How does the Brake Booster Solenoid work?

[sapote]

I will admit that it may be my braking technique causing these issues. I do left foot brake. So its possible there may be some crossover between fully off throttle and brake application..

Now you’re more conscious about releasing gas pedal before braking and this should build up boost vac.

im left foot braking in 2-pedal cars and right foot braking in 3-pedal too

[eacmen]

IIRC...when the car is off, the solenoid is open. Once you turn the car on, the solenoid energizes and closes which isolates the booster from the engine vacuum - the engine pulls air through the intake, solenoid, booster, two way valve, and the air rail behind the throttle body butterflies. When you step on the brake, it opens the hall effect switch, ECU sees the open circuit and degenergizes the solenoid which provides power assist.

Unplug the solenoid, drive the car until the brakes lock on (won't take long) and then with the car running pull the vac hose off the booster, there will be vacuum. Do the same thing with the solenoid plugged in and car running, there will be no vacuum. As soon as you step on the brake, you'll have vacuum on that line.

The system is designed to have power assist if something fails.

There is no sucking jet pump in this...its a form of a check valve. I discovered this when mine fell apart. But I would check it to make sure its not falling apart. Mine came apart at the seam.

If the valve is good, the pedal is hard and the brakes are working - it's a booster, master cylinder, ABS pump, or caliper issue.

I made this diagram that hopefully clears up how this system works. The Solenoid just controls if there is airflow to power the venturi/sucking jet pump. Normally the booster is harvesting engine vacuum and storing it by way of the check valve and check valve seal.

[heinzboehmer]

I made this diagram that hopefully clears up how this system works. The Solenoid just controls if there is airflow to power the venturi/sucking jet pump. Normally the booster is harvesting engine vacuum and storing it by way of the check valve and check valve seal.

Unsolicited nit: I would swap the direction of the red arrows so that they're consistent with the direction of fluid flow.

[eacmen]

Unsolicited nit: I would swap the direction of the red arrows so that they're consistent with the direction of fluid flow.

not gonna lie. i did waffle back and forth as to how to draw those red arrows.