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Thread: Heavy Clutch

  1. #1
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    Heavy Clutch

    Hi ,

    I need to lighten my clutch pedal as it is very heavy, present girling 625 bore with T5 box with thrust bearing dax pedal . I am looking at options . Pedal travel is very small at present to shift .

    1. Replace master cylinder 0.5 bore . Ford do a girling rally version. https://www.carbuildersolutions.com/...hout-reservoir

    2. Try and change the ratio pivot point . The master cylinder pedal . Does not look to be much room .

    3. Fit servo but the feel and loss of control is my worry

    I did notice that the angle of the piston at starting point is not straight but straightens as the pedal is depressed.

  2. #2
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    Going smaller will make it heavier, try going larger on the master size, 0.7 or even 0.75"

  3. #3
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    http://www.cobraclub.com/forum/showthread.php?t=55406

    The above link may help?? Thanks Lee
    .............never drive faster than your guardian angel.

    cobraclub.com/gallery/showgallery.php/cat/633 - this is the link to my build photo's you have to put w w w . h t t p : / / in front of it!!

  4. #4
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    Quote Originally Posted by tonym View Post
    Going smaller will make it heavier, try going larger on the master size, 0.7 or even 0.75"
    Are you sure? Smaller bore will shift less fluid for the same pedal travel and the clutch will move correspondingly less.
    Cheers

    Myles D-W

  5. #5
    Join Date
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    I agree with Myles, a smaller master cylinder bore will have less resistance but give longer pedal travel.
    I usually use a pair of 7/8" cylinders (0.875").
    Kev Davies
    South Wales Area Rep. UKCC Membership Secretary
    DAX Mk4, 383 Chevy Stroker, Tremec. SOLD
    Contemporary CCX 3-4028, 445ci Big Block FORD FE,TKO 600, Old School IVA'd and SOLD
    Dax De Dion LS2 and T56 IVA'd June '17 SOLD
    1965 Ford Mustang 289 Convertible FOR SALE
    In build- Hawk 289 Sebring

  6. #6
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    Tony is right, even if you go smaller bore on the pipe diameter, it's gets stiffer, you are trying to push the required volume to activate the clutch through a smaller orifice.

    There is a proven balance of master cylinder, pipe diameter and slave cylinder that works well, I know the master cylinder used is usually 3/4" or 0.75", tube bore if I remember and someone can correct me if I'm wrong is 3/8 the slave I can't remember! Maybe 7/8ths

    I still had a heavy clutch due to having a heavy duty pressure plate BUT the pedal ratio in the AK was nowhere near the 6:1 ideal pedal ratio.hence why I fitted a clutch servo and moved the pivot point.

    Lee
    .............never drive faster than your guardian angel.

    cobraclub.com/gallery/showgallery.php/cat/633 - this is the link to my build photo's you have to put w w w . h t t p : / / in front of it!!

  7. #7
    Join Date
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    Agreed a smaller bore hose / pipe will give you higher resistance I always use -4 hoses. Some use smaller -3 brake pipe and get away with it.
    But I stand by a smaller master cylinder is going to give a lighter pedal than a larger one. (with the trade off of a longer pedal).
    It's simple physics about surface area and all that.
    Kev Davies
    South Wales Area Rep. UKCC Membership Secretary
    DAX Mk4, 383 Chevy Stroker, Tremec. SOLD
    Contemporary CCX 3-4028, 445ci Big Block FORD FE,TKO 600, Old School IVA'd and SOLD
    Dax De Dion LS2 and T56 IVA'd June '17 SOLD
    1965 Ford Mustang 289 Convertible FOR SALE
    In build- Hawk 289 Sebring

  8. #8
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    I used -3 at 1st but it was no good, it's achieving the best balance there is a lot of threads on here to search through. Some of it is trial and error but this method is costly.......like everything else with cobra' s!
    If you still need more help give us a ring thanks Lee
    .............never drive faster than your guardian angel.

    cobraclub.com/gallery/showgallery.php/cat/633 - this is the link to my build photo's you have to put w w w . h t t p : / / in front of it!!

  9. #9
    Join Date
    Feb 2011
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    281
    Cobra 289 (Carlos) has a website with a spreadsheet - clutch calculations, which is very useful in working out how to get the pedal pressure you want.

    http://www.donostia.demon.nl/

  10. #10
    Join Date
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    I agree that a smaller bore master cylinder will move less fluid and lighten the pedal but you also say that there is very little pedal travel so a combination of a smaller bore master but an increase in the pedal travel sounds like a good direction to try.

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