3. Checking Pressure Retaining Valve In Clutch Slave Cylinder

Information 

• Checking the pressure retaining valve in the clutch slave cylinder (Test 3) is a direct measurement, whereas the pressure retaining valve in the pressure control valve (Test 4) cannot be checked directly. 
• If there is no clutch boost after an idle period of 24 hours, at least one of the two pressure retaining valves or the pressure control valve is definitely defective. There may be no clutch boost after an extended idle period (even after one day at high temperatures) during initial actuation, depending on the system. Full clutch boost and functional capability is available immediately when you start the engine. 
• Prior to the following check, perform a visual inspection (externally!) to ensure that the system is not leaking! 

1. Warm engine up to operating temperature (approx. 80°C).
2. With the engine switched off and the pressure accumulator filled (before switching off the engine, the engine must have been run for approx. 20 seconds without pressing the clutch pedal), remove the return line -2-  at the clutch slave cylinder.

   To do this, press evenly on the red ring -2a-  (without tilting it/never on one side) and pull the line -2-  out while pressing (releasing) it.

   Use disassembly tool Nr.21  to release the line.

   Fig 1: Identifying Lines At Clutch Slave Cylinder

   Courtesy of PORSCHE CARS NORTH AMERICA, INC.
3. Collect the fluid emerging from the clutch slave cylinder in a suitable measuring device (suitable vessel) and measure the volume.

   To make it easier to catch the emerging fluid (restricted space in the area), a new modified return line -2-  can be used as an aid. Fit (attach) this return line on the clutch slave cylinder.

4. If more than 4 cm³ of fluid is collected within a measurement period of one hour, the pressure retaining valve in the clutch slave cylinder is defective and the slave cylinder must be replaced.

   → 303019 REMOVING AND INSTALLING CLUTCH SLAVE CYLINDER .