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Refitting Master cylinder

Discussion in '308/328' started by maurice70, Jun 18, 2007.

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  1. maurice70

    maurice70 F1 Rookie

    Jan 25, 2004
    4,333
    Sydney
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    maurice T
    #1 maurice70, Jun 18, 2007
    I have recently removed my master cylinder and the brake booster and had the booster overhauled and got a new replacement master cylinder on my 308GT4.Now I have put it all together and I think I might have a slight vacuum leak.I've tested the hose and its ok and the one way valve is new.I can pull a vacuum on the booster using a vac pump but it doesn't seem to hold for more than 20secs under vacuum.The questions that I have is when I removed the original master cylinder it was really tight and it didn't have a gasket and when I refitted the replacement one it was tight but not as tight.I think I might have a leak there.Is there supposed to be a gasket? The other theory is I didn't check the clearance of the brake booster push rod and maybe the booster might be slightly engaging therefore the vacuum is being lost that way.I dont believe that this is the case as I think it would be dragging on the brakes and it rolls ok but hey thats why I am asking.Driving the car the brakes dont feel 100% more like 90% but then again I haven't gone for a good run and haven't had a chance to warm up the brakes either.I have bled the brakes and have flushed out the old fluid.The pedal is hard so I don't believe that there is air in the lines.The other thing it could be is the rebuilders didn't do a good job on the booster.Any takers???
     
  2. dstacy

    dstacy F1 World Champ
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    Jan 23, 2006
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    Dave
    #2 dstacy, Jun 18, 2007
    Looked at 2 different parts books and I don't see a gasket.
     
  3. chrismorse

    chrismorse Formula 3

    Feb 16, 2004
    2,150
    way north california
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    chris morse
    #3 chrismorse, Jun 18, 2007
    I just had some machine work done to mount a wilwood master cylinder to the stock booster.
    There was a gasket about 1/4 inch thick that fit around the tubular section and was compressed into a recess inthe MC unit.
    The photo shows the machining to the wilwood unit, the tube snout and mounting ears that are necessary to make it work.
    I am ignorant of the booster interior, but if vacuum is applied to the chamber that the mc projects into, i don't think that the metal to metal seal of the mc to the booster would likely be airtingt.

    hth,
    chris
     
  4. greg328

    greg328 F1 Rookie

    Nov 17, 2003
    4,209
    Austin, TX USA
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    Greg
    #4 greg328, Jun 18, 2007
    On my 77 GTB, the master cylinder bolted to the booster w/ no gasket. No need for that connection to be airtight/fluid tight--the booster rod simply pushes into the MC to provide pressure on the internal MC, thereby forcing brake fuid out into the system.

    I switched my stock 23mm MC out to t 25mm MC to accomodate my larger brakes.. I know the system well! :)

    Greg
     
  5. maurice70

    maurice70 F1 Rookie

    Jan 25, 2004
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    maurice T
    #5 maurice70, Jun 19, 2007
    Thanks guys.I was expecting Greg or Chris to chime in as my Search option led me to both of your recent posts regarding brakes and boosters.So what do you guys think could be the problem?I dont think its a push rod clearance issue as the brakes would bind when the engine is on.I got the replacement master cylinder from Superformance in the UK.Should I try removing the master cylinder and try fitting a gasket of some sort?
     
  6. maurice70

    maurice70 F1 Rookie

    Jan 25, 2004
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    maurice T
    #6 maurice70, Jun 19, 2007
    Ok guys I found the problem.I decided to back track my steps and see if I could pinpoint the leak.I pressurised the booster and could hear a slight hiss.It was coming from the 90 degree connection that connects the hose to the booster.When I re fitted this there are two copper washers that seal it.I must have dropped the one closest to the booster as it was missing.I replaced the washer and leak tested again under pressure.It held a perfect vacuum.Thanks again for the replies.
    PS:On a side note I'm thinking of getting Porterfield R4s brake pads.What are the pros and cons of these pads?All four brake hoses have been replaced.Thanks
     
  7. kiwiokie

    kiwiokie Formula 3

    Aug 19, 2013
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    John McDermott
    #7 kiwiokie, Jun 14, 2020
    Awakening an old thread. I had both booster and master cylinder rebuilt by White Post and am now assembling. The factory diagram shows a 0.7mm clearance between the booster piston and master cylinder. For those that have done this before did you verify this measurement and if so, how did you go about it?


    Sent from my iPhone using FerrariChat
     
  8. kiwiokie

    kiwiokie Formula 3

    Aug 19, 2013
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    John McDermott
    #8 kiwiokie, Jun 14, 2020
  9. ferrariowner

    ferrariowner Formula 3

    Feb 21, 2014
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    Mansfield, TX
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    Ron
    #9 ferrariowner, Jun 15, 2020
    As I recall the seal is inside the booster. It can be damaged. You should slightly lube it before inserting the MC so it doesn't tear.
     

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