'68 Vacuum Problems - NCRS Discussion Boards

'68 Vacuum Problems

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  • William S.
    Expired
    • August 31, 1999
    • 39

    '68 Vacuum Problems

    I'm trying to sort out the connections on the various vacuum lines for my recently acquired '68 427 with automatic transmission and power brakes. The correct components are present, and appear as new. I have had the headlight doors and the windshield wiper door both open and close under vacuum control, so I know that the actuators are o.k. mechanically. But I can't get them to operate properly. Does anyone have definitive answers for the following ?
    1. I have used the 1968 Corvette Assembly Manual (pages H249, H255, and H260) as a reference. Are there any known errors or updates to these pages ?
    2. I have verified the proper connection of the "green stripe" and "red stripe" hoses at both the windshield wiper relay & actuator and at the headlight relay & actuator. The "yellow stripe" hose starts at a middle connection of the windshield wiper relay and ends at a middle connection of the headlight relay. What exactly are its connections in between these two points ?
    3. What are the subsequent connections & routing (excluding power brake and transmission) of the hose that starts at the manifold vacuum outlet ?
    4. The tachometer mounted valve shows two hose connections. Is the third, open end of this valve supposed to be closed off ? If so, what is the factory method for doing this ? Also, are there supposed to be any electrical connections to this valve ?
    5. The windshield wipers will move to the park positon on their own, but don't seem too interested in actually going back and forth over the windshield. Could vacuum problems be causing this ?
    6. My car is missing many of the "existing clips" shown in the Assembly Manual as securing the vacuum hoses onto the fenders within the engine compartment. Are these clips reproduced, and if so, who sells them ? How do these clips attach to the fender ?
    7. I notice that the driver's side headlight door opens/closes slower than the passenger side headlight door. My son notices the same phenomenon on his low mileage '82 Collector's Edition. Is there a reason for this, or is it only coincidence ?

    Thanks in advance for any help that anyone can provide.
  • Jack H.
    Extremely Frequent Poster
    • April 1, 1990
    • 9906

    #2
    Re: '68 Vacuum Problems

    There's too many questions here to 'walk' you through diagnostic/repair... I suggest you purchase one the vacuum troubleshooting books (Dr. Rebuild, Mid America, Etc.) to read and get to understand how the system works and, in general, how you go trouble shoot it. You'll find past threads on various specific subjects in the archives plus a copy of the 1968 Chevrolet Chassis Service Manual talks specifically about how the various subsystems work. But, a couple of comments.

    (1) The wiper is an electro-mechanical system. Vac is used to open and close the wiper door. An electrical limit switch senses when the door is open and relay's electrical power to the wiper motor (no sense is starting the motor if the wiper door isn't up/open!

    (2) The electro-vac relay on the back of the tach, either passes vac to the other wiper door contros (the over-ride switch beneath the steering column) or opens and vents vac to cause the wiper door to open when the wiper switch is turned on. There are only two vac connections to the relay and the third nipple serves as a vac vent port.

    (3) Your car is different than your son's '82. The later car has no wiper door. The way your car's vac 'plumbing' is routed, the wiper door and the RH headlight share the same vac servo line. So, minor leaks in the wiper door 'plumbing' will affect operation of the RH headlight! In the case of your son's '82, there is no parallel sub-system running off the RH headlight.

    When all is correctly routed and leak free, expect both headlights to JUMP open almost in unison and shut the same way...

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