Engine Going Dead With Breaks Applied

Discussion in '40- & 55-Series Tech' started by blueticker17, Aug 16, 2006.

  1. blueticker17

    blueticker17

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    My engine is dying when I apply the breaks. It goes slowly. When it is cold or warm. It does not matter how hard i press them (ie slamming on).

    I have a 79 40 with a weber carb. No other engine mods.

    I have no electrical probelms (right this minute). Batts are fully charged. The breaks are fairly new and in good service. It has only recently been doing this and has only been happening since it has gotten hot.

    Please help I feel like a douce having to restart after every stop light/sign.:doh:
     
  2. Poser

    Poser Oh...Durka Durka Durka. s-Moderator Supporting Vendor

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    Bad brake booster....
     
  3. Trollhole

    Trollhole THC Supporting Vendor Moderator

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    what he said.
     
  4. Fast Eddy

    Fast Eddy

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    x3 Same thing happened to me. After fixing all the other brake parts, some twice, it was heartbreaking.

    Oh, and it's "brakes", as in, "Doesn't it suck when your brakes break?"
     
  5. 1973Guppie

    1973Guppie Supporting Vendor SILVER Star

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    just for curiousity's sake, what causes this exactly with the brake booster being bad? just interested in learning what happens and why....

    Noah
     
  6. Pin_Head

    Pin_Head

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    Massive manifold vacuum leak, so it will only die when idling but not at higher RPM.
     
  7. CruisinGA

    CruisinGA

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    Brake boosters use a large rubber diaphragm and engine vacuum to "boost" the pressure you apply through the pedal. When that diaphragm goes bad, you not only loose the effectiveness of the booster but it introduces a vacuum leak into the intake. Instead of the engine vacuum just pulling on the diaphragm, it pulls outside air into the intake.

    The only thing different about this vacuum leak than any others is that because of the location of the brake booster hose on the intake manifold, only cylinders 5 and 6 see a seriously lean condition from this leak, and hence you often see old engines with cooked valves or other lean-condition problems on cylinders 5&6.

    There you go, more than you cared to know about leaky brake boosters.
    :cheers:
     
  8. bsevans

    bsevans Focus on the Journey

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    What caused my booster to fail was the brake master cylinder rear seal. It failed and leaked brake fluid into the booster which eventually caused the seals in the booster to fail. I removed the four nuts holding the master cylinder to the booster and just pulled the MC forward without removing the brake lines, the leakage into the booster was quite obvious.
     
  9. Fast Eddy

    Fast Eddy

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    Mine only leaked when I pressed on the brakes. It would idle fine otherwise.
     
  10. Pin_Head

    Pin_Head

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    Yes, as noted in the first post, it only dies when the booster leak is activated by stepping on the brake pedal.

    My point was that if you stepped on the brakes and revved the engine at the same time it wouldn't die because the manifold leak isn't as big of a problem with the throttle open. It will only die if it is idling and the leak is activated.
     
  11. Doug_S

    Doug_S

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    If it dies at all RPM's then look for an electrical problem (short in the system between the brake light and ground). If, on the other hand, it only dies at idle I'd second the thought of PinHead.

    Good luck!
     
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