Slave Cylinder Clutch Setup

The Dreamer · #1 (**permalink**) 03-20-2005, 09:58 AM

I need to find out how much travel you get out of your slave cylinder. I know the Kirkhams recommend a hydraulic TO bearing, but I've heard too many horror stories about them and I'm hard headed. Anyway, I had them put in a .75 master cylinder for the clutch and I'm using a .875 (7/8") slave cylinder. I know a couple of people have said they are using this setup and Shelby uses this setup on their cars, but I'm having to preload the pressure plate to get the clutch to release. I'm only getting about .5" of travel out of the slave. This seems low to me. After numerous adjustments, I still get about the same amount of travel and we have bled this thing to death. I'm using a TKO600 and Shelby block engine.

My next step is to peek into the pedal box, but I would like to know if anyone has some ideas about what could be robbing my slave cylinder of stroke.

Specialk · #2 (**permalink**) 03-20-2005, 10:34 AM

I remember reading somewhere that a clutch only needs 3/4" or so of travel to full disengage. Are you saying yours will not disengage? I am having a similar issue with a Kirkham that is using a Shelby slave, it doesn't seem to want to disengage. I have built several Shelbys that have worked flawlessly. Just bolt all the pieces on, bleeding only took a minute or two, and they worked perfectly with no further adjustment. This one Kirkham is starting to give me heartburn!

If somebody has any ideas, I would love to hear them.

thorconstr · #3 (**permalink**) 03-20-2005, 10:41 AM

Mike Forte at Forte's Parts Connection has a nice bellhousing mounted slave setup.

Bruce Edwards · #4 (**permalink**) 03-20-2005, 11:47 AM

If the clutch arm is to long you will not get the correct movement at the bearing end. Just a thought.

RedCSX1 · #5 (**permalink**) 03-20-2005, 12:56 PM

I am running a billet slave with big block clutch arm. I have all threat. You will need to scew it out further than you think you should, Have the car on jack stands , as you adjust it out have someone in the car pressing the clutch to test it while you push on the rear wheels to see if the spin.

tpiini · #6 (**permalink**) 03-20-2005, 01:09 PM

I just went through this problem! I ended up replacing my master cylinder with a 7/8" bore. That moved the slave full-stroke, but that was only 1 1/8" and I still had to preload the T/O bearing to get full disengagement. On the advice of the manufacturer, I took the dry end off my slave and removed the return spring. That gave me all the stroke I needed. I just put a return spring on the fork instead.

My M/C and slave cyl. are both CNC Brakes units.

Hope this helps. Tom

The Dreamer · #7 (**permalink**) 03-20-2005, 05:58 PM

Thanks for the replys guys.

Bruce, what do you mean too long? I need a rod long enough to preload the pressure plate enough. The reason I ask is one thing I think may be a problem is the hole in the fork may not be large enough to allow the rod to arc and the fork moves and I may get binding from the rod sticking through the fork. Is this what you are talking about?

SpecialK, are you using a Tremec in the Kirkham. The forks are different that the Toploader and I'm thinking that has something to do with it.

Tom, my hydraulics are a little rusty, but I think the stroke should be the ratio of the areas of the bores. Even with the .75 master, I should get 73% of the master's stroke with a .875 slave. I was thinking the master's stoke was at least 1 in and if that is the case, the stoke I'm getting is still a little short.

Bruce Edwards · #8 (**permalink**) 03-20-2005, 06:02 PM

I am talking about the length of the clutch fork. If it is to long on the "Push" end it will not move far enough to release the clutch on the bearing side. Think about how a lever works. The longer the bar the more you have to move it before much movement is seen on the other end. The shorter the bar the more movement and the more pressure needed to move it.
Does that help?

tpiini · #9 (**permalink**) 03-20-2005, 06:03 PM

Right. So if you increase the M/C bore, you increase the slave stroke with the same M/C travel. My problem was that because of the length of my fork, I needed about 1 1/4" of slave movement to move my T/O bearing enough.

Bruce Edwards · #10 (**permalink**) 03-20-2005, 06:09 PM

You got it! If you used a shorter fork you would not need to move it as far with the slave. Trade off is a harder pedal but most folks will not see that much of a change in pressure.

The Dreamer · #11 (**permalink**) 03-20-2005, 06:28 PM

Oh, does Tremec make different lenght clutch fork or are you saying drill the fork closer in? I don't think either one would work because the angle of the rod would be further off alignment with the slave cylinder.

Bruce Edwards · #12 (**permalink**) 03-20-2005, 06:45 PM

Question. Were is the pivot? The Tremic is set up for a cable "pull" system not a linkage push set up. If you are using an early model fork with a pivot on the slave side, pushing from the engine side like the picture shown above , than yes they are different in length. If the rod is off center now that is not good to start with. For the best set up the push rod needs to push very close to straight on or it can bind the piston in the slave bore or cause the rod to rub the inside of the bore.
If you take a look at the picture above you can see the rod is nice and straight. The only problem or thing that may be a problem down the road is the slave looks a bit on the short side. If the system is set up correctly the bearing should not contact the clutch fingers. The early style bearings do not do well if they ride on the fingers.
Isn't setting up kit cars fun!!!

The Dreamer · #13 (**permalink**) 03-22-2005, 05:25 AM

My slave lines up initially, but as the fork pivots, the end moves in an arc. I think I'm getting binding as the fork travels in the arc. I have a Lakewood bellhousing, so I'm using the same pivot as the big block forks use, only I have the fork for a Tremec.

My set up is a little different than most Kirkhams because I'm using the TKO600 and from what I can tell, I'm one of the first to actually get it running. My pressure plate (12 in) is different than the Toploader big input pressure plates and that may affect how much travel is needed to release the clutch. I know I'm close, but as the clutch gets heat into it, shifts become harder.

I'm first going to try to find a .75 Lockheed-Wagner slave and if I can't find a smaller bore slave, I will swap out the master for a CNC .875 bore.

trularin · #14 (**permalink**) 03-22-2005, 07:46 AM

As long as the slave has the travel available, you can change the master to increase or decrease the proportional travel.

Suppose you have a .5 inch slave and a .5 master, the travel of the master is equal to the travel of the slave. So, if you increase the size of the piston in the master, you increase the travel of the slave. It is a matter of volumes. The trade off is force. By increasing the diameter of the master, you increase the amount of force necessary to move the slave.

This makes using interchangable master cylinders very appealing, like Tilton.

Hope this helps.

coyled · #15 (**permalink**) 03-22-2005, 07:56 AM

I went through this one a few years ago. I had to put a spacer between the bell housing and the clutch fork pivot to get the correct lever ratio going. Washers will work and it will change the leverage so that the throw out bearing moves further. Good luck, Scott.

Morris · #16 (**permalink**) 03-22-2005, 08:24 AM

Volumn = Surface Area X Stroke

Volumn = Pie/4 X (Cyl) Sq'd X Stroke

Volumn = 3.14/4 X (.750)SQ'd X 1"

This is for a 3/4" Master Cyl moving 1" stroke...

Then take this volumn and compare it to changes you make to the master cyl or stroke in the calculation ....

Hope this helps

Morris

The Dreamer · #17 (**permalink**) 03-22-2005, 10:57 AM

Well, I just discovered that I don't have a .875 in bore slave, but a 1 in bore slave. Ahhhhh, that's the problem. Given that, I'm getting the right amount of stroke out of the slave (56% of the master's stroke).

Coyled, I wish I had thought of the washer trick before I put in the transmission. I'm so close that might have worked for me.

Morris, thanks for the calculations. That confirms my rusty hydraulics (mentioned earlier) that the stroke is the ratio of the areas.

Now, does anyone know where to get a .75 in bore Lockheed-Wagner slave cylinder (or one that mounts like it)?

coyled · #18 (**permalink**) 03-22-2005, 11:23 AM

You can insert the washers with out pulling the tranny. It does require some slight of hand. Scott

trularin · #19 (**permalink**) 03-22-2005, 11:24 AM

Does it look like a Tilton???

Pegasus Racing.

David Kirkham · #20 (**permalink**) 04-28-2005, 06:07 PM

Morris,

On my new minature bell housing idea, what do you think about putting the throw out bearing on the bellhousing instead of the transmission?

That way everything can be checked without having to install the transmission.

Also, my new car will have a removeable transmission tunnel top. I recommend you do it as well. Probably a must for any race type car that will be tinkered with.

David