speedyxjs
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| posted on 17/6/08 at 12:00 PM |
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Master cylinder too big?
After my decision not to use my donors pedal box and suggestions to make my own, i have decided to meet halfway and make my own usng parts of the
donors.
The only thing that concerns me is that the master cylinder is quite big, bigger than the ones i have seen people using on here.
Is the one i have likely to be too big?
Im asuming if it were too big i would just keep locking up at every touch of the pedal? 
How long can i resist the temptation to drop a V8 in?
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Mr Whippy
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| posted on 17/6/08 at 12:04 PM |
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even with that ships engine?
I thought you'd need drag parachutes too
Seriously though you should be using a cylinder rated for the brake callipers, so if you’re using the jag stuff you'll need the cylinder for
them. If you’re using ford stuff use the ford one...
[Edited on 17/6/08 by Mr Whippy]
Fame is when your old car is plastered all over the internet
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MikeCapon
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| posted on 17/6/08 at 12:08 PM |
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Perhaps you need one of these
[img][/img]
www.shock-factory.co.uk
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speedyxjs
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| posted on 17/6/08 at 12:09 PM |
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Oh right
Cheers Whippy 
How long can i resist the temptation to drop a V8 in?
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speedyxjs
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| posted on 17/6/08 at 12:09 PM |
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quote:
Originally posted by MikeCapon
Perhaps you need one of these
Image deleted by owner
Thats a funny looking handbrake
How long can i resist the temptation to drop a V8 in?
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Guinness
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| posted on 17/6/08 at 12:22 PM |
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Ideally you want to use a set of braking components that work together to produce the maximum braking effect, yet retain a level of control.
I guess a Jag m/c is going to be quite large because it feeds a set of big brakes? If you use a small m/c with the original Jag brakes you are going
to be in trouble with a very long pedal travel. Similarly, if you use the Jag m/c with some tiny Sierra brakes it just isn't going to be
controllable.
Also think about the pedal effort. I bet the Jag had servo assistance!
Time to sit down, do some measuring / reading up on brakes I think. You need to find out the m/c diameter and stroke, the calipers piston dia /
number etc, whether you are using drum brakes or disc on the back etc etc.
Brakes are no area to mess around with!
Mike
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PAUL FISHER
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| posted on 17/6/08 at 01:31 PM |
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The smaller the master cylinder the greater the hydraulic advantage, giving greater pedal movement and less foot effort for the same braking force. So
with a big Jag master cylinder you would be less likely to lock the brakes without the servo fitted.
Ideally you want a master cylinder around 0.75" bore
[Edited on 19/05/04 by PAUL FISHER]
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britishtrident
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| posted on 17/6/08 at 01:45 PM |
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Most Jags use a 0.9" dia mastercylinder (a shade under 23mm.
Working on the asumption you are using donor brakes and he servo provides 50% of the pedal effort .
Also assuming your completed car will weigh 50% of the original
If you keep the same pedal leverage the brake pedal force will be about the same.
BUT The leverage of the original pedal could be as high as 9 to 1 and even with a 442 chassis getting a 5.5 to 1 leverage is good going.
Assuming you can get a 5.5:1 leverage a 0.75" dia mastercylinder would give about a 20% increase in pedal effort over the original Jag which
is probably acceptable if you consider the donor would be regarded as over servoed by most sporting drivers.
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speedyxjs
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| posted on 17/6/08 at 02:02 PM |
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quote:
Originally posted by britishtrident
Most Jags use a 0.9" dia mastercylinder (a shade under 23mm.
Working on the asumption you are using donor brakes and he servo provides 50% of the pedal effort .
Also assuming your completed car will weigh 50% of the original
If you keep the same pedal leverage the brake pedal force will be about the same.
BUT The leverage of the original pedal could be as high as 9 to 1 and even with a 442 chassis getting a 5.5 to 1 leverage is good going.
Assuming you can get a 5.5:1 leverage a 0.75" dia mastercylinder would give about a 20% increase in pedal effort over the original Jag which
is probably acceptable if you consider the donor would be regarded as over servoed by most sporting drivers.
I am using the donor brakes and i have kept the servo but wasnt sure whether i needed to use it.
I am working on the car being half the weight of the donor.
I was going to cut the pedals down to about half the original size.
How long can i resist the temptation to drop a V8 in?
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britishtrident
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| posted on 18/6/08 at 11:09 AM |
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You really need to measure what the leverage ratio is on the donor and what it will be after you cut the pedal down --- measure to the centre of the
pedal pad.
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speedyxjs
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| posted on 18/6/08 at 11:12 AM |
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quote:
Originally posted by britishtrident
You really need to measure what the leverage ratio is on the donor and what it will be after you cut the pedal down --- measure to the centre of the
pedal pad.
How do i work it out?
How long can i resist the temptation to drop a V8 in?
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britishtrident
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| posted on 19/6/08 at 07:02 AM |
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Pedal Leverage ratio = L1/l2
Where L1 = Distance from pivot centre to centre of pedal pad.
L2 = Distance from pivot centre to centre of hole for master cylinder push rod clevis pin.
On a Locost style chassis getting a leverage rationof over 5:1 is pretty difficult.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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