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Thread: Severed/Crushed Vacuum Tube to Hot Water Control Valve - Effect on system?

  1. #1
    Junior Member JCochrane's Avatar
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    Location:  Milwaukee, WI

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    Question Severed/Crushed Vacuum Tube to Hot Water Control Valve - Effect on system?

    When I had the console off, I found this tube, partially crushed in one place [img1] (maybe when I removed the console), and then noticed it was completely detached at the back end, and quite possible chewed by some mouse at some point. I fished the other end out through the locked compartment behind the driver's seat, and reinforced that suspicion [img2].

    Looking at the head end, I thought maybe it was an aftermarket/replacement piece as it plugs in to a soft rubber tube that connects to the tee, which I think makes it part 29 on 7-3-0 . So I'm obviously ordering a replacement tube. I thought it was maybe supposed to be soft rubber all the way back, as I don't see the same soft-hard junction [img3] on the parts diagram, but then part 29 description says its hard plastic:
    This is the long, hard, black plastic tubing that runs along the side of the center console from the hot water control valve to the tee connector behind the radio which in turn connects to the air inlet valve assembly and the mode control switch.
    Is there a different part for the soft rubber tubing section? I don't think I need it now, but curious. And do I need to order a new grommet too? I haven't tried to fish that out to see if it's ok.

    And since it was clearly damaged for a while, I'm curious if there could be other damage to the system - anything else I should check? Or would it just be a loss of vacuum pressure, either in that one line/component or in the system as a whole?

    I guess I should take the mode switch off and re-build and lube it while it have it all apart...

    20220503_071931.jpg 20220503_072819.jpg 20220503_071910.jpg

  2. #2
    Senior Member Rich's Avatar
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    Location:  San Francisco Bay Area, Calif.

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    About your 3 questions:

    1. Yes, the soft rubber tubing has its own P/N. "Connector" is #106211, showing as NLA at DMCH, Item 5 in this diagram. There is one of them at each end of the hard tube. The one in the engine bay connects the tube to the vacuum diaphragm on the hot water valve behind the intake manifold. You need to use them both, or something similar, along with the replacement hard-tube you're getting in order to make the system work. Try to route the new hard tube so it won't get crushed again, of course.
    2. The grommet, Item 30 in that diagram, is the one the hard tube where it goes through the wall of the left pontoon. The grommet is probably there mostly to keep the hard tube from hitting the body tub as well as locate it left-right to keep things looking OK back there. It's <$2 so I'd put one on.
    3. The crushed hose didn't damage anything. Worst case the crushed part made your hot water valve non-responsive to the mode switch, allowing hot coolant to flow through the heater box when you run in MAX mode. If it was also disconnected in certain spots you'd have an intake vac leak. Again, no damage, only a chance of a mixture/idle issue.

    Quote Originally Posted by JCochrane View Post

    Is there a different part for the soft rubber tubing section? I don't think I need it now, but curious. And do I need to order a new grommet too? I haven't tried to fish that out to see if it's ok.

    And since it was clearly damaged for a while, I'm curious if there could be other damage to the system - anything else I should check? Or would it just be a loss of vacuum pressure, either in that one line/component or in the system as a whole?

    I guess I should take the mode switch off and re-build and lube it while it have it all apart...

    20220503_071931.jpg 20220503_072819.jpg 20220503_071910.jpg
    March '81, 5-speed, black interior

  3. #3
    Senior Member
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    Not much to add but check the hot water valve and make sure it opens and closes. When they don't move for a long time they usually get stuck. The only time it is closed is when you are in the MAX A/C position so you wouldn't notice it. If the mode switch actuates things like it should and doesn't hiss you don't have to touch it.
    David Teitelbaum

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