Clutch math

I've been looking and found nothing I trust. 
 

My question is two parts. 
1- how far does a pressure plate or clutch fork need to move?

2- for a mechanical clutch, is there a general rule for how much leverage you need?

im trying to figure out how long to make levee arms and linkages for the challenge Funderbird. Thanks!

https://americanpowertrain.com/pedal-pusher-how-to-measure-and-adjust-your-clutch-pedal-ratio/

Do a search on clutch linkage design and clutch linkage math.  A lot of stuff comes up.

In reply to jharry3 :

Trouble is, I'm not converting to a hydraulic setup, I'm putting a fully mechanical setup in a car that was automatic. I could just do trial and error fitting I suppose. Easy enough to make everything adjustable. 

barefootskater said:

In reply to jharry3 :

Trouble is, I'm not converting to a hydraulic setup, I'm putting a fully mechanical setup in a car that was automatic. I could just do trial and error fitting I suppose. Easy enough to make everything adjustable. 

Ok.  Being I am an engineer I would approach it this way:

1)  Pick out a pressure plate and get the manufacturer data for the spring rate of the plate. 

2) find out the gap required for the clutch to dis-engage - also from manufacturer.

3) At this point you have to back up through lever arm lengths to calculate mechanical advantage needed to get the pedal force down to where you can manage it and get the dis-engagement gap  you need from the pedal travel available.

4)    Its all Archimedes lever arm stuff.  Statics for us engineering types.  Summing moments about pivot points.    

The early Mustangs I had long ago had completely mechanical systems. The pedal pushed a rod attached to a lever on a shaft.  Another lever had a push rod attached which pressed against the actual lever that held the throwout bearing around the transmission shaft.  So 4 levers through a clutch pedal that moved at least 8 to 10 inches was enough to move the throw out bearing lever arm about an inch and resulted in maybe a 1/8" gap on each side of the clutch disk between the flywheel and pressure plate.  This gap can be measured with a feeler gauge after installation by the way.    You need to work all these dimensions out on paper for sketches and the lever arm math . Its trial and error because  you need to balance clutch travel with how much pressure you want to live with for shifting.    If  you need ideas you could take a look at old cars and trucks with manual transmissions.  They all had mechanical linkage similar to what I describe for the 65 mustang.

  Personally I think the hydraulic system would be way more simple since  you are only sizing a master and slave cylinder and the hydraulic line transmits the force at whatever routing is convenient.

Ths Zoom clutch I had on the 65 Mustang  took about 80 lbs of foot pressure to operate.  Since that was 40 years ago I don't think I could operated that clutch any more.

Short story:

Audi S4 (B5 platform so 2000-ish) required 0.085" or about 2.1mm pressure plate fork displacement, to go from fully clamped to 0.025" clearance between clutch disc and pressure plate. Ignore reading on depth mic, I took the pic before zeroing.

so that's how much throw out bearing travel my setup requires. From there I'd need clutch fork lever ratio to know how much slave piston travel that is, then I'd need to know slave bore to calculate fluid displacement, then I'd need to know master bore to calculate master piston travel. Then I could measure total clutch pedal swing to calculate available pedal ratio .

basically i followed what jharry3 said, except i didn't measure force. because berkeley it, i'm quadzilla.

edit:  except jharry3 said pounds of foot pressure. which makes my head explode, because pounds are a unit of force, not pressure.  and foot is a unit of length as well as the thing we push pedals with.

6:1 hydraulic to 8:1 mechanical for pedal ratio, from something I read years ago. 

Y'all are awesome. Looks like I have some measuring to do. I made sure to leave plenty of room for adjustment and leverage. 
 

hopefully I can get half decent measurements without pulling this trans again. That'd be great. 

From my 60 El Camino:

pedal pivot to center of pedal pad 12.5"

pedal pivot to clutch rod 3.5"

center to center z bar (clutch pedal side) 3.5"

center to center z bar (transmission side) 2.5"

has a stock clutch fork probably pretty much the same as the van one you have. It's running a diaphragm style Centerforce clutch - pedal effort is pretty light for an older car but not compared to newer cars. Pedal travel is about 7". Clutch fork travel at the linkage end is generally 1-2"

Racingsnake said:

From my 60 El Camino:

pedal pivot to center of pedal pad 12.5"

pedal pivot to clutch rod 3.5"

center to center z bar (clutch pedal side) 3.5"

center to center z bar (transmission side) 2.5"

has a stock clutch fork probably pretty much the same as the van one you have. It's running a diaphragm style Centerforce clutch - pedal effort is pretty light for an older car but not compared to newer cars. Pedal travel is about 7". Clutch fork travel at the linkage end is generally 1-2"

Dude! You rock!

I just pulled all that linkage stuff out of my ‘69 Cougar to change to  hydraulic system.  I can take pics and dimension them prior to posting them.  I need to pull the pedal box to swap to bearings so I’ll give you those dims as well.