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 upper part of the reservoir (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 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).
   WARNING: Risk of material damage if too much Pentosin is used or if Pentosin comes into contact with the coolant hoses when filling or topping up. Multiple steering operations (maneuvering) and/or actuating the clutch with the engine switched off affect the fluid level in the supply tank. The fluid level rises.

   • Coolant hoses may swell. Risk of fire if escaping Pentosin comes into contact with hot components and ignites.

   → To prevent any overfilling and thus any resulting overflow, the engine should be run for approx. 20 seconds immediately after checking the fluid level.

   → If coolant hoses come into contact with Pentosin, clean them thoroughly with water IMMEDIATELY. Replace visibly swollen coolant hoses.

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 plastic return line -arrow-  from the reservoir. To do this, push the red thrust ring in an axial direction, without tilting it, towards the tank and remove the line.
   Fig 1: Locating Return Line

   Courtesy of PORSCHE CARS NORTH AMERICA, INC.
3. Collect the fluid that runs out using suitable measuring equipment (suitable container) and read off the volume of fluid collected.
4. If more than 4 cm³ is collected after a measurement period of one hour, the pressure retaining valve in the clutch slave cylinder is faulty and the slave cylinder must be replaced. For information on removing and installing clutch slave cylinder, → 303019 REMOVING AND INSTALLING CLUTCH SLAVE CYLINDER .