Possible causes of deviations from prescribed value

Checking conditions not met. E.g. wheels not completely locked, manometer or locking hydraulics not properly bled.

Transverse lock values not correct, causing deviations for longitudinal lock

Longitudinal lock clutch plates not in good condition

Hydraulic pressure not acting on clutch plates at level indicated, e.g. due to incorrectly adjusted end support screw of engaging lever (only with adjustable version / engaging lever is in contact).

911 Carrera 4 All-wheel drive / Antiblock system



7. Remove manometer with System

- Cautiously open measuring line on longitudinal lock cyl

Tester switched off and ignition key

inder (due to admission pressure). Remove measuring

removed (so only admission pressure

line and fit bleed valve.

in measuring line applies). Fit bleed

- Bleed longitudinal lock using System Tester 9288.

valve and bleed longitudinal lock.

Switch off System Tester.

8. Fit rear brake calipers and discon

- Tighten brake cylinder fastening bolts to 85 Nm

nect System Tester. Correct brake

(62.3 ftlb). Fit bracket on rear axle links and fit brake

fluid level. Check locking hydraulics

hose bracket.

for leaks.

Operate brake pedal several times.

- Disconnect System Tester and correct brake fluid level

with pressure reservoir completely full (after pump unit

has automatically switched off).

On no account top up above "max. " mark.

- Check exterior of hydraulic lines (brake and lock) in area

of rear axle for leaks.

To activate full system pressure in lock servo cylinders,

turn full lock button on center console to the right with

ignition switched on. To disengage lock turn switch to


9. Fit rear underfloor panels, com

ponent protection elements and rear


Carry out short test drive (locks and

function of brakes).

Limit values - locking moment to pressure

Transverse lock

Hydraulic Turning Brake Porsche Rally

Longitudinal lock

Locking moment (Nm)

Admission Porsche 964

Checking admission valves in locking hydraulics (lock activation) General

The admission valves are usually also checked when the friction values of the longitudinal and transverse locks are checked (point 4).

One admission valve is located in the pressure lines in front of each of the longitudinal and transverse lock servo cylinders (arrow).

If admission pressure is too high, creaking noises can occur. No pressure is also not good, for reasons of wear and handling dynamics. When replacement is necessary, do not confuse with PSD admission valve in the 928.

911 Carera Pcv Valve
Prescribed values / differentiating characteristics of admission valves


Prese, value


911 Carrera 4

approx. 2.0...3.5 bar

2 - 3 stamped on valve

928 with PSD

approx. 3.0...4.5 bar

3 - 4 stamped on valve

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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