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Thread: Brake pipes

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    Brake pipes

    I'm trying to fit a replacement master cylinder and servo from a mk 3 Mondeo to a split brake system ( front / rear ) and seem to remember something about where the pipe to the front discs should be fitted into the master cylinder. Both outlets are the same size. Currently there is a small diameter master cylinder fitted and the pedal travel is long and almost touching the floorboard so hopefully the larger diameter Mondeo unit should hopefully do the trick. Any ideas please. ThanksP1070351.JPGP1070350.JPGP1070349.JPG
    Last edited by stevesteve; 20-03-2019 at 17:45.

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    Off the Xmas card list kapri's Avatar
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    Cylinder bore is the starting point and then add in pedal ratio . First though need to know what brakes used all round , bore, drum disc to work out fluid consumption and then how to get require line pressure.


    Heres a little something I wrote 20 odd years back

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    UK Hot Rods: News, tech, chat, email group for hot rods, street rods and kustoms
    Last edited by kapri; 20-03-2019 at 17:49.

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    What's that cylinder in the front of the first picture do ? It looks like you'll never bleed it ??

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    I'll need to take it all apart to measure things and get definite figures. My thinking on this is a larger M/C would push a greater amount of fluid into the system for the same of pedal movement ,also the applied force would be the same (my right foot ) the larger M/C would result in increased pressure in the system also.?

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    Quote Originally Posted by kapri View Post
    What's that cylinder in the front of the first picture do ? It looks like you'll never bleed it ??
    That's the replacement waiting to be fitted and I agree with those outlet pipes.

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    Quote Originally Posted by stevesteve View Post
    I'll need to take it all apart to measure things and get definite figures. My thinking on this is a larger M/C would push a greater amount of fluid into the system for the same of pedal movement ,also the applied force would be the same (my right foot ) the larger M/C would result in increased pressure in the system also.?
    Nope, it's actually contrary to how you'd think ! LOL Bigger m/c equals LOWER pressure , that's where you have to generate additional pressure by either pedal ratio or servo. The articles explain it all .

    A description of parts used will do for now .

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    Quote Originally Posted by stevesteve View Post
    I'll need to take it all apart to measure things and get definite figures. My thinking on this is a larger M/C would push a greater amount of fluid into the system for the same of pedal movement ,also the applied force would be the same (my right foot ) the larger M/C would result in increased pressure in the system also.?
    As Kev alludes to. Pressure = Force divided by area (P=f/A). If you make the area smaller (with a smaller cylinder) then for the same force at the pedal the pressure rises. It is an inverse relationship.

    Basically for the same applied force:
    If you double the area of the cylinder, you halve the pressure.
    If you halve the area you double the pressure.

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    Yes , correct. Now ive sat and thought through it , it makes sense.
    So today I replaced the M/C and servo with a unit that increases the piston area from 3.142 to 4.5 cm2 Assuming the applied force is the same ( say 70 Newtons ) the pressure has been reduced from 22.2Ncm2 to 15.5 Ncm2 however I can increase the pressure with my right foot further to compensate for the loss easily. The fluid pushed into the system has increased from 15.7cc to 22.6cc and reduced pedal movement to minimal , rock solid, but only when the hoses are clamped off either with engine running or not. If I unclamp the front hoses individually the pedal movement increases accordingly ,not good.
    The original front brakes have been replaced with a kit from Speedway with 11 inch discs and callipers from a 1976 Impala with as far as possible to tell 55mm diameter pistons X2 . What is difficult to understand is with the front hoses unclamped there is considerable pedal movement until the servo is exhausted ( engine switched off ) then the pedal becomes solid.?? none of this has been on the road yet so things may need bedding in??

    Pedal ratio is 5.5:1

    Rear cylinders sizes are 2 pistons at 35mm diameter and two pistons at 25mm diameter . Master cylinder diameter now 24mm was 19 originally 25mm (factory)
    Last edited by stevesteve; 21-03-2019 at 15:28.

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    Off the Xmas card list kapri's Avatar
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    Regretably ther is alimit to how much force can be applied via the pedal . It is usually taken as a 75 pound or 100 if out of your seat.

    What you are observing is all correct.

    Servo allows more 'push' until exhausted and then you are back to maximum manual pedal input.

    Releasing locked off brakes WILL increase travel as they are now moving and consuming fluid

    Correctly sized master will normally give around 10-12mm at M/C so 5.5 times that at the pedal pad itself ie aropund 55mm travel until locked out.

    You really won't get a Yank system to work using Brit componets as out m/c range volume is much less tahn theirs .

    You need to be looking at 1" to 1 1/8" Yank master ( and servo) to supply everything required. I'd advise 1 1/8" as that's their usual sizing for disc drum set up.
    Last edited by kapri; 21-03-2019 at 18:34.

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    Thanks Kapri, looks as though I need to re think what I'm up to.

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