastier.

                Comment

                • John H.
                  Beyond Control Poster
                  • December 1, 1997
                  • 16513

                  #9
                  Re: Two Things...

                  Those were known as "pierce-nuts"; they clinched in place (small collar on one side of the nut). Less costly manufacturing process than weld-nuts, but frequently become "un-clinched" years later when trying to remove a rusty bolt

                  Comment

                  • Larry E. Howard

                    #10
                    the final solution for replacement of brace

                    Rather ingenious if I do say so Myself. I will have a small plate made 4 X 3/4 inches out of 1/8 or 1/4 stock. Will drill 2 holes 3.1 inchs apart center to center. Weld on two 8mm nuts on the 3.1 inch centers. This will easily go in the acess hole. I will then, with the brace in place, run a 3 inch 8mm bolt down and into one of the nuts. once the threads are engaged I can pull the plate up and into place and start the correct 8mm bolt in the other hole. once it is started I can remove the long bolt and install the correct bolt in the last hole. tighten everything and it all appears to be as though nothing ever happened.
                    End of story! Thanks you all for all your input. I will be on the road soon! Larry

                    Comment

                    Working...

                    Debug Information

                    Searching...Please wait.
                    An unexpected error was returned: 'Your submission could not be processed because you have logged in since the previous page was loaded.

                    Please push the back button and reload the previous window.'
                    An unexpected error was returned: 'Your submission could not be processed because the token has expired.

                    Please push the back button and reload the previous window.'
                    An internal error has occurred and the module cannot be displayed.
                    There are no results that meet this criteria.
                    Search Result for "|||"