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Brake Failure (Causes?)

  • 17-09-2012 09:32AM
    #1
    studiorat
    Closed Accounts Posts: 6,408 ✭✭✭


    Ok, Bedford CF 250.

    Got into to start it up and run it around the block yesterday. The brakes don't work until the pedal is on the floor. When the engine is off I can build up a certain amount of pressure by pumping the pedal. This pressure is lost as soon as the engine is started again.

    No obvious leaks in the hoses to the drums etc. What gives? Why does the system loose pressure when the engine is running?


Comments

  • #2
    hi5
    Registered Users, Registered Users 2 Posts: 3,107 ✭✭✭hi5


    Maybe the system needs bleeding, when the engine is running the vacuum assisted servo will let you push the pedal all the way down.
    Now might be a good time to change the fluid too.


  • #3
    CJhaughey
    Registered Users, Registered Users 2 Posts: 14,679 ✭✭✭✭CJhaughey


    Its called Diesel creep.


  • #4
    studiorat
    Closed Accounts Posts: 6,408 ✭✭✭studiorat


    In a petrol engine?


  • #5
    CJhaughey
    Registered Users, Registered Users 2 Posts: 14,679 ✭✭✭✭CJhaughey


    Maybe it should be called pedal creep. Its common in diesels but you see it in some petrols as well.
    You haven't pushed the pistons back in the brake calipers for any reason lately?
    This sometimes causes the servo seal to flip and lose pressure like that as well.


  • #6
    studiorat
    Closed Accounts Posts: 6,408 ✭✭✭studiorat


    Haven't touched it. Did about 300 miles in it two weeks ago. Usually give it a spin once a week or so just to keep an eye on it.

    I'm guessing there's a problem with a valve between the engine and master cylinder alright. Just wondering which end of the hose to look at first!!!


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  • #7
    ianobrien
    Registered Users, Registered Users 2 Posts: 2,755 ✭✭✭ianobrien


    I had something similar happen before, but it happened when I was heading down the driveway (it was downhill) to a pair of rather stout gates. I lost practically all brakes and like that the pedal was at the floor, with no obvious leaks.

    It turned out that the seals in the master cylinder tore and I had to get the master cylinder re-built. I also had to change the pants as I had a vision of the car buried in the gates/pillars/wall. Thank God for handbrakes......


  • #8
    selfdiy
    Registered Users, Registered Users 2 Posts: 191 ✭✭selfdiy


    If there are no signs of leak at any of the wheels and you haven't done any work on the brakes recently, i'd bet the master cylinder is leaking possibly to the inside of the servo.


  • #9
    twebb
    Registered Users, Registered Users 2 Posts: 56 ✭✭twebb


    maybe water in brake fluid??? Defo change fluid and see if it sorts it...


  • #10
    beanderb4
    Registered Users, Registered Users 2 Posts: 80 ✭✭beanderb4


    Also loss of pressure could be due to a calliper sticking and keeping a brake on. Heat builds up at the calliper and as a result the fluid heats up too and pressure is lost. Run it for a while and check if the wheel hubs are hot after the run. It's easy to fix a ceased calliper yourself.


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