Care and Feeding of the Porsche Clutch
by Paul Lighthill
A recent call inquired about severe clutch chatter in a Carrera 2 that had only 30,000 miles on the odometer. It has been my experience during forty years of dealing with things mechanical that the operator is the single most important factor in determining a machines longevity and reliability. Perhaps nowhere is this more apparent than in the clutches and transmissions of our favorite cars, where PIO, or pilot-induced-oscillation as airline types call it, can shorten the life of these components to less than half of their design life.
From the first car to bear the distinguished name of Porsche to the very latest, the engineers at Gm�nd, Stuttgart, and Weisach have been in a major battle with weight. One hundred pounds of weight removed from a car is roughly equal to adding six horsepower, and furthermore, removing weight can reduce, not add costs, as increasing horsepower usually does.
Consequently, while Porsche has so far studiously avoided adopting the Lotus school of design (which states that if something doesn't break occasionally then it must be too heavy), they have gone to great lengths to ensure that the weight of their cars and the component parts is no more than is necessary for the intended purpose. This, of course, explains why Porsche cars have always excelled in performance and efficiency. It also explains why driver technique can be such a decisive factor in the longevity of components such as the clutch and transmission, since there is little excess material to allow for abuse or neglect.
For example, one late-model 911 experienced clutch failure at less than thirty thousand miles. An identical 911, but with a different owner, saw the clutch reach one hundred thousand miles. I just replaced a clutch in a 924S that had gone over 150,000 miles. If you would prefer that your clutch (and transmission) last a little longer, there are certain techniques that, once made habit, will serve to greatly prolong the life of these major (and costly) parts of your Porsche.
1. Avoid slipping the clutch whenever you start out from rest or when you change gears up or down. Of course some slipping is necessary when starting out, but if you watch the tach you will see that its possible to make entirely satisfactory starts using less than 2000 RPM. Less RPM equals less slippage. A good exercise is to stop your car on level ground, engage first gear, and then move off without using any throttle at all. This will help you find and memorize the friction point, or place in the clutch pedal travel where the clutch begins to engage. Its important to memorize the friction point for your car because if you cannot locate it quickly you are likely to slip the clutch and cause excessive wear.
When you shift up, let the clutch out smartly and don't open the throttle fully until the clutch is completely engaged. Coming in with too much throttle before the clutch is engaged will also cause slipping. When downshifting, mastering the double-clutch technique so that engine speed is matched to the speed of the rear wheels for the gear you are downshifting to will also prolong clutch life significantly. Double-clutching technique is thoroughly covered both in high performance driving schools as well as in racing textbooks. Drivers who practice it religiously on the street find that it becomes second nature and helps them achieve greater smoothness on both road and track.
2. Whenever you are stopped for a traffic light, throw the gear lever into neutral and let the clutch pedal out. Even though you may miss a second or two by having to put the pedal down and engage first gear when the light turns green, you will save much wear on both the clutch disc and release bearing. If you are uncomfortable about that semi waiting behind you, just watch the opposing light and go into first gear when you see it change to yellow. Any time you touch the clutch pedal, the internal parts of the clutch are wearing against each other, even if the pedal is all the way down. You would not want to rest your foot on the clutch pedal while driving, even lightly, for the same reason. The only condition under which the clutch will not wear is when the pedal is completely out and untouched. The same holds true for the shift lever; even the slight pressure of a resting hand is enough to cause wear on the shift forks inside the transmission, especially when multiplied over thousands of miles of driving.
3. Keep the clutch in proper adjustment(it should be checked at each routine service; see your owners manual for details). In some cases, particularly the last of the cable operated 911s (1975-86), correct adjustment is a rather involved procedure which requires adherence to the factory workshop manual and the correct setting of three adjustments. Even with the simpler 914s and earlier 911s there is a correct procedure and at least two adjustments that should be checked. Contrary to popular belief, the hydraulic clutches used by Porsche are also adjustable, and in one case that I am aware of with a 968, failure to check the adjustment led to damage that forced a transmission rebuild.
Once mastered, proper clutch technique is largely a matter of habit. You may wish to have a friend ride with you and observe your clutch habits. Or, simply try some commentary driving: describe out loud what you are doing with clutch pedal and gear lever as you actually do it. This will help uncover any bad clutch habits you may have developed. Improving them will result in your Porsche rewarding you with many trouble free miles of driving in its finest form.
4. Change the gearoil in your transmission every 30,000 miles. Use a good quality oil, such as Swepco 201, and inspect and clean the magnetic drain plug. If you find any large items on the drain plug, save them for later inspection by an experienced technician. Its also a good idea to remove the fill plug first, before you remove the drain plug. If the fill plug is frozen, which is not uncommon on 924s and 944s, you will have to remove it before you are able to refill the trans. Take a good look at the trans to see if there are any signs of leakage, particularly at the shift rod seal, the axle flange seals, or under the bellhousing.
5. If your clutch seems very hard to push in, replace the clutch cable. While it is true that the diaphragm springs in clutch pressure plates can work-harden and result in abnormally high clutch pedal effort, a worn clutch cable is equally likely to be the cause of this problem and far less costly to replace. Replacing a clutch assembly is an excellent time to replace the clutch cable, since even if not worn or frayed, replacing it at your convenience is better than having to replace it after it fails on the way to the Parade. Some clutches, however, have been replaced only to find that the pedal was still very hard to push in, in which case it may have been preferable to replace the clutch cable, clutch horseshoe spring, or clutch fork needle bearings rather than the entire clutch, any of which can cause the identical symptom. On the later model 911s with cable-operated clutches, there are auxiliary springs at both the clutch fork and pedal cluster assembly which must be inspected as well.
When replacing a clutch, its best to know what you're doing. I know of no commercially available repair manuals which properly address all of the items needing attention when replacing a Porsche clutch. 914s in particular are sensitive to the use of a reconditioned flywheel, and improper installation procedures can result in dramatically shortened clutch life or, in some cases, a clutch that will not function even when new. Porsche does not recommend resurfacing on the 911 and 968 dual-mass flywheels, although conversions are available. In short, follow these tips and you may not have to replace the clutch, or at least not nearly as often.
by Paul Lighthill
A recent call inquired about severe clutch chatter in a Carrera 2 that had only 30,000 miles on the odometer. It has been my experience during forty years of dealing with things mechanical that the operator is the single most important factor in determining a machines longevity and reliability. Perhaps nowhere is this more apparent than in the clutches and transmissions of our favorite cars, where PIO, or pilot-induced-oscillation as airline types call it, can shorten the life of these components to less than half of their design life.
From the first car to bear the distinguished name of Porsche to the very latest, the engineers at Gm�nd, Stuttgart, and Weisach have been in a major battle with weight. One hundred pounds of weight removed from a car is roughly equal to adding six horsepower, and furthermore, removing weight can reduce, not add costs, as increasing horsepower usually does.
Consequently, while Porsche has so far studiously avoided adopting the Lotus school of design (which states that if something doesn't break occasionally then it must be too heavy), they have gone to great lengths to ensure that the weight of their cars and the component parts is no more than is necessary for the intended purpose. This, of course, explains why Porsche cars have always excelled in performance and efficiency. It also explains why driver technique can be such a decisive factor in the longevity of components such as the clutch and transmission, since there is little excess material to allow for abuse or neglect.
For example, one late-model 911 experienced clutch failure at less than thirty thousand miles. An identical 911, but with a different owner, saw the clutch reach one hundred thousand miles. I just replaced a clutch in a 924S that had gone over 150,000 miles. If you would prefer that your clutch (and transmission) last a little longer, there are certain techniques that, once made habit, will serve to greatly prolong the life of these major (and costly) parts of your Porsche.
1. Avoid slipping the clutch whenever you start out from rest or when you change gears up or down. Of course some slipping is necessary when starting out, but if you watch the tach you will see that its possible to make entirely satisfactory starts using less than 2000 RPM. Less RPM equals less slippage. A good exercise is to stop your car on level ground, engage first gear, and then move off without using any throttle at all. This will help you find and memorize the friction point, or place in the clutch pedal travel where the clutch begins to engage. Its important to memorize the friction point for your car because if you cannot locate it quickly you are likely to slip the clutch and cause excessive wear.
When you shift up, let the clutch out smartly and don't open the throttle fully until the clutch is completely engaged. Coming in with too much throttle before the clutch is engaged will also cause slipping. When downshifting, mastering the double-clutch technique so that engine speed is matched to the speed of the rear wheels for the gear you are downshifting to will also prolong clutch life significantly. Double-clutching technique is thoroughly covered both in high performance driving schools as well as in racing textbooks. Drivers who practice it religiously on the street find that it becomes second nature and helps them achieve greater smoothness on both road and track.
2. Whenever you are stopped for a traffic light, throw the gear lever into neutral and let the clutch pedal out. Even though you may miss a second or two by having to put the pedal down and engage first gear when the light turns green, you will save much wear on both the clutch disc and release bearing. If you are uncomfortable about that semi waiting behind you, just watch the opposing light and go into first gear when you see it change to yellow. Any time you touch the clutch pedal, the internal parts of the clutch are wearing against each other, even if the pedal is all the way down. You would not want to rest your foot on the clutch pedal while driving, even lightly, for the same reason. The only condition under which the clutch will not wear is when the pedal is completely out and untouched. The same holds true for the shift lever; even the slight pressure of a resting hand is enough to cause wear on the shift forks inside the transmission, especially when multiplied over thousands of miles of driving.
3. Keep the clutch in proper adjustment(it should be checked at each routine service; see your owners manual for details). In some cases, particularly the last of the cable operated 911s (1975-86), correct adjustment is a rather involved procedure which requires adherence to the factory workshop manual and the correct setting of three adjustments. Even with the simpler 914s and earlier 911s there is a correct procedure and at least two adjustments that should be checked. Contrary to popular belief, the hydraulic clutches used by Porsche are also adjustable, and in one case that I am aware of with a 968, failure to check the adjustment led to damage that forced a transmission rebuild.
Once mastered, proper clutch technique is largely a matter of habit. You may wish to have a friend ride with you and observe your clutch habits. Or, simply try some commentary driving: describe out loud what you are doing with clutch pedal and gear lever as you actually do it. This will help uncover any bad clutch habits you may have developed. Improving them will result in your Porsche rewarding you with many trouble free miles of driving in its finest form.
4. Change the gearoil in your transmission every 30,000 miles. Use a good quality oil, such as Swepco 201, and inspect and clean the magnetic drain plug. If you find any large items on the drain plug, save them for later inspection by an experienced technician. Its also a good idea to remove the fill plug first, before you remove the drain plug. If the fill plug is frozen, which is not uncommon on 924s and 944s, you will have to remove it before you are able to refill the trans. Take a good look at the trans to see if there are any signs of leakage, particularly at the shift rod seal, the axle flange seals, or under the bellhousing.
5. If your clutch seems very hard to push in, replace the clutch cable. While it is true that the diaphragm springs in clutch pressure plates can work-harden and result in abnormally high clutch pedal effort, a worn clutch cable is equally likely to be the cause of this problem and far less costly to replace. Replacing a clutch assembly is an excellent time to replace the clutch cable, since even if not worn or frayed, replacing it at your convenience is better than having to replace it after it fails on the way to the Parade. Some clutches, however, have been replaced only to find that the pedal was still very hard to push in, in which case it may have been preferable to replace the clutch cable, clutch horseshoe spring, or clutch fork needle bearings rather than the entire clutch, any of which can cause the identical symptom. On the later model 911s with cable-operated clutches, there are auxiliary springs at both the clutch fork and pedal cluster assembly which must be inspected as well.
When replacing a clutch, its best to know what you're doing. I know of no commercially available repair manuals which properly address all of the items needing attention when replacing a Porsche clutch. 914s in particular are sensitive to the use of a reconditioned flywheel, and improper installation procedures can result in dramatically shortened clutch life or, in some cases, a clutch that will not function even when new. Porsche does not recommend resurfacing on the 911 and 968 dual-mass flywheels, although conversions are available. In short, follow these tips and you may not have to replace the clutch, or at least not nearly as often.
