Drivetrain - Servicing the PSD Pressure Accumulator
Group3
Number
9603
Model
8 Cyl.
Part Identifier
3983
March 26, 1996
Subject:
Servicing the PSD Pressure Accumulator
ATTENTION:
Service Manager / Service Technician
Models Affected:
All 928's From Model Year 1990
Concern:
Correct removal and installation procedure of the pressure accumulator for the PSD system.
General Information:
The following information contains servicing instructions for removal and installation of the pressure accumulator in the PSD system. Due to high operating pressures found in the PSD system, servicing information for the PSD system should be followed precisely along with exercising the necessary safety precautions. Before removing the pressure accumulator of the PSD, you must release all of the hydraulic pressure in the system. See the 928 Porsche Workshop Manual Volume II Group 39, PSD Diagnosis/Troubleshooting.
Removing and Installing Pressure Accumulator
Removal:
1. With the ignition switch in the "0" position, pull off the plug connector on the pump motor (arrow in Figure 1).
2. Slowly remove all operating pressure from the PSD system through the bleeder screw on the magnetic locking valve assembly (# 9 in figure 2).
Caution:
The PSD system can have up to 180 bar of internal pressure. Use protective eye goggles and hand gloves when bleeding off pressure.
3. Unscrew the pressure accumulator (# 5 in figure 2) using a universal strap type oil filter wrench (Hazet # 2171-2 or equivalent). Under no circumstances should the pressure accumulator be loosened by turning the hex screw on top the accumulator housing. This will allow the gas pressure to escape and will necessitate replacement of the pressure accumulator.
Installing:
1. Install the pressure accumulator with a new 0-ring (# 4 in figure 2) lubricated only with brake fluid. Tighten the accumulator with a strap type oil filter wrench to 40 - 46 Nm (29 - 33 ft lbs).
IMPORTANT:
Use care not to over tighten the pressure accumulator as damage can occur around 70 Nm (50 ft lbs).
Under no circumstances should the hex screw on top the pressure accumulator be used to torque the pressure accumulator to the motor assembly.
Use only lint free shop towels during repairs. Absolute cleanliness is required.
2. Bleeding the accumulator and magnetic locking valve.
Proceed as follows:
Connect a bleeder bottle with a clear hose onto the bleeder screw of the magnetic locking valve and open the bleeder screw. With the ignition on (position 2), reconnect the electrical plug to the pump motor. As soon as the brake fluid leaving the bleeder screw is bubble free, disconnect the pump motor plug and close the bleeder screw.
Fill the accumulator completely. Do so by reconnecting the electrical plug to the pump motor. As soon as the pump motor turns off, disconnect the pump electrical plug. Slowly open the bleeder screw on the magnetic locking valve
Caution:
The PSD system can have up to 180 bar of internal pressure. Use goggles and gloves!
Note:
If the bleeding procedure is performed without a pressure bleeder, the fluid reservoir should be constantly checked and topped off as necessary.
3. The bleeding of the accumulator should be performed 2 times or until the escaping brake fluid is bubble free.
4. Bleeding of the Lock Cylinder and Pressure Line.
For this procedure, the magnetic locking valve is operated by the Porsche System Tester 9288. The high pressure in the magnetic valve pulses through the pressure line into the check valve and then into the lock cylinder. Attach a bleeder bottle with a clear hose to the bleeder screw of the lock cylinder and allow the brake fluid to escape until bubble free.
5. When the repair and bleeding procedures are completed, top up the fluid reservoir after the accumulator is fully charged.