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29 special coupe top balloons up

Discussion in 'The Hokey Ass Message Board' started by BillyBobsSpeedShop, Sep 20, 2013.

  1. BillyBobsSpeedShop
    Joined: Jan 6, 2008
    Posts: 522


    So I had the top installed on my 29 special coupe by known local installer. I did look at a 30 sport coupe he did for another guy and it turned out great. My special coupe back window area was changed by adding a 29 regular coupe back window Sheetmetal piece. So when I get up to speed the top balloons up right on top of the car where there is no Sheetmetal? I do not have a headliner in it yet. But with the windows rolled up the top still balloons. I plan on getting the headliner put in soon but not sure if this would help the problem. Can some one give advice? I don't want to drive my car around do to being afraid the material will stretch or tare.

  2. BillyBobsSpeedShop
    Joined: Jan 6, 2008
    Posts: 522


    Bumb any ideas or suggestions
  3. Hot Rod Nut
    Joined: Jul 1, 2006
    Posts: 558

    Hot Rod Nut

    The head liner will help a lot. but getting the top tight first , helps.
  4. jan bogert
    Joined: Jul 11, 2011
    Posts: 655

    jan bogert

    Hotrod is right. I did my own top on my avitar'31 the headliner will help a lot, but it sounds like the top isn't stretched tight enough. you can check it by pushing down in the center with your finger at about a 1/4" you should feel resistence like its tight. if not i'd take it back and tell them. after all u paid money, and its not right. the air underneath the top when your driving is going to pull on the top where the tacks are and start to stretch and elongagate the tack holes, until its very loose, and ugly looking. JMO. JAN.:)

  5. brokenspoke
    Joined: Jul 26, 2005
    Posts: 2,922


    Door windows up or down when this happens?
  6. alchemy
    Joined: Sep 27, 2002
    Posts: 17,251


    Anybody who's followed an old car with a fabric insert will recognize what's happening. It is common. Not saying it should happen though. Ask the upholsterer if he can fix it. It will probably require a whole new piece of material, so he won't offer willingly.
  7. I've seen many old cars do that,my 32 sedan does it but I don't have a headliner,,If it's tight don't worry about it.

    If it's done over the original type chicken wire,batting and vinyl nothing is glued so basically the vinyl is stretched and tacked or nailed.

    A lot of guys today use a thin lauan and glue the materials down so the balloon top is eliminated. HRP
  8. I've owned 5 different convertibles, and looked at every one I see on the road &
    They all do it.

    It's the exact same principle that lets airplanes fly. The rapidly moving air over the top curvature reduces the air pressure on that side.

    Cut a piece of substrate to fit the hole nicely, glue the fabric to the substrate of your choice & then install the cover.
  9. BillyBobsSpeedShop
    Joined: Jan 6, 2008
    Posts: 522


    It happens when the windows are all rolled up also. So not sure how the wind is getting under it?
  10. jan bogert
    Joined: Jul 11, 2011
    Posts: 655

    jan bogert

    you can push the hideum up and run a fine bead of black silicone then push the hideum back down in place. but when the hideum is up and you run the bead make sure that you tool it in to make the seal against the body and the hideum, then push it back in place down against the body. that's the only way your going to seal it from the air going under. JAN. you can use a piece of popcicle stick or thin flat screwdriver to tool it.
  11. The air is sucking it up from the outside not pushing it up from under.
  12. 1971BB427
    Joined: Mar 6, 2010
    Posts: 7,041

    from Oregon

    Are all your doors weatherstripped, and the cab sealed well? I'd guess there's an air leak around the doors or firewall if it does it with the windows rolled up.
  13. motoandy
    Joined: Sep 19, 2007
    Posts: 3,327

    from MB, SC

    Might come in through the visor header area.
  14. black 62
    Joined: Jul 12, 2012
    Posts: 1,895

    black 62
    from arkansas

    neutralize the pressure by cracking the windows a little---been driving convertibles for 50 years , has always worked...
  15. Christom
    Joined: Nov 3, 2011
    Posts: 217


    Like pdunn10 said - It's not wind coming in and pushing it up exactly. When the air is moving over the outside of the top there is no air pressure pressing down on the top from the outside. But inside the car where the air is still there is full atmospheric pressure straight up against the underside - thus ballooning it up. Anyway enough science!
    So having seen this happen on many other old cars I decided that some think-tank time was required before making my insert. :rolleyes: This is what I did......
    I put a non-stretch canvas (stayfast) liner over the ribs. This also formed the nice black headliner (above the exposed ribs) and puts a layer inside the car under the top. This was stretched and tacked down around the perimeter and across all the rib tops. Then a layer of 3mm reinforced sponge mat also tacked down the same way. This also protected the stayfast from the spray-on glue that holds the poly-batting in place. Then more spray glue on top of that and then the proper grainy top material laid out and fixed in the usual stretch 'n tack manner complete with hidem etc.
    The combination of inner layers tacked down on the ribs taking all the internal air pressure and the glued down padding and top holding it all down has really worked out well. No ballooning even with the front window open - but still soft and tight. :)

    Hope this helps....
  16. Back in the late 60s one of the mags road tested a pair of hemi roadrunners. Hard top was several mph faster on top end, at speed the convertible top was ballooning 2".
    The luan idea is the solution to your problem.
  17. Picture is worth 1000 words

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