Help Please 930 Hydraulic conversion

I have the 930. My Porsche shop foreman told me that a cooler and spray bar isn't really needed. Most of the race cars don't bother to use them. If they do the cooler is usually the one supplied by Porsche. Because the temps in the rear clip can get rather of hot, I wanted an oil cooler to the rear vent area of my 40.

Since I did that, the other bay looked out of balance.
So I added a cooler to the trans.

Then, we struggled with where do we put the return line. The only real option was to use the old drain plug. Routing it there, the gears wouldn't get the same treatment as the ring gear, With that, we decided to add the spray bar and besides, it looked kinda cool. Here is the meat of the system, pump, filter, thermostat, and the spray bar system. The lines go to 2nd, 3rd, 4th gears(see the first photo), and the ring and pinion.

Here is how we hooked up the once fill hole, now the drain plug

With mine, I decided to go with the conventional slave(pusher) and it worked out nicely. The amount of travel required is a little touchy on these setups. It is a balance between length of throw,slave/master cylinder sizing and how hard and far do you want to push.

I know this post is 4 yrs old but I noticed your setup and it appears that your starter mounts on the engine side of the bellhousing..probably using an OEM style or mini starter.
Did you modify an existing bellhousing? The clutch setup has been a drawback for me with the Porsche units because of small size and cost and it seems you have solved that problem.
I think the porsche units are really good...especially G50 and 930 boxes, I just never liked the adapter/clutch setup used on a V-8.
I recently modified a small bellhousing for a 2 liter ford by cutting it down at the trans side, adding a plate, and drilling for the new trans...I am guessing this is what you did.
Hi Bill,

I like the way you done with the slave cylinder. What sizes are you using on master and slave cylinder?

I think it is .75 Tilton master. The slave is a 996 uniit. We had to weld a base plate to mount it in the correct position. You might want to look at some of the ones that used adapter plates. Mine probably could have been done with an adapter, but I guess the mechanic thought welding the base plate was the way to go?? It is all about the angles and where the long rod meets the small rod. Confusing I know. Will send you some pics I took when I connected everything. The pixs will explain everything. I will look when i get home tonight, if I can get home. We are expedcting an inch or two of snow and ice. Terrible for Georgia. Its all the hills that make it bad.

Thanks Bill, I would really appreciate some pictures. If you know the travel distance of the slave cylinder that would be very appreciated.

BTW - also a lot of snowing here however thats more normal I guess than Georgia. We are also allowed to run studded tires which make it more safe and my Dodge Journey is great in wintertime.


Terry Oxandale

Skinny Man
I created a simple aluminum bracket that bolts onto the KEP adapter plate, using the bellhousing bolt to hold it in place. A Mitsubishi slave cylinder (approximately 18mm in diameter) operates the OEM arm using the 3/4" master cylinder (I wanted a common-application slave in case I needed to replace it). Pedal pressure is firm, bleeding hole is at the top of the bore, and it removes easily without removing the hose during engine/trans removal, and provides a bit over 30mm of travel (about the max that I can get out of the pedal assembly). Depending on your header/cross-brace configuration, you may not have enough room (or cool air) to use this configuration.

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Here is the info you asked for. The first is the slave which is a 993 or 996.


You can see the mounting bracket on my setup. Using the Porsche arms, there really was no place to put the slave. Here are the 4 ports(blue) for the spray bar. Don't remember if you were interested in this or not.

Next is the layout of the forks. The long bar rotates freely around the shaft that goes down to the fork and throw out bearing. The secondary fork sits on top of the long arm and extends over to and contacts the long rod at the adjustment screw. It is all about geometry and ratios

This is the play for the clutch pedal. It is placed touching the adjustment screw without any pressure on it. Any pressure other than the resting pressure of the slave cylinder will keep the TO bearing in contact with the pressure plate and wear it out prematurely. The spring in the pix below, was one of the stop gap things i was using to try and get enough throw from the long arm(read slave extension) in order to get the clutch to release. It was a real struggle til I got the formula. That is, the slave has to be COMPLETLY retracted in its housing before the short arm is installed(the arm is on a gear, and one notch is too much to be off by). The top of the short arm is held in place by a C clip which is missing in the photo. the spring was done away with. I believe it is in the porsche shop manual but isn't needed.


Even this is too much. I had to use a C clamp to get it far enough back.

Clutch at rest.

Clutch depressed.

My memory is failing me as I don't remember the throw distance. However it is easily figured out. Have someone there to help if possible once you have your slave and master installed and plumed, and are ready to set everything. Have the car off the ground and the trans in neutral. Have your assistant mash the pedal about half way to the firewall. Try to turn the tire by hand. If it doesn't have the assistant press a little further and try again. Continue this until a,) the tire turns, or b.) the pedal hits the firewall.
Try and measure the distance that the master will go before hitting the bottom of the cylinder. If b occurs, and you are not at the bottom of the Master cylinder, you will have to move your pedal box back a bit to get more throw, If you are at the bottom of the Master cylinder, and no release, you will have to go to a larger MC. When you reach the point where the tire turns, set the stop bolt on the clutch pedal to keep it from opening the clutch any further. The reason for this is that the fingers of the pressure plate are already being pushed in. You will notice this as you install the throw out beating into the fingers of the pressure plate. The bearing will just fall out of the fingers while the pressure plate is off the engine(fingers are convex). As you tighten the bolts the fingers will start moving into the pressure plate(concave) and will grip the throw out bearing and creates pressure on the clutch(engagement). If you continue to press on the TO bearing beyond where the clutch releases, it will bend the fingers of the pressure plate(not good), and eventually the TO bearing will fall off the fingers and go inside the pressure plate itself. So be sure to set the pedal stop just beyond where the clutch releases.
Here are a coupleof pixs for reference. the pressure plate is a Kennedy item.


So as to not make this a long diatribe, let me know when you are ready to install the trans. I can give you some pointers that will save you some time.
Hope this helps.

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Hi Bill,

Big thanks for your very thourogh explanation. This will be very helpful for me when I will rebuild the slave mechanism on my tranny. Until now I have used a pulling slave cylinder but the setup gives a very hard pedal to pressure.

Once more - many thanks!!!
I just dicovered that I gave you some bad info. When I said the car should be "off the ground and in neutral". I should have said the gearbox needs to be in 1st or 2nd gear. The wheels inability to turn is an indication the clutch has not released and to mash the pedal further. Once the clutch releases, the tire will turn.
Sorry about that.


Ron Earp

GBox has a conversion. I used it on my Lola T70 Spyder replica with 930. Worked great and we raced with it as well - no failures. It doesn't require monkeying around with parts either, bolt on their arm and piston style slave and go. Probably find some pictures of it in my old build thread.