Maintaining a brake vacuum pump (brake booster)

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  • OVERALL DIFFICULTY INDEX: 3/10
  • IF YOU HAVE NO TOOLS YOU SPEND $30 TO GET THEM FOR THIS JOB
  • IF YOU HAVE NO EXPERIENCE YOU SPEND 3 HOURS TO CARRY OUT THIS JOB
  • RISK OF BURNS, SEE BELOW
BEFORE YOU START
  • Always work on a cold engine to avoid burns.
  • The below works are valid for attempting a repair against a loss of servo assistance when moving a vehicle slowly and shifting to neutral in particular. Do not consider this intervention for a permanent loss of the brake servo assistance or if the brake pedal becomes stiff when driving!
  • The vacuum pump in this case is mounted on the cylinder head and driven by the camshaft. Those works have been carried out on a Peugeot 5008 1.6 THP 156 BS (EP6 engine) but remain similar on all EP6 1.6 VTi or THP engines like the ones of the Mini Cooper and on other engines equipped with camshaft mounted vacuum pumps.
DISCLAIMER:
Our pictorials are of informative nature and do illustrate works carried out by ourselves at our own premises for our own use and satisfaction.
Readers who envisage to carry out similar works inspired by the below method shall do this at their own risks and liability.

Symptoms of a failing brake and turbo vacuum pump

The vacuum pump generates vacuum when the engine is started and while it remains on, in order to provide brake boost on one hand, and vacuum for turbo controls on the other hand, in case the engine is equipped with a turbo.
How does the vacuum pump work when braking?
It generates the vacuum needed by the brake booster, also called vacuum servo.
Symptoms of a failing vacuum pump include:
  • Brake pedal gets stiff at low speed when shifting to neutral on a red light or in a traffic jam, or else is normal
  • Brake pedal gets stiff upon starting the vehicle and moving it the first time like for example getting out of a parking space, then becomes normal
  • Brake pedal gets stiff and hard to press all the time
In the first two cases, you need to intervene quickly and try cleaning and maintaining your vacuum pump, or replacing it.
In the second case, you should not drive your vehicle indeed, rather diagnose your braking system in order to determine of the cause is the vacuum pump or the vacuum servo, then replace the defective part.
Vacuum pump partial failure, rarely leads to a turbo failure, which is more impacted by the turbo valves failures and the vacuum tubes enlargement with time. Check our below links for further readings and further understanding how a turbo is controlled by vacuum.

Brake vacuum pump removal

Remove whatever air hoses hiding the pump.
Disconnect the servo brake vacuum hose from the pump.
Unscrew the pump holding bolts (left and middle) and take it out. You might need to use a large slotted screwdriver as a lever (right).
The pump is driven by the exhaust camshaft (left).
Remove the turbocharging regulation vacuum hose in case you did not do so before (right).

Brake vacuum pump dismantling and cleaning

Put the vacuum pump in a clean tray and remove the cover screws (left).
Remove the vacuum outlets (middle).
The pump is simple in construction and made of robust material and components. Its weak point however is explained further below.
​Note well how it is lubricated by the engine oil itself which with time becomes thick and sticky (right).
Now here comes the problem of the vacuum pump: both vacuum connections to the servo and turbo regulation circuit contain a basic check valve made of a rubber disc and a spring. The disc can stick in place or the opening can get obstructed by the thickened and aged oil.
The fix consists of freeing the check valves by cleaning them, eventually replacing them.
NOTE: the vacuum pump connector is available as a spare part from our partners' store, in case you'd like to replace it:
  • Put the connectors of the vacuum pump in a glass jar filled with a little new motor oil and spray them well with a carb cleaner (left).
  • Leave them for not less than 30 minutes soaking into the mix of carb cleaner and oil. Do not immerse them in the carb cleaner alone.
  • Use compressed air to dry them up (middle).
  • You should be able to see now the color of each component of the vacuum pump connectors.
  • Gently blow through them with your mouth in the same vacuum direction (outside to inside) and make sure air passes through.
Clean well all other parts of your vacuum pump to get the rid of the aged oil:

Refitting

  • Replace the vacuum pump connectors' seals with new ones. 
  • Use exclusively high temperature EPDM or Silicone O-ring seals for the connectors.
  • Replace the pump to cylinder head seal, available as a spare.
  • Pour some 50 ml of engine oil into the pump and one drop into each connector prior to closing the cover.
  • Use RTV silicone gasket maker applied directly on the vacuum pump cover seal if you don't find a match for this one.
  • This is the only place where the RTV gasket maker can be used.
Now clean well the servo vacuum hose connector with your carb cleaner and use some grease on the pump and servo connectors prior to reinstalling it.
Test the vehicle over a period of days.
Replace the vacuum pump with a new one if this fix doesn't eliminate the above described symptom.
Note: testing the pump with a vacuum gauge won't necessarily return a clear result since such symptom is of intermittent and unexpected nature. Click on the below link to see how to test the pump with a vacuum gauge and replace it:
You may buy your Peugeot / Citroën / Mini / Opel brake vacuum pump from our partners' stores, make sure of the compatibility with your vehicle:

See also our complete EP6 engine repair manual:

And more DIY tips for all types of cars: