Porsche Clutch Systems 101Posted on: 29, March, 2012
Manual gearboxes have always been synonymous with Porsche. Although the Sportomatic, Tiptronic and currently the PDK automatic transmissions are great and have a loyal following, there is just something really cool about working the clutch and shifting through the gears in a Porsche. Every car with a manual gearbox includes a clutch at no additional cost, well at least initially.
We are often asked how one knows when a clutch is worn out or going bad. Generally, this can be dependant on a number of factors and in some cases when the vehicle was manufactured. For example, all Porsche’s that have a clutch cable, if there is no more adjustment length on the cable available, and the clutch is slipping; it is time for a clutch replacement. Porsche has not utilized a clutch cable since model year (MY) 1986, so that method of diagnosis is only applicable to that year and earlier models.
Starting in MY 1987, Porsche utilized a hydraulically actuated clutch system. Like many other manufacturers, most all Porsche hydraulic clutches operate using (DOT 4) brake system fluid and share a fluid reservoir with the brake system. Beginning in 1996, the 993 Turbo model utilized a specific hydraulic fluid, Pentosin CHF202, and a dedicated clutch fluid reservoir located in the front trunk. These models share this fluid for the operation of the clutch and power steering systems.
On a hydraulic type clutch system, the only way to know if a clutch is worn out is to combine the information at hand, or foot for that matter. These include:
- The age and or mileage on the clutch. 50K to 70K miles on average for a normally aspirated (NA) model is generally normal; 35K miles on Turbocharged models is not that unusual.
- The feel of the clutch pedal, is the clutch pedal stiff to depress? If the clutch is stiff to operate then the clutch may be due. Some models utilize a hydra-accumulator or “power spring” (as Porsche calls it), these assist the driver to both depress and return the clutch pedal. Note; if the cruise control system is not operating then check the clutch pedal power spring, it might be the culprit.
- The release point of the clutch. When the car is at a full stop, move the shifter into first gear and as you release the clutch pedal notice at what point in the pedal travel (up from the floorboard) the car begins to move. The lower the release point the better.
- The final and most obvious indicator is a slipping clutch. When analyzing the condition of the clutch remember that it is not just the clutch disc that can go bad. A worn out and noisy release bearing (throw out bearing) or pilot bearing can be the problem. Also, a leaking engine rear main (flywheel) or a gearbox main-shaft seal can allow oil to get onto the clutch disc and cause it to slip or chatter. Chatter is when the car begins to shutter (sometimes violently) as the clutch is released.
On the 993 and 996 Turbocharged models (except for the GT2), when the clutch fluid reservoir has a symptom of overflowing fluid (rising fluid level) and the power steering reservoir is losing fluid, at the same time, the clutch slave cylinder is bypassing fluid internally and is faulty thus requiring replacement. These same models utilize a Hydra-accumulator (as mentioned above) to assist the operator in depressing the clutch. It is not an uncommon scenario for the hydra-accumulator to fail and need replacement at some point in the car’s life.
One way to help extend the life of your clutch is to become very proficient at operating it, taking very little time to let it out during take offs. Staying off hills is also a critical clutch savior. When stopped for any period of time, take the car out of gear and let your foot off of the clutch pedal, this will help extend the life of the throw out bearing.
Tony Callas & Tom Prine