Volkswagen Golf / Golf GTI / Golf Variant. Manual - part 798

4.4

Vacuum System, Checking

⇒ “4.4.1 General Information”, page 123
⇒ “4.4.2  Brake Servo Tester VAS6721 , Connecting”,

page 123
⇒ “4.4.3 Vacuum, Checking”, page 124
⇒ “4.4.4 Leak Test”, page 125
⇒ “4.4.5 Vacuum, Creating with Hand Vacuum Pump VAS6213 ”,

page 126

4.4.1

General Information

Special tools and workshop equipment required
♦ Brake Servo Tester - VAS6721-
The following checks will be helpful when performing “Fault Find‐

ing” if there are complaints regarding the brake booster or the so-

called hard brake pedal.
The following components are included in the check:
♦ Brake Booster
♦ Seal between the master brake cylinder and the brake booster
♦ Check valve
♦ Vacuum hoses and connectors
♦ Vacuum pump (if equipped)
The geographic location will influence the measurement results.

The higher above sea level, the lower the air pressure.
Observe test requirements:
♦ Check all the vacuum hoses for damage (for example, tears

or damaged caused by animals) and make sure they are se‐

cure

♦ Maintain clean working conditions when working on the vac‐

uum system

♦ Clean the engine compartment before starting, if necessary

4.4.2

Brake Servo Tester - VAS6721- , Con‐

necting

– Remove the vacuum hose from the brake booster.
Pressing the brake pedal a few times beforehand makes it easier

to remove the vacuum hose.

– Connect the Brake Servo Tester - VAS6721-

-see following illustrations-.

Des‐

igna‐

tion

Com‐

po‐

nent

Explanation

A

Shut-

off

valve

In direction toward the vacuum hose, the check

valve and vacuum pump (if equipped)

B

Shut-

off

valve

♦ Opening the Brake Servo Tester - VAS6721-

makes it easier to remove.

♦ Open to simulate an incorrect source
♦ Connect the Hand Vacuum Pump - VAS6213- .

C Shut-

off

valve

Toward the brake booster

– Connect the Brake Servo Tester - VAS6721- hose -A- to the

vacuum hose.

– Push the adapter -C- into the brake booster.

4.4.3

Vacuum, Checking

Note

♦

The average earth atmospheric air pressure at sea level (N.

N.) is 1,013 mbar (15 psi).

♦

At higher altitudes the air pressure decreases dramatically

(approximately 11 mbar (.2 psi) per 1,000 m (3,281 ft) altitude).

♦

Local and time fluctuations will influence the vacuum.

♦

A cold engine, the Air Conditioning (A/C) switched being on

and even only the engine idling can negatively influence the

vacuum.

– Check all the vacuum hoses beforehand for damage (for ex‐

ample, tears or damaged caused by animals) and make sure

they are secure

– Connect the Brake Servo Tester - VAS6721- . Refer to

⇒ “4.4.2  Brake Servo Tester VAS6721 , Connecting”,

page 123

 .

– Open the shut-off valve -A-.

– Close the shut-off valves -B+C-.
– Start the warm (above 60 °C (140 °F)) engine and press the

accelerator pedal one time quickly (engine RPM higher than

2,000).

– Read the measured value displayed.
Normally (see note) the vacuum should be between 600 and 950

mbar (8.7 and 13.7 psi) (depending on the engine installed).
Check the vacuum system for leaks if the measured value is not

reached, even though all requirements (see notes).
– Create the vacuum using a Hand Vacuum Pump - VAS6213-

for comparison purposes. Refer to

⇒ “4.4.5 Vacuum, Creating with Hand Vacuum Pump

VAS6213 ”, page 126

 .

Opening the shut-off valve -B- makes it easier to remove the hose

connections and the adapter.

4.4.4

Leak Test

Note

♦

The average earth atmospheric air pressure at sea level (N.

N.) is 1,013 mbar (15 psi).

♦

At higher altitudes the air pressure decreases dramatically

(approximately 11 mbar (.2 psi) per 1,000 m (3,281 ft) altitude).

♦

Local and time fluctuations will influence the vacuum.

♦

A cold engine, the Air Conditioning (A/C) switched being on

and even only the engine idling can negatively influence the

vacuum.

– Check all the vacuum hoses beforehand for damage (for ex‐

ample, tears or damaged caused by animals) and make sure

they are secure

– Connect the Brake Servo Tester - VAS6721- . Refer to

⇒ “4.4.2  Brake Servo Tester VAS6721 , Connecting”,

page 123

 .

– Open the shut-off valve -A-.
– Close the shut-off valves -B+C-.
– Start the warm (greater than 60 °C (140 °F)) engine and press

the accelerator pedal one time quickly (engine RPM higher

than 2,000).

Normally (see note) the vacuum should be between 600 and 950

mbar (8.7 and 13.7 psi) (depending on the engine installed).

– Open the shut-off valve -C- and evacuate the brake booster.
– Turn off the engine.
– Read the measured value displayed and write it down.
The vacuum may drop 400 mbar (5.8 psi) within 12 hours.
If the vacuum drops more, check at the following points:
1 - Brake Booster
2 - Check valve, vacuum hoses and connections and vacuum

pump/intake manifold

The vacuum will drop considerably within a few seconds if there

are large leaks.

Checking the Vacuum Near the Brake Booster
– Close the shut-off valve -A- after creating the vacuum to test

the brake booster vacuum.

Note

Vacuum test near the check valve, vacuum hoses and connec‐

tions and vacuum pump/intake manifold.

– Close the shut-off valve -C- after creating the vacuum to check

the Brake Servo Tester - VAS6721- vacuum up to the intake

manifold or up to the vacuum pump.

Opening the shut-off valve -B- makes it easier to remove the hose

connections and the adapter.

4.4.5

Vacuum, Creating with Hand Vacuum

Pump - VAS6213-

In certain situations, the vacuum can be created using a Hand

Vacuum Pump - VAS6213- instead of using the engine or a vac‐

uum pump.
– Connect the Hand Vacuum Pump - VAS6213- to the vacuum

hose on the connection -B- on the Brake Servo Tester -

VAS6721- .

– Open the shut-off valve -B-.
– Create the vacuum using the Hand Vacuum Pump - VAS6213-

until a vacuum between 600 and 950 mbar (8.7 and 13.7 psi)

on the Brake Servo Tester - VAS6721- is displayed.

– Perform the tests.