Clutch Master cylinder size

Brian · 10-12-06, 06:57 AM

Looking for the correct master cylinder size to use on my GTD clutch ....I have an R-21 from Mach I, the Tilton Racing clutch and clutch cover, Frank Catt designed throwout bearing,Tilton 6.2:1 pedal set up and the stock(that I know of) slave cylinder. I anticipate using 1/4" to plumb the line.

Many Thanks in advance
Brian

Ian Anderson · 10-12-06, 09:11 AM

Brian
I used the 0.75 inch master on mine and I get the 3/4 inch slave movement on full pedal depression.

But I have tilton pedals at about 5:1 ratio. It all depends on how much liquid you move on the pedal stroke.

Also I found the 0.75 inch master was the biggest one with the holes vertical for mounting to the pedal box - perhaps others are available but I could not find any!

If it does not work I believe others have sleeved down the Renault Slave and this works too.

I used 3/16 brake line and although had thought there may be a problem moving the volume of fluid through the lines have not yet had a problem

Cheers
Ian

Brian · 01-19-07, 06:37 AM

Thanks Ian, the cylinders I am using are available from 5/8" through 1 1/8" in 1/16" increments. I may go larger than your 3/4" to decrease the amount of pedal throw required as I have a higher ratio pedal. But knowing I need 3/4" slave movement puts me on the right track, I just need to do a little math now.

cheers

Brian

Frank Catt · 01-19-07, 06:48 AM

Brian, if you are useing the stock Renault (30) slave cylinder, then you will use either a 7/8 or 15/16 Tilton Master cylinder. If you find this combination gives too heavy pedal pressure for road work, then sleeve down the slave to 3/4 inch bore and use a 13/16 or 7/8 master cylinder, Frank

Dave Bilyk · 01-19-07, 07:54 AM

mmmm, I dont have any comments to help Brian, but interested in the comments so far. I am intending to check my slave cylinder size because, although I have a 5/8" master, my clutch pedal pressure is so heavy that I must make a change. I have no idea what clutch is actually in there, but I was told that it had been changed for something stronger after the original expired. I will check the slave size and travel this weekend.

Brian · 01-19-07, 12:11 PM

Thanks for getting me on target Frank, as always you are a font of knowledge with these things!

Brian

Ian Anderson · 01-19-07, 12:20 PM

Dave

I must be lucky

0.75 Master and Renault Slave and a clutch softer than the Punto!
But perhaps the pressure plate is not really beefy - but it will spin the tyres so must be gripping fairly well!

Ian

Dave Bilyk · 01-19-07, 03:19 PM

As usual I don't have a memory, both master and slave appear to be 1", so I guess that I would need to reduce master to 7/8".
I'm not in the habit of riding the clutch while stationary, but at the moment, I can only hold it for a couple of seconds before my leg muscles start to give way.

Bill Musarra · 03-19-07, 07:40 AM

I am reviving this thread for educational reasons. I would like a primer on slave cylinders/master cylinders/pedal ratios.
If I were using a 7/8" master with 5:1 pedals(Tilton floor mount), would I want a 7/8" slave? I am using the Kennedy setup for a 930. If I wanted to make the pedal softer would I go to a larger master? I guess I need a primer
in ratio and proportion and hydraulic function? A good explanation would help a few of us out.
The next question would revolve around the slave cylinders. Which slaves will work best for our setups? How would I go about figuring this one out? My assumption would be to fined one on ebay that would mount in the right direction on the transaxel. Then I would have to figure out which one of the 20 or so that fit that criteria that would work for my aplication. Making brackets is no problem. Just don't want to buy 3 or 4 slaves to get the right one. Is push better than pull?
Thanks in advance.

Bill

Lynn · 03-19-07, 09:10 AM

Hydraulic Multiplication:

The ratio of the piston sizes (in²) Slave:Master is what determines the mechanical advantage (softness of pedal) in the system. So that if you have a ½" master and a 1" slave, 10lbs of force on the master piston will produce 40lbs of force in the slave. (It is a ratio of the squares of the radii: sr²/mr² = .5²/.25² = 4)

Volume (in²*in) of fluid moved will determine the throw and is the inverse of the above ratio. So in the scenario above, 2" of piston travel in the master will produce .5" of travel in the slave.

Start at the clutch (how far must the throw out bearing move to disengage the clutch) and work backwards. With the 930, you'll also have the ratio of the throw out mechanism arms to work with. (Technically, they come into play in a G50 also, but it is a fixed ratio in this case and can't be manipulated easily.)