914 –with 930 trans?, Hydraulic clutch? Options

[burton73]

As the new car that I have coming to me does not have the master cylinder for the 930 box I called Easy wrecking and went over my options of putting a G-50 Clutch and brake assembly in. They have one for $250. but they think there will be a lot of work to modify it to fit and may not be the best bet. They said Tilton has some Hydraulic clutch set ups. I would like to know of some ideas that you guys may have for the setting up of the Hydraulic clutch on my 930 trans that has dropped some LSD.

Thanks,

Bob

[Larry.Hubby]

Sorry for the delay in answering your questions, the holiday intervened.

This is a diagram of the cavity for the steering rack and brake master cylinder seen from the passenger side:



The brake MC is mounted on a specially stamped protrusion in the lower firewall, and is positioned with the front end down at about 11°. Presumably, this is to ensure that no air bubbles get trapped inside when the system is charged with fluid. We’re going to mount the MC for the clutch beside the brake MC, but closer to the passenger side. This means that it will have to mount to the more steeply-sloped part of the firewall, and we’ll need to position it at a downward angle, like the brake MC, for a similar reason. The situation we want to end up with looks like this:



The adaptor required has to mount the clutch MC to the 36° part of the wall, yet leave the MC at an 11° angle, hence a 25° wedge angle is needed in this part. The drawing of the part I made for this is shown below:



This part could be made simpler. It’s not necessary for the outside to be shaped like the gasket and mounting flange of the MC itself, but there are some nearby things that you will have to clear, such as the brake line to the rear of the car. Also, you could tap the mounting holes straight through (or drill a straight clearance hole and use a through bolt), but in that case you’d need to make some wedged washers or some such thing to go under the nuts or bolt heads on the inside of the firewall to deal with the fact that the bolts would be at 25° to the sheet metal.

The black parts you asked about in the photo of the area around the clutch shaft are the braces shown on the second diagram. I added these in an attempt to reduce possible metal fatigue in the area due to repeated flexing from the force of operating the clutch. After getting it all together, however, I’m not sure these are required, as there seems to be very little flexing even with them unbolted. They’re black in the photo because I made them out of aluminum and had them black anodized, like the adaptor, but you could equally well make them from sheet metal, if you use them at all.

Once you have the adaptor, you need to know where to mount it. This diagram should help with that:



The exact location isn’t terribly critical. If it’s off by a bit in either direction, or in angle, it won’t matter much. There is enough flexibility in the push rod linkage to accommodate some misalignment. A clevis is used in the original 944 application to link the push rod to the clutch pedal. I used a standard 8mm rod end with female threads instead because I wanted to be sure I had as much flexibility as possible to accommodate possible relative miss-location of the clutch shaft and the clutch MC. The rod end will screw right onto the stock push rod, no modifications necessary.

The only other thing you need is some form of extended clutch release shaft. I made a new one, following the general design practice of the factory. In the 911 models that use the 915 transmission, the factory extended and lengthened this shaft like we need to. The way that worked is that the shaft is longer, with a longer lever welded to the end, and the way the fact that the shaft is now longer than the bearing tube is handled is with a plastic spacer that goes onto the shaft before it’s inserted into the bearing tube and fills up the extra space. If my description is confusing, have a look at this diagram from PET. The clutch release shaft is 11, the spacer is 34, and the bearing tube is 9:



The only reason the shaft needed to be extended in the 911 case, is that the longer arm would otherwise interfere with the throttle linkage right above it. In our case, we have that problem, plus the fact that we need to align with the clutch MC, which is mounted to the right. The drawings for the parts I made are show below:



If this is too much machine work for your situation, you could possibly make an extension that bolts or welds onto the stock 914 shaft. Just remember that the offset to the right has to happen no further toward the end of the arm than the stock 914 arm length to avoid interfering with the throttle. If you did it this way, no spacer would be needed.

If you make a custom shaft, as I did, you have to align the arm to the shaft with the hole for the roll pin that secures the shaft to the pedal in the right angular position relative to the arm. The same relative orientation as the stock 914 works fine for this arrangement. An easy way to do this is to pin the roll pin holes of both the new shaft and the stock 914 shaft together with a single straight pin (a long 6mm bolt works well), put the arm on the shaft and turn it to be parallel to the 914 arm, mark it, then later use the marks to align the arm and weld it solid. Once again, it doesn’t have to be super accurate – off a degree or two won’t matter.



Good luck if you decide to go this way.