flak monkey
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| posted on 31/8/09 at 10:11 AM |
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Hydraulic clutch pedal ratios
Before I drill a whacking great hole in my bulkhead...
What sort of pedal ratio should I be looking at for my hydraulic clutch?
I have a 0.75" master cylinder. I have no idea what the bore of the slave cylinder is (is a mondeo one if anyone knows?).
I can either get full stroke on the master cylinder (then fit a pedal stop as required) and have about a 2:1 pedal ratio. Or go for less stroke and
have a higher pedal ratio, but be unsure of if I will have enough travel to disengage the clutch.....
Anyone offer any advice?
David
Sera
http://www.motosera.com
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tomgregory2000
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| posted on 31/8/09 at 10:28 AM |
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2:1 ratio that doesnt sound enough
i think mine is about 5:1 or 4:1
edit:- mine is a .725 and i have spaced the mc out so it is further in the engine bay compared to the brake mc as if i didnt it would put the clutch
pedal at a funny angle, i am using a saab slave cylinder and buy no means do i need the full stroke of the cylinder
edit agen:- dont forget the higher the pedal ratio the smoother the clutch engagement and easy on your leg
[Edited on 31/8/09 by tomgregory2000]
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Volvorsport
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| posted on 31/8/09 at 10:50 AM |
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most clutch and brake master cylinders will be about 3/4 , so youre about right there . they also work on about the same pedal ratios as brake pedals
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the hole in your bulkhead will be the same regardless of what size master cylinder you put in there !!
www.dbsmotorsport.co.uk
getting dirty under a bus
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flak monkey
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| posted on 31/8/09 at 11:04 AM |
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quote:
Originally posted by Volvorsport
most clutch and brake master cylinders will be about 3/4 , so youre about right there . they also work on about the same pedal ratios as brake pedals
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the hole in your bulkhead will be the same regardless of what size master cylinder you put in there !!
Yeah, the main thing is getting that hole in the right place to give enough stroke on the master cylinder to ensure the clutch disengages properly.
How much stroke have other people got on their master cylinder?
The main issue is not being able to find out what the bore size of the slave cylinder is. If I had that info, it would be easy...
Its a slave cylinder from a mondeo CSC002 if anyone has access to the required info?
David
Sera
http://www.motosera.com
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rusty nuts
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| posted on 31/8/09 at 11:42 AM |
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What's pedal ratio on the Mondeo?
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speedyxjs
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| posted on 31/8/09 at 12:16 PM |
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I set mine at 5:1 on my jag one and have about 1/2 inch travel before biting point
How long can i resist the temptation to drop a V8 in?
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britishtrident
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| posted on 31/8/09 at 01:10 PM |
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As Volvosport said hydraulic clutch and brake pedal ratios on tintops tend to be the same ( about 8.5 to 9.5:1)
On british cars the standard bore was 0.75" or sometimes 0.7" or 0.625"
[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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flak monkey
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| posted on 31/8/09 at 02:03 PM |
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OK, so I have done some messing about in the garage.
The total volume displaced by the clutch slave cylinder from retracted to extended is 13cc over a total stroke of 20mm.
My 0.75" master cylinder has a total stroke of 40mm which will displace 11.34cc
It seems to be common that you need to depress the clutch fingers by about 6mm to disengage the clutch. So I would need to have a stroke on the
mastercylinder of approx 13mm to acheive this.
So playing it safe, say I need 12mm of slave cylinder movement, I then need 25mm stroke on the master cylinder to get this.
This will give me about a 4:1 pedal ratio.
I dont stand a hope of getting 8:1 and still getting enough master cylinder stroke to disengage the clutch. Plus I reckon there will be no feel at
that sort of ratio 
For comparison, my brake pedal is only 4:1 or there abouts, without a servo and with a 22mm m/c. Still locks the brakes easy enough
Sera
http://www.motosera.com
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britishtrident
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| posted on 31/8/09 at 03:05 PM |
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Most important not to have too much movement at the slave cylinder end or you will damage the pressure plate or fork, Most of the available movement
in the slave cylinder is to allow for hydrostatic adjustment for clutch wear.
When the pedal is pressed you only need enough actual working stroke at the slave cylinder end for the pressure plate to lift just enough to clear
the driven plate.
[Edited on 31/8/09 by britishtrident]
[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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