Do math before doing time

[spd4me]

I though if I increased bore size of clutch master cylinder, it would increase stroke of slave. I installed 1" bore master and clutch became totally inoperable (didn't work). Pushed so hard on pedal it blew out seal on slave. Went to web site www.hotrodheaven.com/tech/brakes and found interesting math. 100 lbs applied to pedal (6:1 ratio which most wilwood pedal are) with 3/4" master will produce 1359 psi. 100 lbs on 1" master will produce 764 psi. So I put back on my old 3/4" bore master and it worked. Average person can push 120 lbs with foot.
bob

[Jim Harding]

I don't know Bob.... I did the exact same thing, and my stroke increased enough to properly disengage the clutch. Have not had any problems with excessive pressure blowing out the slave. Only down side I've noticed is the increased peddle effort to operate the clutch.

[JeepSnake]

Increasing the bore of the master cylinder will increase the linear movement of the slave cylinder because you're moving more fluid volume. The tradeoff is the lower pressure, and thus higher leg effort required.

Bob, it almost sounds like the setup with the 1" master overextended the slave, which then stopped dead (when the clutch fingers hit the pressure plate, or when the piston reached its internal limit), allowing you to build up enough pressure when pushing hard to blow the seal out.

I had a similar situation with the mechanical clutch linkage on a Jeep. When first installed, it was WAY too long. This pushed the fingers of the clutch down into the face of the pressure plate, making it feel like the clutch had not disengaged. So, I kept adjusting the linkage even longer, trying to "get enough movement to make it disengage." Finally, in frustration, I started adjusting the linkage shorter, and got the doggone thing to working!

[spd4me]

Zach- I know it sounds crazy. I could remove slave push rod from fork and it would move 1". Hook back to fork and wouldn't budge. I would adjust all slack out until throw out bearing was against fingers and wouldnt budge. Guess I'll just have to live with grinding into reverse.
bob

[JeepSnake]

Bob,

What slave cylinder are you running, etc.?

It would be nice if the clutch / throwout bearing companies could provide us with specs on how much movement you need in the throwout bearing to disengage their clutch. That would at least give us a starting point for working backwards to figure required slave-cylinder stroke. (Maybe they do, and I've just never seen it???)

I've had good luck with the Wagner/Lockheed type push cylinder (except for my failure to properly inspect and maintain it last year; doh!).

[Naumoff]

Zach- I know it sounds crazy. I could remove slave push rod from fork and it would move 1". Hook back to fork and wouldn't budge. I would adjust all slack out until throw out bearing was against fingers and wouldnt budge. Guess I'll just have to live with grinding into reverse.
bob

What slave are you running?

I would call Willwood and tell them what you have and what amount of movement you need at the slave and see what they recommend.

Has it always grinded when putting it into reverse or has it just started?
Is the clutch wore out?
Have you tried adjusting the clutch pedal out to increase stroke of the master ?

Here is why it is easier to push the pedal with a smaller bore master. Longer stroke w/ less effort but you lose movement on the slave.
Increase size of master and you have to increase your effort but gain movement in the slave.

[Tony Radford]

Having invested a few million hours on this topic myself, I learned that the greater the clamping pressure of the clutch, the more travel that is required to fully disengage. I too did the 1" master with the standard issue 7/8" push-type slave. No problem getting the necessary amount of travel, but the Hulk would have experienced difficulty pushing the pedal. I dropped back to the 3/4" large-capacity master. My clutch is finally working well (no grinding) and pedal pressure is much lighter. I did extend the pedal rod a bit for increased travel. With over 400 Lbs of torque at the rear end, I was eating lighter-duty clutches. The current system is good.

[Ed]

According to Quartermaster the correct size master cylinder varies according to clutch type
5/8 Dia for 5/16 travel All Multi Disc Racing Clutches
3/4 Dia for 7/16 travel Borg & Beck or Long 3 finger style
7/8 Dia for 19/32travel Diaphram Style w/short throw
15/16 dia for 11/16 trevel All other Diaphram style

From this information it is evident that not all clutches are created equal
I have always used Quartermaster but they require chevrolet dimension transmittion input bearing retainer..for me the choice is t-10 machined for the larger steel gears in a GM spec aluminum case...personal preference...
I am able to use 3/4 master with a diaphram clutch...gives a very light pedal but requires adjestment for wear which requires dropping the transmittion
For those that have an external slave the suggested master cylinder sizes may not be correct but it does demonstrate that there is a difference between the Long style and the diaphram style....but the travel dimension will give the math guys something to work with

[spd4me]

Tony - you said you went to a 3/4" large capacity master. What brand is it. My setup is a Wilwood 3/4 small master with a Wilwood pull style slave (they only make one type of slave). It has grinded going into reverse since day one. I also had a machine shop make me a push rod that is 1" longer in order to get my pedal more in a up position.

[Naumoff]

How is the slave mounted?
Does it move at all or is it secured really well?
You could be loosing that 1/8" or so you need if the mount is not rigid.

[JeepSnake]

Bob, Mom & Dad's 427 car has the Wilwood pull-type cylinder, and it too has been a pain since day one. Adjustment nuts backing off, grinding going into reverse, etc. You'd think that a jam nut and red Locktite would hold the rod adjustment, but no. The laws of physics somehow are suspended around that thing. It works peachy keen for a good while - enough that you think it's fine - and then, wham, it's all out of whack.

Our mount is not very rigid, so I suspect in our case that Tony is onto the root cause of the issue.

Sorry I don't have a solution; but I am looking into the mounts that allow a push type cylinder to be mounted to the trans case and push forward on the clutch lever.

[Naumoff]

Zach, a good friend of mine has the same Wilwood puller slave on his Cobra and it just did that Sunday. The Jam nut fell off the slave rod just as we all pulled into a parking spot. We were lucky the nut and washers were right there on the ground under the car.
Three Cobras, Three tool pooches, three guys to fix it.
We stopped at a Porsche Club autoX and could of borrowed a floor jack but we didn't.
I held the rod, Billy put the nut on and Stephen was the eyes from above.

Bob,
Another thing to check is that the clutch fork is not hitting the bellhousing before it can fully disengage the clutch. You might have to put washer under the fulcrum mount to give it the clearance it needs.
We had an issue with Jim's car with that when we installed the clutch slave for his car.

[spd4me]

Tony - I had a 1/2 steel bracket made to mount slave. See attached photos. There really isn't any movement in bracket. But I will check fork and bellhousing. I thought about using a 1/4" thick piece of aliminum bar stock and drill couple holes to use as spacer between fork and bellhousing but can't get a wrench around the inside bolts. Not enough room between nut and fork. Would have to remove bellhousing which is way to much trouble.

[spd4me]

I also took a 1" dia ball bearing, heated up and let cool over night to soften and sawed in half. Heated back up and dipped in water to harden. Driled hole and used to hold slave rod in the indention in fork.

[Naumoff]

Looks pretty solid to me.

We did Jim's without even removing the trans.
Welded the nuts on the bracket inside and we used washers to space it out and welded them on too.
It ain't pretty but it worked. We did have it on a two post lift.

[Naumoff]

Not that it make a difference to disengage the clutch but why did you set it up so that the cylinder moves and not just the pull rod?

[spd4me]

That's the way it came from wilwood. The rod from the slave to fork is screwed into the slave body so it's fixed and the swivel end goes to the bracket and moves in and out. I like your bolt setup. Adding the space moves the fulcum point closer to throw out bearing reducing the angle which gives more leverage. Part of my problem may be that the fork is past 90 degree angle to trans shaft. It would be easer if angle was more like 60 degrees. How did you get nuts on inside of bellhousing loose? I may have to take a wrench and grind it down so it's thin enough to fit between housing and fork.
bob

[Naumoff]

That was easy. We had the nuts on the outside first.
Then after trying to get it back in there the same way and couldn't we came up with the welding the nut and washer spacer on the fulcrum bracket.
It was either that or pull the trans and we didn't want to do that.
It worked like a charm. There is a thread as to what we did. go to post #9

link to thread

[spd4me]

Tony- I just spent the last 45 min reading through the thread you listed and am exhausted. Can the fork be removed from the bearing and pivot while inside the bellhousing. Like I said before, their isn't enough room between fork and pivot bolts to get wrench on. If I could disconnect, I could remove pivot and put in spaced. The pic of the welded nut pivot you show - does the whole thing go inside and the two greased threaded end stick out through holes in bellhousing? A larger brake line will result in less fluid pushed into slave. The idea behind hydraulics is pressure. Small force can move larger objects. The m/c needs to create enough pressure to push clutch springs. Increasing the line size reduces the pressure so it would take more imput force (foot pressure) to move. There's a web site www.stoptech.com that explains all this. I re-routed my brake line over the top of foot box and have to order a shorter braided line to connect to slave. Hopefully I can do this week and will be happy. One draw back with the large resevoir is trying to get the stupid clamp over the top cover.
bob

[Naumoff]

Sorry about that Bob. I should have warned you that the thread got long. I only wanted to show you what we did to the pivot bracket.

To answer your question about the removal of the fork it is No.
That was the problem with trying to get the spacers in with the bolt and washer in on the bracket from the inside.
The bracket has to be removed to be able to pull the fork out of the bearing.

Do your bolt have nuts on them or is your bellhousing taped?

From what you are saying your bolts go into the bracket and through the bellhousing and the nuts are on the outside. right?

If this is the case I would cut the nuts off and then get some new ones.

Once the bolts are loose them you can pull the fork out enough to get the pivot bracket off.
With out the bracket bolts being removed the clip on the fork keeps you from pulling it out and there isn't enough play to push it in to unclip it from the pivot bracket.

The pic of the welded nut pivot you show - does the whole thing go inside and the two greased threaded end stick out through holes in bellhousing?

We bolted the nuts and washers in place then protected the exposed threads of the bolts with tape during welding.( the tape must be what you think is grease) The bolts came out and we had an equivalent to a tapped pivot bracket with spacers attached. We clipped it on the clutch fork then clipped the fork to the bearing. Then we lined up the bracket with the bolt holes and ran the bolts in from outside.