Pressure Regulator

From Citroen SM Wiki

See also Brake Pad Wear.

Related Modification

A good mod on the SM is to re-route the overflow return pipe from the regulator.

Remove the regulator and remove the cover integral with the overflow/return pipe stub. Refit it 180 degrees i.e. about face. This allows you to (just) fit the rubber pipe on it without removing the pump etc etc. Care, the spring under it is strong.

Compensating for old spring

While doing this you can place another 1mm shim above the spring in the cover with the others you will find there to lift up the pressure again. DO NOT fit more without a proper test gauge.

When is it bad?

Regular 'clicking' from the regulator (say less than every 10 seconds stationary and engine at idle) means a possible U/S accumulator sphere, not the regulator at fault. A simple fail test (NOT a pass test) is look in the hole, and if you cannot see the bottom of the diaphragm it is scrap. If your Accumulator sphere dribbles oil when removed it's beyond repair or safe use. Throw it away.

Testing Regulator

To check pressure, you have to make up an adapter from an old bit of Citroen hydraulic pipe with Citroen fittings on one end and an adapter to an appropriate pressure gauge - say up to 250bar/3500psi on the other end. A bar is nearly 1kg/cm2.

  1. Release the pressure by turning the 12mm nut a turn or so.
  2. Remove the output pipe from the regulator and fit the gauge.
  3. Start the engine and let it idle.
  4. Slowly close the 12mm nut. The system will pressurise to the cut-out pressure. Make a note of it.
  5. Loosen the 12mm nut slightly so as to see the pressure fall slowly. Note the pressure the pump cuts in again at. This is the cut-in pressure.
  6. Cycle it if you want to verify.


  • cut-in: 140-150 kg/cm2, (1990-2140 psi)
  • cut-out: 160-175 kg/cm2, (2350-2490 psi)
    • 0.7mm increase in shim is +7kg/100psi