How to test the vacuum source of brake system?

Vacuum brake booster is one important institute of auto brake system. By availing of vacuum negative pressure generated by working engine, it can amplify the drivers’ stepping force onto brake pedals, so as to produce greater braking force to stop the vehicles more quickly. Therefore when there is braking decline, stiff brake pedal or brake pedal without moving at all, the first to be suspected by the mechanics is the vacuum booster. Common problems to vacuum booster include booster diaphragm is damaged, or internal control valve fails which we have ever introduced in the previous post.?

In addition to the problems of brake booster itself, it is also notable to the problem of vacuum source that brake booster depends?on at working. When the negative pressure input into a brake booster is insufficient, consequently the braking force will be not enough either. Only eliminating the problems?of vacuum source, can?the?failure point be focused on the vacuum booster.??

Next, let’s take a look at how to check the vacuum source of brake booster.

Testing steps：

1) Find on the brake booster the vacuum hose connecting to the engine inlet manifold and the one-way valve, then disconnect the hose at the one-way valve.

2) Connect a vacuum gauge onto the engine vacuum hose.

3) Start the engine and keep idling until it reaches normal working temperature.

4) Check what the vacuum gauge reads at idling when the vehicle’s transmission is in in neutral or in parking gear, and the AC as well as other devices are turned off.?

5) It usually reads 45~70kPa on the vacuum gauge in normal situation.?

6) Once vacuum is not in this range, the first to be checked is whether the vacuum hose is aging, cracking, broken or clamp invalid or loose at connections, so as to make replacement or repairment accordingly.

7) After the vacuum hose is replaced, or the failure points are fixed, repeat the testing steps of (3) ~(5), and if vacuum is still not able to reach the standard range, there should be some problems?to the engine then. For instance, the air intake system is leaking, there is something wrong with the ventilation system of crankcase, or carbon tank solenoid valve goes failure, in this case, further investigation is needed, so that the failure points can be fixed accordingly.?

8) Even if the vacuum gauge shows the vacuum in the standard range, it is still necessary to furtherly check the one-way valve. Firstly, remove the one-way valve from the vacuum booster, to install onto the engine vacuum hose, and then connect the vacuum gauge to the one-way valve.?

9) Start the engine again, keep it idling, and turn off the engine after it reaches to the normal working temperature, then check whether the vacuum gauge reading keeps in the standard vacuum range.??

10) Once the vacuum gauge reading can not be kept, that means the one-way valve is in failure?and should be replaced.?

Warm Reminders from SY-PARTS

In regarding to the failure of insufficient braking force, mechanics should take the factor of vacuum booster into account, and know how to test the vacuum correctly and what standard it should be. In addition, it is notable that many vehicles are equipped with brake booster vacuum sensors, which enable diagnosis testers to read the data of the vacuum. But we need to take the possibilities of the?failures of?sensors or circuits into consideration, and connect a mechanical vacuum gauge to compare the testing result in necessity.

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