930 slave cylinder help

[Bill Musarra]

In testing the clutch on my car I am not able to get the clutch to release and go into gear. I have the KEP setup and a porsche slave(was told the number but have since forgotten, think it is a 96?). The master is a Tilton 1" unit. The throwout bearing has ears on the top and bottom and they are about 2" away from the pressure plate(orientation).
Bleeding is easy and no problem. When I mash the clutch, it is very stiff. The arm of the slave only moves about a half inch or so and I am reluctant to push harder for fear of breaking/bending, or causing some other problem. I have partially pulled the trans away from the adapter. Looking into the window I can make out the arms of the fork and I would assume the throwout bearing. It appears the fork goes in front of the "ears" on the bearing(the side between the ears and the pressure plate. I am reluctant to pull the trans all the way out because I have heard there is a trick to getting it all back together. With the engine in the car and all the wiring harness pieces running across the top of the trans, it becomes that much harder to mount.
When the trans was mated to the engine I wasn't there and the mechanic had never mated one. I had him talk to the shop foreman of Jim Ellis Porsche here in Atlanta. The mechanic is a very knowledgeable one who works on mostly American cars and is an avid drag racer. He routinely builds 7 liter fords with single and dual turbos, so he knows his way around a car. They are the ones who installed the FAST ignition and FI controller and final torques of the engine.
He(a country boy) didn't like the attitude of the foreman and proceeded to mount the trans. So I don't know if he "missed a step".
I am including some pics of the slave for reference.

I have the short fork(930 part) placed on just for reference. I removed it so as to pull the trans away enough to see how the mechanism worked.

I need some advice from those with experience, as I have about zero. Am I correct about the fork placement and the throwout bearing? Is the master about the right size? What is the distance that the mechanism should travel? Should a "stop" be placed on the Tilton pedal to limit travel, and if so how much is acceptable?

Bill

 

[Bill Musarra]

My shop foreman finally got back to me, and I have checked the arm TOB relationship and they are correct. Now all I have to do is get the correct master cylinder for this setup. The foreman gave me the size of the master cylinder. It measures 22 mm compared to the 25 that I have now. This is obviously too big considering that for every inch the master travels the slave will travel 1.3 inches if my math is correct. The TOB only needs to move 1/2 to 3/4 inches to get full release. The length of the arm on the slave is 4 inches. The Tilton pedals I have are billed as 5.5 :1. Now, all I need is a refresher course on the math that leads me to the nearest size master cylinder for this unit. I understand the general idea that a smaller Master cylinder exerts more pressure with a longer travel.If it is a ratio and proportion set up then a 3/4 inch unit would, for 1 inch of travel, move the slave .725 inches and a 5/8 Mc would move the slave .5 inches. Am I heading in the right direction. I am sure there is a formula that will get me close. Anyone got the formula handy?? Or better still, give me an idea of what I need.
There are several on ebay and with the rebuild kits I could come out cheap on them.

Bill

 

[Russ Noble]

The foreman gave me the size of the master cylinder. It measures 22 mm compared to the 25 that I have now. This is obviously too big considering that for every inch the master travels the slave will travel 1.3 inches if my math is correct. The TOB only needs to move 1/2 to 3/4 inches to get full release.

If it is a ratio and proportion set up then a 3/4 inch unit would, for 1 inch of travel, move the slave .725 inches and a 5/8 Mc would move the slave .5 inches. Am I heading in the right direction. I am sure there is a formula that will get me close. Anyone got the formula handy?? Or better still, give me an idea of what I need.
There are several on ebay and with the rebuild kits I could come out cheap on them.

Bill

Bill those figures seem consistent but no where have you told us your slave cyl diameter!

As you know I am not familiar with Porsche clutches, but since no one else has jumped into the void to help you I will say this, I think a TOB movement of 1/2 to 3/4 inch is way over the top. I think you should only need about half that. If I'm wrong about Porsche clutches, I'm sure someone will rapidly shoot me down!

With your 4" (100mm) slave arm you will be getting 60% movement at the TOB, (the pivot of these arms is situated about 60mm off the centreline of the trans) therefore 1" movement at the slave arm will give you .6" at the TOB. I think you only need half of that ie .5" at the slave, so according to your figures the 5/8" cylinder will be the bees knees.

Incidentally I am using a 5/8 master on my setup and it works nicely, (drove it today for the first time!) but that is with a hydraulic TOB and 7.25" triple plate, so not really relevant to your situation.

And if you care to do the calculations you will realise that your 1" master cylinder will take approx 2.5 times more effort to depress than the 5/8.This will be almost impossible to do. And that seems to be your problem!

Hope some of that helps.

 

[Jac Mac]

[QUOTE = Russ Noble]

(drove it today for the first time!) [/QUOTE]...................





Bill, if you were to move the arm manually until the plate releases, then measure that amount of movement required to do so, then compute the amount of mastercyl travel reqd to move the slave cyl by this amount plus a bit for line expansion etc you should be able to come up with the reqd master cyl size. Like Russ I am not conversant with lever ratios in P*** car stuff & that appears to be one of the 'pull to release type' bearing setups.

Russ Noble....... words fail me,.... how can you drop out seven words like that in the middle of another thread when you KNOW most of the regular forum members have been crossing every appendage they have as they wait for word of your first drive......

 

[Russ Noble]

Russ Noble....... words fail me,.... how can you drop out seven words like that in the middle of another thread when you KNOW most of the regular forum members have been crossing every appendage they have as they wait for word of your first drive......

Jac Mac, I know you just love 'crossing your appendage'. So I thought you wouldn't mind doing it for a bit longer whilst I dealt with Bill's query first. See my build log for todays details.

 

[Dave Deerson]

Bill,
Jac Mac has a point in trying to release the clutch at the arm directly. But do make sure it does release at all as when I put my car( Chevy LS6 with 930 'box and KEP adapter) back together this spring, I could not get the arm to move past a certain point(just a little bit and then would feel things flexing) and noticed that as the trans was assembled onto the mid-plate and input shaft, the release bearing would rotate just slightly as the release arm made engagement and would bind up if I tried to move the arm to disengage.
Get under the car and look into the access hole now on the bottom of the bellhousing with an inspection light to verify that the release arm is not bound in the "ears". As I was installing the trans I would jiggle the release shaft to keep the bearing and arm from going into bind. Not sure if this is what is going on with your car, but just wanted to share a condition i had with a similar set up.

Good luck,
Dave D.