308 master brake cylinder, help | FerrariChat

308 master brake cylinder, help

Discussion in '308/328' started by pbat, Jul 10, 2012.

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  1. pbat

    pbat Karting

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    Peter B
    --------------------------------------------------------------------------------

    Hi all, a few weeks ago I fitted a new master brake cylinder on my 308 GTS, and after driving it for ten minutes the brakes started to lock up. I thought it might be something to do with the vacuum to the slave cylinder so I released the vacuum but it wasn’t this, so I bled the lines again, but after driving it for one or two hour it happens again and I have bled the brake for the last time. Does anyone know what could be coursing this?

    Thanks
    peter
     
    pbat, Jul 10, 2012
    #1
  2. don_xvi

    don_xvi F1 Rookie

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    "Lock up" as in the brakes become very sensitive and a light application causes the brakes to lock, or "lock up" as in the brakes apply by themselves? The latter is probably (which I suspect is what you mean) a binding in the linkage. Perhaps you've got a bit of a mismatch on the length of the pushrod with your new MC.
     
    don_xvi, Jul 10, 2012
    #2
  3. 166&456

    166&456 Formula 3

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    Exactly - that must be the problem. If the cylinder is slightly pushed in, the MC starts to work as a diode and expanding fluid from the system cannot flow back to the reservoir. Pressure builds as the brakes get warm, brakes get warmer, pressure builds further, etc.
    A brake booster has a little rounded 'tip' that pushes on the MC piston, under this tip there are generally one or two shims to adjust free play to the MC, you may need to remove some. It can also be you have an incorrect MC.
     
    166&456, Jul 10, 2012
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  4. chrismorse

    chrismorse Formula 3

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    Try adjusting the push rod length. It sounds like the piston is not retracting back far enoughto allow the fluid pressure to escape back into the reservoir
    chris
     
    chrismorse, Jul 10, 2012
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  5. pbat

    pbat Karting

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    Thank you chris, I will try to adjust the push rod tomorrow.
     
    pbat, Jul 10, 2012
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  6. pbat

    pbat Karting

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    Thank you
     
    pbat, Jul 10, 2012
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  7. pbat

    pbat Karting

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    I purchased it from Superformance UK, it looks right. Hope I can adjust this rod. I will try this tomorrow, Thanks again
     
    pbat, Jul 10, 2012
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  8. pbat

    pbat Karting

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    From the advice I have been given for the brakes come on without pressing the pedal. I did removed my new master cylinder again and adjusted the metal shaft from the slave to the master cylinder. I needed to adjust it in 4mm to have it just hitting the cylinder. Today I drove it for an hour and every thing is ok, there is more travel in the pedal now, but what a relief. I am an expert at these brakes now. Thank you all again.
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    Last edited by a moderator: Sep 7, 2017
    pbat, Jul 13, 2012
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