915 clutch pull to push
If you read my last post - 'Hydraulic clutch slave' which was about fitting a hydraulic clutch to a Porsche 915 gearbox you might have thought that it was a good solution to an otherwise difficult issue to solve. Well that is what I thought until I tried to fit everything together. What I actually found was that the slave cylinder that I used was too long and meant that it fouled on the clutch assembly when the engine was installed in the gearbox. With limited time to buy and fit another shorter unit I decided to look at converting the old pull style 915 clutch release to a traditional push style.
When using a 911 style clutch assembly the installation of the cable and release mechanism is pretty simple. The release arm is located at the bottom of the box instead of at the top like on a VW, and apart from making an adaptor to hook the cable to the arm, the clutch cable lines right up and the install is pretty simple.
However, the 915 gearbox release operation is pretty much the exact opposite to what you normally find on a VW box. The 915 style arm pulls the release bearing away from the engine to disengage it instead of pushing it. This means that to get the arm to work in the opposite direction you need to do some small modifications.
What you basically need to do is swap the release arm around about 270 degrees on the shaft so that you pull it from the opposite side of the engine. This will then push the release arm instead of pulling it. To make this work you need to both modify the release shaft as well as make up a mounting for the clutch bowden tube.
After removing the release arm, pivot shaft and release fork you will need to machine a groove in the pivot shaft to allow the release fork to be mounted upside down. After you have done this reassemble the shaft along with the release arm and release fork.
You will need to wire the stock style VW release bearing onto the release fork as it will not safely clip into position. Make sure you go around a couple of times but don't forget to leave enough slack for the bearing to pivot back and forth. I Also had to mod the input shaft tube to accept the smaller VW release bearing. Even though it was a nice tight press fit I welded this into place to prevent it from moving.
Next up is the bracket for the bowden tube. I simply welded some scrap bits of steel together until I had made something that held the cable in position as required.
The last part was the release arm itself. To join the cable to the release arm I made up a simple tube through which the clutch cable would pass. This tube was fixed to the release arm via a stud which passes through the bearings on the end where the Omega spring goes which is no longer needed with the clutch in this configuration.
Finally everything was installed on the car.
A point to note was that I had already previously extended the clutch pedal release arm (the bit that the clutch cable hooks on to.) I did this so that the VW setup would work with the 915 clutch and box.
So with everything in place the only thing really left to do is put it all together and try it...