This article is one in a series that have been released in conjunction with Wayne's book, 101 Projects for Your Porsche 911. The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Porsche 911 owner's collection. See The Official Book Website for more details.
Prior to replacing your entire clutch mechanism, it is recommended that you replace the clutch cable, and eliminate it as a possible source of clutch problems. It is common for a failing cable to indicate the same symptoms as a bad or worn out clutch. A very stiff clutch pedal, or difficulty releasing the clutch may be caused by the cable binding or separating. Replacing the clutch cable and the helper spring on late 915 models (Pelican Technical Article: Replacing Your Clutch Helper Spring) may relieve more clutch problems that you would imagine. While you have access to the area, it may be a wise idea to rebuild your pedal cluster as well and replace the old plastic bushings with durable bronze ones.
Replacement of the cable is not a difficult task. Begin by removing the driver's side carpet and floormat, and unbolting the wooden foot pedal cover from the car. Underneath you will see the pedal cluster and the accelerator pedal. The clutch cable is attached to the right side of the pedal cluster using a U-shaped clevis (sometimes called a trunion pin or retaining fork), and a snap-on retainer. The retainer has a small pin that attaches the cable to the arm on the pedal cluster. Using a small screwdriver, remove this retaining pin from the U-shaped clevis. If the cable hasn't been replaced in a long time, it may require some WD-40 or a significant amount of force to remove the pin. Don't be concerned about destroying the retainer pin, as they are inexpensive and easily replaced
After you get the retaining pin removed, you should be able to unscrew the U-shaped clevis from the end of the clutch cable. If it is frozen onto the end of the cable, try a spraying a little bit of lubricant in the area. Don't be afraid to cut it off either, as you will be throwing out the old cable anyways.
Now, move under the car. You will have to elevate the car on jack stands for this procedure (see Pelican Technical Article: Jacking Up Your Car). Underneath the car, you should see the point where the clutch cable exits out of the firewall, and where it attaches to the throw-out arm on the transmission. The early 911s had a single throw-out arm that was a very simple design. Starting in 1977, 911s with the 915 transmission used a more complicated system that incorporated an omega-shaped (() spring.
Underneath the car, the cable should be attached to the transmission throw-out arm. On the early 911s, the clutch cable was inserted into a hole in a flange on the transmission, and then attached to the throw-out arm. To remove the cable, simply unscrew the two nuts on the end of the cable, and pull it through the transmission flange. On the 1977-86 911s, the cable is hooked onto a large arm connected to the helper spring, and clamped onto a flange on the transmission. If you loosen up the nuts that clamp the cable to the transmission, then it should become loose and slide right off of the hook.
Installing the new cable is straightforward. It's not necessary to lubricate the cable before you install it, but a little bit of white lithium grease can't hurt. Slide the new cable into the hole in the firewall and push it all the way back until the end of the cable is mated flush against the small tube on the firewall. Make sure that the cable is firmly seated on this tube - it may slip off later and affect your clutch adjustment.
Attach the new cable underneath the car similarly to how you removed it. Clutch adjustment is performed by altering the position of the mounting nuts, but we'll cover that in Pelican Technical Article: Clutch Adjustment. Make a best guess at where the nuts should be and hand tighten them. Make sure that you don't forget the second tightening nut on the early 911s: this prevents the clutch adjustment from coming loose later on.
Moving back into the inside of the car, re-affix the clutch cable to the pedal cluster using the clevis and the retaining pin. The trunion should be screwed onto the cable along with its locknut, and the distance from the outer face of the locknut to the end of the cable should be about 20mm or 0.8".
After you have the new cable installed, it's time to adjust the clutch. Project 11 covers this in detail.
The clutch clevis is screwed onto the end of the clutch cable, and attached to the lever arm with a snap retainer pin. Removal of the pin is not always easy, but can be accomplished with a little bit of patience. Be careful not to drop the snap retainer, as it may be difficult to fish out of the area directly below.
Shown here is the underside of the 1977-86 915 transmission. The clutch cable is attached to a long lever arm that is assisted in its travel by a horseshoe shaped helper spring. This spring gives the clutch some of its snap-in feel when it's engaged. The long lever acts on a smaller lever that is connected directly to the throw-out arm and the throw-out bearing. Backlash on the smaller arm is removed by the small coil spring that removes slack from the system.
When installing the new clutch cable, make sure that the cable is mounted securely within its fitting against the firewall. If the cable is not mated properly, then the clutch will fall out of adjustment the first time that you press on the pedal.