Broken 911SC clutch cable: autopsy

[Brian Kolner]

Greetings. I have a tale of woe and intrigue regarding clutch cables in my 1979 911SC that I would like to share in the hopes that it may save someone an early failure. During the recent deluge in California, I was leaving a gas station, at night, on Highway 80 (between Sacramento and the Bay Area) when I pressed the clutch in to go from first to neutral and the pedal snapped down to the floor board. Fortunately I was close enough to the pumps that with a little help we got the car pushed back under the awning above the pumps and it could stay out of the rain. Five hours later I had the car back at home (but not in the garage, that's a different story). The following day I discovered that the clutch cable had broken and was slightly annoyed since I had put a new one in six years ago. I have since learned that I got quite decent life out of it, but nevertheless, I wanted to know why it failed. Below is a photo of the cable with the plastic covering removed on either side of the break adjacent to the metal guide tube. You can see that there is corrosion at the point where the cable hits the bend in the tube. Notice that the spiral plastic (large OD) tubing coming out of the guide tube is bunched up. Not a pretty connection, is it? I surmise that this junction, which should keep out the elements, allowed water to seep into the guide tube where it rested at the lowest point which is regrettably where the cable is pulled against the bend in the tube.

I purchased a new cable (930.423.401.05) which is noticeably beefier. The actual cable OD (as opposed to the plastic jacketing) is 0.162” for the new one versus 0.139” for the old one. This suggests that Porsche (or their vendor) has improved the design. The construction quality is noticeably better but as an added bit of insurance, I smeared a layer of RTV (GE Silicone Rubber) around the suspect joint to seal it against any water that might seep in and, on top of that, I put a piece of 3/4” heat shrink tubing around the joint after it had cured. You can see this in the second photo below. It could probably been a few inches longer but that was the only piece I had on hand. I think that the combination should prevent any water from getting into that area of the bottom of the guide tube now.

Since I didn't have the luxury of waiting for a parts shipment, I had to source the cable from my local Porsche shop and while waiting for the RTV to set I checked the part number and price at Pelican and other distributors. I discovered that Porsche has superseded this part to 930.423.401.09. This probably occurred within the last year or so since the shop I get my parts from is pretty up-to-date. If anyone knows exactly how this new cable (.09) differs from the last version (.05), please share.

I hope someone finds this informative.

-Brian