Issue with clutch slave cylinder pushing clutch fork to far

[Colin Fabri]

I have an issue with a new installation, where pushing the clutch all the way causes the slave cylinder to push the end of the fork onto the back of the spinning clutch. This happens right at the end of the travel and the clutch works fine if I do not press all the way down. I have tried adjusting at the pedal end however it did not make any difference.

Gearbox is G50-01 with Porsche slave cylinder. Pedal box is Tilton on a RCR40 chassis. Master cylinder and Tilton pedals were provided as part of RCR kit.

One thought would be to create a pedal stop, however I have not read of anyone else needing to do this.

Any ideas on how to limit the travel of the slave cylinder?

Thanks
Colin

 

[flatchat(Chris)]

Hi Col , a smaller dia master cyl. or, the tilton pedal has provision for a stop --5/16" unf I think

 

[Terry Oxandale]

A pedal stop would be one option. Another would be a slightly smaller master cylinder, but at the sizes being used, you wouldn't want to go too small. If you have a 3/4" MC (which I think is Fran's supplied size), then you may be able to use Tilton's 7/10" MC which is 87% the volume push of the 3/4" MC, which will provide that much less stroke at the SC, and it will ease up the pedal pressure.

 

[Bill Musarra]

Colin,
The advice of the others is one way to correct the problem. Some other options are to look at the fork and see if for some reason it may be bent causing it to be going in further than supposed to. If this shows nothing then a pedal stop is the next best thing. You can accomplish this one of several ways.
The first is to make measurements of the travel of the pedal vs. the travel of the fork or throwout bearing. This can be figured out with the rear wheels off the ground. Set the trans in gear and slowly press the clutch pedal in til you can rotate the tires by hand. this is your ideal travel for the pedal. To limit the travel of the pedal you can then adjust the position of the pedal forward(less travel) or backward(more travel) from its resting position on the master cylinder, by screwing the push rod further in or out of the pedal. By moving it further in, you will be extending your leg further to get it to disengage. Or if you prefer set the ideal distance, to hit the front firewall, if you have the MC mounted on the other side of the wall. If you like the position of the pedal as it is , then build out the firewall to meet the pedal at the desired travel point.
If the MC is on the same side as the pedal, fabricate a cylinder to fit over the push rod that will limit the travel of the pedal forward. Put a nut on either end to stabilize the cylinder. You could also make a stop for the pedal by welding a piece of stock to the mounting surface of the MC to stop the travel of the pedal. Then you could use the screw of the push rod to make up for any wear of the clutch.
If the threaded portion of the rod goes through the mounting bracket of the MC, you could use a double nut with lockwasher in between, to set(limit) the travel of the push rod. Not knowing your setup, one of these should help.

Bill

 

[Robert May Eng.]

As above but before you do anything check the position of the piston in the slave. If its to far down the bore to start with you may need to change the length of the push rod . From the static position see how far you can push the slave back home, be mindfull that excess fluid will spill from the master.

Bob

 

[Bill Musarra]

I think the right question is which slave do you have, and what is the bore/stroke of the piston/cylinder. You have to have the proper slave to work with the MC. If not then the piston will not go far enough to release the clutch, or it will go too far, and thus the problem. Which is what I think you have. The ratio of the two forks will not change regardless of any adjustment, the ratio remains the same, and I don't believe you will ever get it to work with that solution. Again, you have two solutions. One is the pedal stop mentioned above. The other is to add some thickness to the mount of the slave(assuming your slave works like mine. See below). This will in effect lessen the throw of the slave. When you do this, then the adjustment for the clutch can be set, or the second fork can be set one notch closer to the first fork if the adjustment is too much.Don't know if this will help out but here is my setup. What we need is a pic of yours. Then we can be exact.
My setup is on a 930 with 3/4 MC and a 996 Porsche slave.

The second fork sits on top of the first fork at the pivot and rotates the shaft that moves the internal fork and the throw out bearing.

Hope this helps.

Bill

 

[Colin Fabri]

Great response. Thanks to you all, I now have lots of options to investigate.

-Col