"Pull" Clutches and Their Works in 2.2 Enginesby Roger Chaney, Technical Editor
History and a little philosophy (mine). Is design change always an improvement, even when the result is an easier operating mechanism? The answer is not always easy to come by and must be the result of experience in the field by the owner/operator, the mechanics (s) when the part or assembly needs maintenance, and how often it needs maintenance. |
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| Some owners of ‘70 Porsches and their dealers would vote for tradition if given a choice on clutches. Porsche revised their new design soon after ‘70 models hit the streets because dealers soon discovered that when a clutch disc went bad on this new "backward” clutch, it was next to impossible to separate the transmission to replace the parts. | ||
| Operation. By looking at the diagrams, you can follow through from the clutch pedal to see how this new system works. Follow the half arrows. | ||
| Before 1970, the cable did the work of operating the throw-out fork directly, with the cable sleeve or cable conduit being only a guide. The 1970 design calls for a fix cable at the rear of the differential housing. When the pedal is depressed, the cable is forced to straighten. In the process, the cable sleeve must straighten too, but it is restrained where the cable enters the tunnel. In order to straighten, the sleeve must move rearward at the transmission. Now look at the clutch diagram. | ||
| As the sleeve moves back, the fork must go too, so that the throw-out bearing is forced forward pulling the diaphragm spring with it. With spring load removed from the pressure plate, built in leaf type springs push the plate away from the disc so there is no drag and release is positive. | ||
| Adjustments. Clutch adjustment with this system is a bit different and there is more to check than before, but the end result is the same—to get correct preload of the throw-out bearing (pedal freeplay) and correct travel limit for the diaphragm spring. Freeplay is adjusted by loosening the locknut and turning the adjusting nut at the clutch fork fitting front end. Turn the nut until clutch pedal freeplay (pull pedal to the rear and release) is 20-25 mm (0.8-1.0”) when measured about center of the foot pad. | ||
| This adjustment will shrink as the clutch disc wears and the throw-out fork will eventually move forward far enough to hit the clutch housing. The earliest 1970 cars had no way to correct for this, but this was soon changed by installing an adjustable clutch fork (see Diagram B). | ||
| If the fork is found to rest very close to the front of the housing hole through which it protrudes, a flashlight and long shank screwdriver can be used to readjust the fork position. The cable and sleeve should be disconnected so free access can be made for fork adjustment. Shop data say that fork-to-rear-of-gearbox-housing distance should be 83 mm (about 31/4") with light rear load on fork. |  |
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| Clutch pedal stop (clutch travel limit) adjustment should be made as on earlier Porsche cars. The air here is to not over-travel the diaphragm spring when disengaging the clutch. Check for travel by idling the engine (after running to warm up transmission), gearshift in neutral, clutch pedal up. Now carefully push the shift lever as if you were going into reverse until you just hear the reverse gears hitting each other. Depress the pedal slowly until the gears stop turning, then note how much farther the pedal must go to hit the stop. If this distance at the pedal is more than 1/2" readjust the stop downward. If you are won- dering, the stop is under the floor mat and the clamp screws (2) are made for a 4 mm Allen type wrench (hex key). Shop instructions say that the pedal stop is correct when total travel at the fork cable attachment is 15 mm. I believe that the “gear noise” method will give a more usable setting. | ||
| This newest clutch system has another point which must be watched closely
before and after any adjustments are made. This is the cable guide clip and the relation
of the cable to it with pedal relaxed and with pedal to the stop. The cable must not be
free of the clip top at related pedal or bottomed at or before pedal hits the floor stop.
If either case is seen, the cable length must be changed at the pedal lever fitting at the
floor tunnel forward end. Porsche has supplied an access hole in the tunnel top under the
carpet on 1970 and 1971 911’s for this job. You may also need to remove the left
floor board half. 1/72
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