Brake booster short circuit

Discussion in 'Electrical & Audio' started by Whitelightning, Jul 10, 2018.

  1. Whitelightning

    Whitelightning Junior Member

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    So I have any 86 k2500. I am currently in the process of swapping a 350 to a 400. I got the motor in and bolted up to the frame and tranny. I put the starter on to crank it over a few time to prime the oil system. After about the third time the motor cranked over there was a small section of my brake booster the was red hot. The is no wires inside or out that would be shorting it out that I can see .I have looked under that dash, Ann around the engine bay and I can't come up with anything. I am at a loss. I don't know how to even diagnos this issue. Any help is greatly appreciated. Thanks
     
  2. PrairieDrifter

    PrairieDrifter Full Access Member

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    We need a little bit clearer information. Are you sure the brake booster is what you’re talking about? Not to sound like an ass and not trying to insult your intelligence. Just that the brake system has nothing to do with the engine, much less the booster.
     
  3. T-ROD

    T-ROD Full Access Member

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    Sounds like a ground to me for sure, they can do some wild stuff, have someone hold a multimeter to ground terminal on battery and other to a bracket or intake on motor, and crank for a second or two, if the voltage is real high like 2-3 volts that's way too much loss for a cable, you are probably missing a ground strap or a cable to block, it should be directly to engine block from battery negative, and there should be a stray from bell housing bolt or intake to body and frame, them are the most important ones, other than the obvious, because some higher compression engines can literally take somewhere around 255 amps to crank, try that first, if it's high it's probably using the body parts as a ground, Is it cranking slower than you'd think it should? And is everything else working correctly?
     
  4. chengny

    chengny Full Access Member

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    Something is shorting to ground through the booster. Post an image of where the hotspot occurs.

    Also, try turning the ignition switch just to RUN (don't go to START). Wait a while and see if the same thing happens. The only additional circuit that becomes hot when cranking the engine is the purple wire that runs from the ignition switch to the starter solenoid.
     
    bucket likes this.
  5. Whitelightning

    Whitelightning Junior Member

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    It is cranking very slowly. And in the picture you can see the section just slightly up to the right of the column.

    Snapchat-1412409674.jpg
     
  6. highdesertrange

    highdesertrange Full Access Member

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    I need popcorn for this one.

    I can't see why it would get hot there but are you sure you didn't pinch any wires between the engine and bell housing?

    highdesertranger
     
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  7. 1987 GMC Jimmy

    1987 GMC Jimmy Full Access Member

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    Here you go:

    :popcorn:
     
  8. T-ROD

    T-ROD Full Access Member

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    Ml



    That's true, it could do the same, but the load of the starter to ground would be many times more than that of any ignition or accessory more than likely, it wouldn't get that hot if it did at all, it is real strange that it's in a specific area of the booster and the fact that out of all places it does it there, kinda gets my brain warm
     
  9. T-ROD

    T-ROD Full Access Member

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    The reason I was thinking engine ground is because if you don't have a good ground there, it could feed through brake lines in that particular vicinity through frame and other components and it would make a ground through the master cylinder and brake booster into the firewall
     
  10. smoothandlow84

    smoothandlow84 I'd rather be draggin' frame

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    Something is shorting out.....
     
  11. roundhouse

    roundhouse Full Access Member

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    You have a good ground wire from the battery to the frame ?

    From the frame to the body?

    From the battery to the body ?

    From the battery to the engine block near the starter ?

    All of these should be good quality wire with clean shiny terminal ends and clean shiny bolts and clean shiny pads on the body frame and engine where they bolt down
     

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