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Idle problems after brake booster replacement

Discussion in 'Bay Tech Clinic' started by AvocaBus, Jan 5, 2011.

  1. AvocaBus

    AvocaBus New Member

    Messages:
    4
    Location:
    Avoca Beach, N.S.W
    Hi,
    I am experiencing a problem after a brake booster(used ex1976) and a new master cyclinder has been replaced in our 1971 1600cc bus.
    It will not idle correctly after the booster was replaced. My guess is a vacuum leak?

    To prove this is it reasonable to expect that if the hose coming from the manifold that eventually feeds the booster is blocked thus eliminating a source of a possible leak, the idle should return? Would the carby require any adjustments after a booster replacement?
    Also there are 2 hoses feeding the booster 1 to the reservoir and another to ambient air. The ambient air hose disappears up into the frame below the drivers seat. This hose the mechanic said was full of crud so was removed and cleaned- anything special about that hose?

    Before the work was done there was no idle problems. Hopefully it is something simple I have (and the mechanic) has missed. Any advice would be very much appreciated.

    Cheers,
    Paul
     
  2. oldman

    oldman Super Moderator Staff Member

    Messages:
    8,740
    Location:
    Avalon Beach NSW
    Hey Paul, If blocking the vacuum line from manifold to booster doesn't alter the issue. it's more likely to be a breech in the hose,(hole) OR the one-way valve is either stuffed, or has been placed 180 degrees 'round the wrong way . The valve should have an arrow that points towards the engine/manifold. The one-way valve should be just after the take-off of the manifold - it's quite obvious.
    I'd be checking that the one-way valve is facing the right way first & then replacing the hose with new stuff. The ambient air hose shouldn't be a concern - it just supplies air to the other side of the booster diaphragm.
    If you had holes in the vac. line & the bus has been tuned without fixing the line issue before, it will run differently & will need re-tuning. If the mechanic you went to was a VW bloke - he should have picked up on all of this :wtf:
    If you've replaced the booster with a second hand unit, was that unit tested for vacuum leaks before installation ? If the diaphragm is buggered you'll get the same effect as a stuffed vacuum hose.
    I've done this replacement - booster - on a '71 lowy & heeding good advice, replaced all the hoses at the same time. It fixed the rough idle issues that we had at the time, as well as giving us our brakes back !!
    If your booster is stuffed, flick me a pm. I'll give you the name of a place that can supply new units for around $250.00. Cheers, Mark
     
    Last edited: Jan 5, 2011
  3. AvocaBus

    AvocaBus New Member

    Messages:
    4
    Location:
    Avoca Beach, N.S.W
    Thanks Mark,
    Seems as though all is well. After a nights sleep and some thought it occured to me that the bus was probably tuned with a vacuum leak from inside the booster. A simple carby adjustment and my idle has returned. I would have assumed the mechanic would have worked that one out and not just because "the engine is cold" despite it actually was hot.
    Cheers, paul
     
  4. oldman

    oldman Super Moderator Staff Member

    Messages:
    8,740
    Location:
    Avalon Beach NSW
    Hey Paul, good news on the easy fix ! Cheers, Mark
     

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