nick205
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| posted on 29/10/03 at 11:17 AM |
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Master cylinder pushrod
Can anyone who's built/building an Indy recommend how far up the brake pedal from it's pivot point the master cylinder pushrod clevis pin
should be mounted.
Hope that makes sense!
Cheers
Nick
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Simon
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| posted on 29/10/03 at 02:27 PM |
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Nick,
I'm not building an Indy, and I'm guessing you're making your own p/box, but...
I think you are basically trying to work out the ratio between your foot and the master cylinder.
Recommendations seem to vary from about 4:1 (strong legs) to approx 7:1 (not so strong legs)
I'm going to make my own, so following may be of some help.
The pivot can be mounted as close to floor as possible (allowing sufficient material around pivot, so say an inch and a half (allowing
12.5mm/0.5" pivot bar) ie 19mm/0.75" from bottom of bar to bottom of p/box.
Work out where you want the pedal pad (centre) to be - mine 23cm/9"
I therefore have a distance of 20.5cm from centre of pedal pad to centreline of pivot bar.
Ratio wanted is 4.5:1, so 20.5/4.5 = 4.56cm from centre of pivot bar.
That's my maths anyway.
Anyone care to correct - please!
You will also need to take into account the amount of movement this will generate, and therefore the quantity of fluid. You may need larger or smaller
master cylinders.
HTH
ATB
Simon
[Edited on 29/10/03 by Simon]
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CairB
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| posted on 29/10/03 at 03:15 PM |
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Nick,
I put the standard Sierra master cylinder, without servo at 65mm up from the floor. I used a cut down and rounded push rod and clevis from Merlin
mounted at about 45 mm up from the pivot point on the MK supplied pedal. The foot contact point on the pedal is about 190mm which gave a ratio of
about 4.2 /1. This position puts the force inline with the piston to reduce side loading.
Passed SVA OK but I would be tempted to try to get a tad bit more leverage to reduce foot loading, say 5/1 by mounting at 38mm from the pivot.
I think that later Indies have the master cylinder hole already in so this may affect the cylinder height.
Cheers,
Colin
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nick205
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| posted on 29/10/03 at 05:03 PM |
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Thanks for the info Colin!
My Indy chassis does already have the M/C hole cut in, so I've mounted the Sierra M/C accordingly. I'll make some measurements and aim
for a ratio of 5:1 as you suggest.
I'm planning on making an adjustable pushrod, so I can play about with the pedal position a little.
See picture in my archive - ADJUSTABLE PUSHROD
Cheers
Nick
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Mk-Ninja
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| posted on 29/10/03 at 05:13 PM |
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Nick
You say that you didnt use the servo, is this because it wont fit or because it would make the brakes to sensitive.
Gordon
I'm sure I've got one, just don't know where I've put it
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CairB
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| posted on 29/10/03 at 07:08 PM |
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Nick,
The pushrod I got and tweaked from Merlin Motorsports looks just like your drawing.
Gordon.
The thinking goes - the weight of the car is about half the donor, or less in your case. I believe that the servo contributes around 50% at max. So
the loss of vehicle mass compensates for the lack of servo. There is the bonus of more braking feel without the servo. All this is good as it's
a bit tight for space for the servo with floor mounted direct operating pedals on an Indy.
Cheers,
Colin
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nick205
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| posted on 30/10/03 at 10:49 AM |
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Gordon,
No room to fit the standard Sierra servo in the Indy. I have seen remotely mounted servos from AP Racing in the Burton Power catalogue, but
they're not cheap. Also as Colin says the general consesus is that the braking is good enough without a servo.
Colin,
I'm going to have a go at making it and see how it works. It's handy to know that I'm on the right track !!!
Cheers
Nick
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