C3 70 Headlight Bucket Pop-Up at Speed - NCRS Discussion Boards

C3 70 Headlight Bucket Pop-Up at Speed

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  • Jephrey S.
    Expired
    • April 30, 2000
    • 64

    C3 70 Headlight Bucket Pop-Up at Speed

    Today I am driving my 70 LT1 coupe home from work, most of the time between 80 and 110 mph with no issues. (I think that I have mentioned that I love living in Germany.) Traffic cleared and I sprinted up to 130 mph, glanced down to check the tach (5500), and as my scan went back to waaay in front of me, I noticed something weird. I stopped accelerating and glanced down again to be sure, and verified that my LH headlight bucket was up. I reached over and slapped the headlight switch and verified that it was in the off position. I glanced at the wiper door and it was full closed. At this point I decided that the speed of heat was not the proper environment for troubleshooting and slowed down to 100 mph. I never consciously saw the RH headlight bucket in the up position. As I slowed down, the headlight bucket closed. Traffic was still clear when I slowed down to exit the Autobahn, so I grabbed third gear and ran it back to 5500 rpm to see if it was vacuum related but the headlight bucket stayed down. I got into my driveway and ran the headlights and wiper door through their paces at idle and everything worked properly. Both headlight buckets are faired properly to the nose, with no edges protruding to catch any extra air.

    So, what just happened?
  • Michael W.
    Expired
    • April 1, 1997
    • 4290

    #2
    Re: C3 70 Headlight Bucket Pop-Up at Speed

    It's not that rare to see the headlights doing the opposite of what they have been commended to do while under very low vacuum situations- like WOT at sustained high speed. More owners would see the same condition on this side of the pond if were allowed to drive at Autobahn speeds.

    You have a significant leak somewhere in the system, time to start troubleshooting. There's guides available on line.

    Comment

    • Jack H.
      Extremely Frequent Poster
      • April 1, 1990
      • 9906

      #3
      Re: C3 70 Headlight Bucket Pop-Up at Speed

      The vacuum system is actually TWO systems in parallel. One side is known as the 'servo', it runs off vac stored in the vacuum reservoir and is the side of the system that does physical work (open this, close that). The other side of the system is known as the 'control' system. These hoses are typically smaller in diameter and their job is to tell the servo components WHEN to do their 'thing'.

      Both sides of the vac system derive their energy from the intake manifold. Vac routes from the intake, through a filter, then to a check valve (one input two output nipples). It's at the check valve that servo and control systems separate.

      There is no vac reservoir to 'buffer' vacuum on the control side of the system. The cleanliness of the vac filter (was supposed to be changed out periodically and almost nobody ever changes their filter) and the integrity of the check valve primarily dictate initial vac pressure for the control side of the system.

      The check valve 'buffers' normal vacuum fluxuations on the control side of the system by closing during brief situations where engine vac pressure normally drops (heavy acceleration, Etc.).

      The truth table for the system's control side is: vent vac to actuate the device(s). That means leak(s) or other low pressure episodes can trigger the servo side to actuate this/that item.

      Your RH headlight is the most vunerable of the various Control side items. It's the furthest from the source of vacuum AND it shares its servo side vacuum supply with the wiper door actuator.

      My 'guess' is you have a system maintenace issue and under 'just right' conditions you're seeing false triggering episode(s) of the headlight door(s).

      I'd start by doing the easy chores:

      (1) Have you replaced the system filter with a fresh clean one to maximize vac air flow?

      (2) Is your system check valve in good repair such that BOTH of the umbrella valves in it (one big outlet nipple serving the Servo side and one small outlet nipple for the Control side) are opening and closing FULLY as they were designed to?

      If that's not the source of your problem(s), then it's a matter of troubleshooting the vac system one component at a time from the source of vac to the destination(s) looking for full/partial leaks and fixing them as you go...
      Last edited by Jack H.; August 14, 2009, 12:16 PM.

      Comment

      • Steven B.
        Extremely Frequent Poster
        • June 30, 1982
        • 3989

        #4
        Re: C3 70 Headlight Bucket Pop-Up at Speed

        Supporting Mike's and Jack's comments in the mid '70's I had a friend who used to autocross and road course his '69 small block. It did a similiar thing. You could tell if he was on or off the throttle as his light bucket would go up, then down as vacuum changed. He had a small hose leak in the system.

        Steve

        Comment

        • Jephrey S.
          Expired
          • April 30, 2000
          • 64

          #5
          Re: C3 70 Headlight Bucket Pop-Up at Speed

          Very good explanations, thank you. I have noticed that the headlights do not move as quickly as they used to. This also points to a small leak somewhere. I was also unaware that there is a filter in the system. I will dig out my old vacuum diagram and get this figured out.

          Comment

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

            #6
            Re: C3 70 Headlight Bucket Pop-Up at Speed

            I have had the right headlight on my 70 come up on its own when I am getting on it holding reaching a high RPM in second gear to keep it from shifting to third in my turbo 400 when getting on the interstate from a on ramp. Under normal driving it stays down. I have changed my filter and check valve, but it has been awhile since this was done.

            Comment

            • Jack H.
              Extremely Frequent Poster
              • April 1, 1990
              • 9906

              #7
              Re: C3 70 Headlight Bucket Pop-Up at Speed

              The 'typical' cause for 'dancing' wiper door and/or 'winking' headlight door symptoms is a loss of vac on the control side of the system serving those components. Since the control side of the vac system is NOT buffered by the vac reservoir (storage can ONLY serves the servo side of the system), the typical culprits are:

              (1) Clogged vac system filter.

              (2) Faulty vac check valve (umbrella valve not closing fully on control side; small outlet nipple).

              (3) One or more small leaks in the control system's vac 'pipeline' OR at the controlled vac device itself.

              Comment

              • Jephrey S.
                Expired
                • April 30, 2000
                • 64

                #8
                Re: C3 70 Headlight Bucket Pop-Up at Speed

                It was another Corvette worthy day today (83 deg high, 0% rain chance) so I rolled The Beast out for work again. This morning there was too much traffic to do anything, but I found room to troubleshoot this evening. I have confirmed that it is the LH headlight bucket only that comes up. The RH headlight and wiper door both stay planted. I was able to induce the movement at a sustained rpm of 4800 today (water temp roughly 205 deg F, after 3-5 minutes sustained at speed) and could induce it to happen instantly at will above 5300 rpm. At least I have significantly narrowed the number of places to look for the leak.

                I am glad that both headlights don't come up at speed/low vacuum. I can see myself blowing my Irreplaceable engine while amusing myself winking the headlights at the Porsches, Audis and BMW's with the throttle.
                Regardless, it might be time to seriously think about a crate motor until I get back home.

                Comment

                • Michael W.
                  Expired
                  • April 1, 1997
                  • 4290

                  #9
                  Re: C3 70 Headlight Bucket Pop-Up at Speed

                  Originally posted by Jephrey South (34001)
                  At least I have significantly narrowed the number of places to look for the leak.
                  Not necessarily true. The leak could be anywhere in the system- the RESULT of the leak (an unbalance on the control side) is showing itself first at one headlight bucket.

                  Here's a good troubleshooting guide showing how to test each component:

                  Comment

                  • Edward J.
                    Extremely Frequent Poster
                    • September 15, 2008
                    • 6942

                    #10
                    Re: C3 70 Headlight Bucket Pop-Up at Speed

                    Jack, I Have One Of Those Winking Wiper Doors , When The Car Is Started, The Door Cylces Partly Open And Then Down, There Are No Other Issues, Ive Have A Smoke Machine The Emmits Smoke Into The Vaccum System Could Not Find Any Leaks. Whats The Doctor Rec.(also New Filter And Tryed Check Valve)this Is One Of The Problems I Need To Address Before I Go For Top Flite Next Year.
                    New England chapter member, 63 Convert. 327/340- Chapter/Regional/national Top Flight, 72 coupe- chapter and regional Top Flight.

                    Comment

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