Volkswagen Workshop Service and Repair Manuals > Golf Mk6 > Brake systems | Brakes, hydraulics, regulator, servo | Brake servo/brake master cylinder (right-hand drive vehicle) | Checking brake servo vacuum system

Checking for leaks

Note

t	The average air pressure of the earth's atmosphere at sea level is 1013 mbar and decreases steeply as the altitude increases (approx. 100 mbar/1,000 m altitude). Local and time fluctuations also influence vacuum generation.

t	A cold engine, a switched-on air-conditioning system as well as engine idling have an adverse influence on generation of a vacuum.

–	Before starting work, check all vacuum hoses for damage (e.g. cracks or marten bite) and to check that they are correctly and firmly attached

–	Connect brake servo vacuum gauge -VAS 6721- → Chapter.

–	Open cut-off valve -A-.

–	Close cut-off valves -B+C-.

–	Start warm engine (>60° C), press accelerator briefly (engine speed greater than 2000/min).

Normally (see notes), the vacuum that is generated should be between 600 and 950 mbar (depending on engine size).

–	Open cut-off valve -C- to evacuate brake servo.

–	Switch off engine.

–	Read and make a note of measured value shown.

A vacuum decrease of 400 mbar in 12 hours is permissible.

If the vacuum decrease is greater, check for leaks in the vicinity of...

1 -	Brake servo

2 -	non-return valve, vacuum hoses with connectors or vacuum pump/intake pipe

If there are large leaks, the vacuum decreases steeply within a few seconds.

Vacuum check in vicinity of brake servo:

–	After generation of vacuum, close cut-off valve -A- in order to check brake servo vacuum system.

Vacuum check in vicinity of non-return valve, vacuum hoses with connectors and vacuum pump/intake pipe:

–	After generation of a vacuum, close cut-off valve -C- in order to check vacuum system from brake servo vacuum gauge -VAS 6721- to intake pipe or to vacuum pump.

Open cut-off valve -B- to facilitate removal of hose connections and adapter.

Volkswagen Workshop Service and Repair Manuals