When the engine is off or if the vacuum hose has a leak, the one-way check valve ensures no external air enters the vacuum brake booster. The power brake booster has to provide the driver enough boost to perform several stops if the engine stops running remember, no running engine means no engine vacuum via the intake manifold.
When the brake pedal is released, all that built-up amplifying pressure in the vacuum brake booster has to go somewhere. The brake booster check valve helps release that pressure, drawing out all the unnecessary air through the vacuum hose.
There would be continuous pressure on your braking parts, which could break down from the pressure buildup. Because the check valve sucks out air, it keeps air from entering the brake lines through the master cylinder.
An air bubble in any brake line could have a severe effect on the performance of the braking system. The symptoms of a bad brake booster check valve are similar to the symptoms of a failed vacuum booster system. If the check valve is broken — possibly from a cracked grommet that usually keeps it sealed — the valve will likely create a vacuum leak.
Reduced vacuum in the booster means less amplifying power. Changes in how your brake pedal feels are usually due to potential issues in the power brakes, and you need to get your vehicle to a mechanic as soon as you can. As the bad check valve gradually loses effectiveness, the air that it should regulate can end up in the brake master cylinder, enter the brake fluid, and progress as air bubbles in the brake line. Any air bubble in the brake fluid is going to reduce the hydraulic pressure that flows back and forth between the master cylinder and brake caliper at each wheel.
Your brake pedal might even sink to the vehicle floor. A vacuum leak from the brake booster can cause unregulated air in your induction system and create a lean fuel mix in the engine. While this is typically caused by a leaking vacuum brake booster diaphragm, a broken check valve could also be the culprit behind a vacuum leak. In this situation, call a mechanic to come to you or have your car towed to a garage.
In this case, your mechanic will likely have to replace both the hose and check valve. However, you should be aware that repairs might involve more than a check valve fix. If your brake booster check valve has been faulty for a while, other brake system parts could have been affected — like possible air bubbles in the brake lines that need to be bled out. To keep things simple, look no further than mobile mechanic RepairSmith.
RepairSmith is a convenient mobile vehicle repair and maintenance solutio n that checks all those boxes and more. More than likely the vacuum line will have to be purchased from the dealership to get the correct one. Q: I do not know where my brake booster vacuum line connects to my engine. My car has miles.
My car has a manual transmission. Robert Kulp Automotive Mechanic. Good luck! Jamahl Walker Automotive Mechanic. The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details. Home Questions. Experienced Mechanic? Apply Now. What others are asking Coolant light is on The coolant temperature sensor may have a malfunction or your engine computer needs to be reprogrammed.
The problem may occur when going through temperature extremes. The computer can sometimes read a rapid change of temperature which will turn on the Read more. Power steering gets stuck and heavy but hasn't stopped working Normally, it's the rack and pinion. A lot of times, that You can see if the valves have carbon build-up and if they need cleaning. However, if there is no change in the pedal position or feel, the booster is not working.
Check the power steering system to determine whether the problem is in the pump or the booster. Similar to the vacuum booster, the hydro-boost is equipped with a backup or reserve in case the source of pressurized fluid is lost. In the event of a loss of pressurized fluid, the accumulator will provide two to three power-assisted stops.
Once you have depleted all of the stored pressure, the brakes will no longer have power assist and will be manual in their operation. Hydro-Boost Accumulator Test: To test the ability of the system to store a short-term high-pressure charge in the accumulator, start the engine and allow it to idle.
Charge the accumulator by turning the steering wheel slowly one time from lock to lock. Do not hold the steering at full lock for more than five seconds. Switch the engine off, release the steering wheel, and repeatedly apply the brake pedal with medium force. If the accumulator can hold a charge, a Hydro-Boost I unit will provide two or three power-assisted applications, while a Hydro-Boost II unit will only provide one or two.
To test the ability of the system to store a long-term charge, start the engine and recharge the accumulator as described previously. As the accumulator charges on a Hydro-Boost I system, a slight hissing sound should be heard as fluid rushes through the accumulator-charging orifice. Once the accumulator is charged, switch the engine off and do not apply the pedal for one hour. At the end of the hour, repeatedly apply the brake pedal with medium force.
In either case, the booster must be rebuilt or replaced. However, if a Hydro-Boost I system fails the test but does not make the hissing sound to indicate the accumulator is charging, the fluid in the system is probably contaminated. Simply flushing the hydro-boost system may cure the problem. Never begin any work on a hydro-boost system until you have discharged the dangerously high pressure stored in the accumulator by pumping the brake pedal numerous times with the engine off.
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