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Tunnel insulation

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  • Pete G.
    Frequent User
    • October 21, 2008
    • 50

    Tunnel insulation

    When I purchased my '68 L68 back in '05 it came with a silver/reflective type of insulation (about half inch thick) around the bell housing portion of the firewall and extends under the floorboards. Just prior to my purchasing the car it had the engine rebuilt, was this insulation added as aftermarket prior to putting the rebuilt engine back in the car? Or did the factory include this insulation?


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

    #2
    Re: Tunnel insulation

    I'm not real familiar with 68...it is the first year of C3 and different from later models in many respects.

    Later models have a foil covered fiberglass tunnel insulation blanket. IF the insulation IS original to your 68, I would expect it to be retained to the tunnel with four clips that are riveted to the underbody. These clips each have two pointed ears that pierce through the insulation when it's installed (with adhesive), and the "ears" are bent back over the insulation blanket to retain it in position.

    Comment

    • Paul O.
      Frequent User
      • August 31, 1990
      • 1716

      #3
      Re: Tunnel insulation

      Pete the insulation on 68's varied by production date but from your description it sounds to be correct. I do not remember when all the changes occurred off the top of my head. 68's had a lot more insulation then the following years.

      Paul 18046

      Comment

      • Pete G.
        Frequent User
        • October 21, 2008
        • 50

        #4
        Re: Tunnel insulation

        Chuck, Paul, thanks for the info.!

        It seems to me the insulation is not very resilent to the elements (road debris, water, etc)? I've driven my '68 ~ 3K miles over the past 5 years (don't take it out in the rain) and it's looking a bit ragged especially around the floorboard area. And in looking back to when I bought the car in '05 (immediately following engine rebuild in which believe the previous owner replaced the insulation), I cannot think the insulation would stand up to daily driving. Did owners need to change this out on a routine basis?

        Comment

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

          #5
          Re: Tunnel insulation

          Originally posted by Pete Gillie (49588)
          It seems to me the insulation is not very resilent to the elements (road debris, water, etc)? I've driven my '68 ~ 3K miles over the past 5 years (don't take it out in the rain) and it's looking a bit ragged especially around the floorboard area. And in looking back to when I bought the car in '05 (immediately following engine rebuild in which believe the previous owner replaced the insulation), I cannot think the insulation would stand up to daily driving. Did owners need to change this out on a routine basis?
          I suspect the original insulation installed at the factory was higher quality than the typical reproduction, but, by it's nature, none of it was going to very resistant to weathering.

          I seem to recall a side by side comparison I made that showed the original material much denser that the typical repro. I'm pretty sure the original GM material hasn't been available for decades, and like so many replacement parts, you're pretty much stuck with whatever is being offered.

          To answer your question about replacement, you can be pretty sure that GM NEVER intended this insulation blanket to be replaced...only one to a customer. Historically, most people that just drove these cars never even know they were there. GM never considered that 40 years later, people would looking close to see if it was there and what condition it was in. That insulation was expected to serve a function, and if it happened to shread and fall off years later, that was just a part of the natural aging process.

          Comment

          • Michael D.
            Expired
            • June 30, 1996
            • 536

            #6
            Re: Tunnel insulation

            The tranny tunnel blanket is correct. It is also possible your car could have had left and right underbody blankets of the same material running from the footwells to over the toe kick. One way to tell for certain is to look for vestiges of the old insulation or the clips used to hold them on.

            If memory serves, the AIM shows installation of the clips for the underbody blankets but does not show installation of the insulation.

            Comment

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

              #7
              Re: Tunnel insulation

              Originally posted by Michael Davenport (27810)
              ...If memory serves, the AIM shows installation of the clips for the underbody blankets but does not show installation of the insulation...
              If the 68 AIM is organized like the 70 AIM, installation of the tunnel insulation blanket would be very early in UPC 1, Bolt Weld. In the 70 AIM, it's in UPC 1, Sheet B6.

              Comment

              • Dennis S.
                Expired
                • April 1, 2004
                • 228

                #8
                Re: Tunnel insulation

                Pete
                Not sure about your '68, but my April '69 had it all. There were metal floor pans and plastic toe boards to protect the insulation. See post #6 in this thread for pictures of mine, after restoration:

                https://www.forums.ncrs.org/showthre...80613&uid=6438

                Check the '68 AIM for your build date

                Comment

                • Terry M.
                  Beyond Control Poster
                  • September 30, 1980
                  • 15595

                  #9
                  Re: Tunnel insulation

                  There was a 1968 TSB (Technical Service Bulletin) describing how to add the extra under floor boards and associated insulation to 1968 Corvettes. If I am not mistaken it also gives serial numbers for the installation in production.

                  I remember in the early '90s trying to track the installation of that extra insulation on 1969s and all it accomplished was to frustrate Dennis Clark by delaying the "new" manual. He is still frustrated about that as those of you who were at the National Awards presentation in Concord last Summer saw. My best conclusion was that the larder, higher performance engine cars got the extra insulation in 1969, and the lower performance cars did not, but I never got enough solid data points to be comfortable with that conclusion -- so this is the first and last you will hear of that idea.
                  Terry

                  Comment

                  • Jim B.
                    Very Frequent User
                    • July 31, 2002
                    • 146

                    #10
                    Re: Tunnel insulation

                    My original owner 68, Late July 68 car, has the tunnel insulation and all of the floorboard insulation. Over the years it has really made a mess of the undercarrage so it has to be replaced. The foil disintegrates and the fibers string out. I would expect that if it is the original insulation it would sure show its age.
                    Jim Boudreaux
                    LA Chapter, NCRS

                    _____________________________
                    1968 British Green Convertible 327/350HP Original Owner
                    2002 Z06 Black on Black Original Owner
                    2007 Z06 Velocity Yellow w/Black/Titainium Original Owner

                    Comment

                    • Russ S.
                      Extremely Frequent Poster
                      • April 30, 1982
                      • 2162

                      #11
                      Re: Tunnel insulation

                      quote=Terry McManmon (3966);530086]There was a 1968 TSB (Technical Service Bulletin) describing how to add the extra under floor boards and associated insulation to 1968 Corvettes. If I am not mistaken it also gives serial numbers for the installation in production.

                      I remember in the early '90s trying to track the installation of that extra insulation on 1969s and all it accomplished was to frustrate Dennis Clark by delaying the "new" manual. He is still frustrated about that as those of you who were at the National Awards presentation in Concord last Summer saw. My best conclusion was that the larder, higher performance engine cars got the extra insulation in 1969, and the lower performance cars did not, but I never got enough solid data points to be comfortable with that conclusion -- so this is the first and last you will hear of that idea.[/quote]

                      Terry. I am working on a 69 serial number S721110, an original 390 HP and although the insulation is gone the tabs are there for the tunnel insulation as well as the two foot wells. RS

                      Comment

                      • Jeffrey S.
                        Extremely Frequent Poster
                        • May 31, 1988
                        • 1882

                        #12
                        Re: Tunnel insulation

                        My October '68 base engine automatic has all of the above. Although the original insulation on the floor boards was long gone, the clips are all there.
                        Jeff

                        Comment

                        • Lawrence M.
                          Very Frequent User
                          • February 1, 1995
                          • 404

                          #13
                          Re: Tunnel insulation

                          The TSB Terry refers to is number 68-T-43 dated April 22, 1968.
                          Heat Insulation was installed in 2 steps in production starting with rear stowage compartment insulation on serial no. S409315 and secondly the addition of heat insulation pads to the underbody starting with serial no. S409939.
                          Larry
                          2002 Z51 Convertible
                          1969 L46 Convertible

                          Comment

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