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Master cylinder sizes

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2011/07/12 20:14:04 (permalink)
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Master cylinder sizes

Hi guys

Having problems with the rear brakes locking up first on my mk1. im running volvo calipers up front and r31 calipers on the rear, .7 size master cylinder for the volvo's and .75 for the r31 calipers. Even playing around with the bias adjustment cant stop the rears locking first. checked the front brakes and there working correctly, Just wondering it the .7 is too large, should i be changing it to .625??

thanks Tobie
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    Paul Dunstan
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    RE: Master cylinder sizes 2011/07/12 22:59:01 (permalink)
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    Hi

    What size rotors are you using front and rear?

    If you have the BMW (260mm) front and Audi (245mm) rear the you have a 70/30 front to rear bias - this should be able to be fine tuned to achieve the desired balance!

    Are you sure the Volvo callipers are working 100%? Have you made sure you have "brigded" to all 4 pistons on the Volvo callipers? If not you'll only have half the volume and reduced braking effort on the fronts. If this is the case you'll have a 53/47 split and causing the rears to lock prematurely.

    Swapping to a 0.625 front only you'll have a 74/26 split which may be pushing it a little far forward. Placing a 0.625 front and rear should provide an approximate 66/34 split.
    #2
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    RE: Master cylinder sizes 2011/07/13 19:05:01 (permalink)
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    Thanks for your reply Paul,

    Im running Capri 245mm vented discs up front and Audi 245mm solid rear discs,

    Im running a "T" piece up front for the volvo calipars, ill double check that all four pistons are working.

    thanks
    #3

    Paul Dunstan
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    RE: Master cylinder sizes 2011/07/13 22:51:26 (permalink)
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    OK, although the diff between braking effort of the 245 and 260mm is negligable.
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    RE: Master cylinder sizes 2011/07/14 21:08:26 (permalink)
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    Hi Paul,

    Checked the front calipers and they are working, was unable to turn the disc with a prybar through the wheel studs with the brakes applied.

    I did notice that with the master cyinder pistion rod threads that screw into the balance bar are not even, with the rod being shorter for the rears compared to the front, i suspect is my problem of not being able to adjust the bias correctly, your thoughts??
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    Paul Dunstan
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    RE: Master cylinder sizes 2011/07/14 23:43:25 (permalink)
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    Hi Tobie

    With the brakes applied at full working pressure (decent press) the bias bar must be at 90 degrees to the horizontal plane of the push rods.

    http://www.wilwood.com/TechTip/TechPedalTip.aspx

    With the brakes released the front master cylinder rod should be longer as it should have the most travel to apply the front callipers. That's because the front callipers have a greater volume yet the front master cylinder volume is less than the rear master.
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    RE: Master cylinder sizes 2011/07/20 20:53:41 (permalink)
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    Thanks for that info Paul,

    Ill give adjusting the bias a go this weekend, also the weather in Adelaide this weekend doesnt look to promising for a test drive
    #7
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