Changing the slave for more pedal throw

[EZ-E]

I have been reading through searches and I don't want to sound stupid and I also don't want to make a mistake as well.

From what I have read and gathered from my search and reading is that, if you would want more pedal throw or adjustment, with the stock bore clutch master cylinder, you would have to go with a smaller slave cylinder, like that of the 240SX.

Same situation in reverse as if you went with at larger then 5/8 bore clutch master cylinder, and the stock slave, you would get more pedal throw.

Reason is that I am asking is I would like a bit stiffer pedal, and a bit more throw and adjustability.

So with having the stock bore master cylinder, going to a 240SX slave would give me this correct?

Thanks,

[blueovalz]

EDIT: Pedal movement and pedal pressure do not move together (both do not increase together, nor decrease together). It's like using a cheater pipe. You may be making the pushing force (or pressure on the pipe) smaller with a longer pipe, but the throw will increase (get bigger).

 

Going to a smaller (bore size) slave cylinder will make the pedal stiffer, but much more sensitive as well (less modulation) because the piston in the slave cylinder has more travel than one of larger bore (provided the master cylinder has not changed)

 

Reason is that I am asking is I would like a bit stiffer pedal, and a bit more throw and adjustability.

The pedal will be stiffer, but the throw will be shortened as well.

 

To get both, you need a stiffer (higher pressure) pressure plate, and then go to a larger slave cylinder, but you'd need to know a lot of other information about specific bores sizes and pressue plate info for this to end up just as you wish.

[bjhines]

Ummm... blue... that first part is hard to follow....

 

I think EZ-E has done his research.... It sounds like he has the right idea....

But the addition of a stiffer pressure plate is the only way to get increased throw AND a stiffer pedal.

[JMortensen]

Here's a different analogy which helps me out that a friend shared with me. Think of master/slave hydraulics like bicycle gearing.

 

If you go with the small sprocket on the front, that makes it easier to pedal, but you don't go as far. Small master = less pedal pressure required and less throw. Large front sprocket is like a larger master = more pedal pressure required more throw. At the slave end the analogy continues: large slave = easier pedal pressure and less throw, small slave = more pedal pressure and more throw.

 

The funky part is when you're talking about brakes, because when you talk brakes you might want to think that more throw = more braking, but that is NOT the case. Once the pistons push the pads onto the rotors or the shoes into the drum the throw part of the deal is over, now its the torque multiplication that matters, and we all know that you get more torque multiplication with the big sprocket on the back of the bike than the small one. So a bigger caliper piston despite having less throw will transfer more torque to the brake pads or shoes.

 

In this clutch situation though what you need is enough throw to completely disengage the clutch, but not too much where you overextend the pressure plate springs.

[blueovalz]

Small master = less pedal pressure required and less throw

 

Rarely is Jon confused, but I'm going to accuse him of such anyway :wink: NOD. With the bicycle analogy (which is a very good one), a smaller front sprocket would indeed result in less pedal pressure, but would also require MORE throw (yes, less distance traveled, but the crank throw is increased). The cyclist would be pedaling more revolutions at the crank to go the same distance than if he used a larger front sprocket.

 

Large stroke X small pressure = small stroke X large pressure.

 

In hydraulic systems between two pistons connected through a single line (just as a brake or clutch system is), the MC/SC bore size ratio (Master Cylinder to Slave Cylinder bore ratio) is what determines stroke and pressure between the two end pistons. The SC piston stroke is directly proportional to this ratio, and the SC piston pressure inversely proportional to this ratio.

 

Thus you cannot get more stroke (more modulation) and more pressure at the same time by solely changine bore sizes. Changing the pedal geometry could have the same effect. Increasing the stroke by changing the pedal's folcum point would provide more or less pressure, but less or more stroke.

[JMortensen]

Rarely is Jon confused, but I'm going to accuse him of such anyway :wink: NOD. With the bicycle analogy (which is a very good one), a smaller front sprocket would indeed result in less pedal pressure, but would also require MORE throw (yes, less distance traveled, but the crank throw is increased). The cyclist would be pedaling more revolutions at the crank to go the same distance than if he used a larger front sprocket.

You caught me Terry! I was thinking throw AT THE OTHER END vs the larger master. You are entirely correct that the smaller master requires more throw at the pedal to do the same job as a larger master. Gotta watch me. I make careless errors like that sometimes. Never trust my math either...

 

Sorry for the confusion.

[2126]

Hey guys, sounds to me like its time for a refesher course or review of Pascal's Law and Bernoulli's Principle! Not that I think you guys don't know what you're talking about but, sometimes a little refresher on these laws and principles do help to explain them to someone unfamiliar with hydraulics!

[blueovalz]

Pascal, yes, Bernoulli...hmm, I'm not sure how I could use that in my explanation (but my formal education could be refreshed). Anyway, I wanted kill the fly with a fly-swatter instead of a cannon.

[bjhines]

LOL..... What flyswatter..... Isn't putting a V8 in a Zcar leaning a little more towards the cannon...

[blueovalz]

Well, it's a small cannon though

[fastzcars]

That's a good one Terry:biggrin:

[240hoke]

Something that might be very helpful to you is to make a quick spreadsheet in excel. using pascal's law and some basic algebra you can see what the change in Master cylinder or slave cylinder will have regarding the force required to engage the clutch and the maximum possible throw of the slave.

 

I just did this when swapping clutchs, I am in the process of changing out both the slave and the master to get the correct throw I wanted.

 

A pathfinder slave (11/16") will provide you with a little more throw then the stock setup. It helped my issue but wasnt enough. I have a 3/4" master cylinder on the way. this will make the pedal stiffer but get my engagement at the top of the pedal stroke.

 

Hope this helps

[blueovalz]

Make sure we are all speaking with the same definition of "throw". The original question referenced "throw" to pedal travel (unless I misunderstood), but most folks reference "throw" to the end result at the slave cylinder piston travel.

[240hoke]

Well the throw of the slave is going to be directly related to the throw of the pedal. I was talking about the throw of the slave.

 

What I was also trying to say is that the only readily availible option for a smaller slave is the pathfinder slave (for a l motor, i did look that hard either) which is 11/16". There is a MUCH broader range of sizes availible when looking for masters. Jeg's and summit carry 3/4, 13/16,7/8,15/16. A slave will be alot cheaper ($16) but its not going to give you the same ajustability as the master since you can go to a larger size, however the master's require more modification and will run ~$70.

[duragg]

I currently love this thread as I want a little more slave throw.

I bought an 11/16 with the adjustable rod, but have the stock fork without the hole.

Tempted to drill and slot the hole and put a spring so it all act correctly.

 

Or just see is a 5/8 slave might be available.

[duragg]

I currently love this thread as I want a little more slave throw.

I bought an 11/16 with the adjustable rod, but have the stock fork without the hole.

Tempted to drill and slot the hole and put a spring so it all act correctly.

 

Or just see is a 5/8 slave might be available.

Measured my clutch slave throw at about 17mm. It is stamped "AS 05" and has 3/4 bore.

Bought an adjustable early 1970-1972 type with 11/16 bore.

I used the non-adjustable pushrod which fit nicely, bleed and measured a bit over 19mm throw.

 

This now allows me to adjust things so my clutch doesn't begin to engage a 1/2 " off the floor.

Pedal is stiffer (more manly).

[daddydonuts]

What causes the slave to come all the way out of the bore when I push in my clutch pedal? System is bled, pedal is adjusted within tolerance according to the FSM. I bought a NAPA brand slave and have maybe 20 miles on it.

Edited January 27, 2014 by daddydonuts

[duragg]

The later style has a spring inside which acts to compensate for wear. Did you open bleeder and push piston to bottom of bore? And does that result in too much clearance between salve piston and fork? On mine they are just touching, i can just slightly turn the rod as it rests lightly on the fork.

 

Thinking.. If your rod is too far from fork with piston at bottom, the piston spring will compensate for this and your starting place would be too far out and thusly your extended is outside the bore? Does the o-ring protrude?

 

Make the rod longer?

[daddydonuts]

The later style has a spring inside which acts to compensate for wear. Did you open bleeder and push piston to bottom of bore? And does that result in too much clearance between salve piston and fork? On mine they are just touching, i can just slightly turn the rod as it rests lightly on the fork.

 

Thinking.. If your rod is too far from fork with piston at bottom, the piston spring will compensate for this and your starting place would be too far out and thusly your extended is outside the bore? Does the o-ring protrude?

 

Make the rod longer?

I pushed the piston all the way in and it does not even come close to the clutch fork, and when I bleed it, the piston comes all the way out...makes me think my clutch fork is bent or I have the wrong type of slave. 73 240Z 4 speed Edited January 27, 2014 by daddydonuts

[NewZed]

Hope it's not the case, but it could also be the wrong, short, throwout collar.  You can get an idea by looking at where the fork sits in its hole, and its angle, when it's pressed against the collar.  If it's angled back and sitting at the back of the hole, that's a problem.  Could also be an issue with the fork pivot pin, though that would be uncommon.