Hissing Sound when Brakes are applied
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Honda-Tech Member
Joined: Sep 2014
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Hissing Sound when Brakes are applied
So I have a 93 Del Sol and every time I step on the breaks theres this hissing sound coming from the brake pedal and also sometimes when I step on the gas. Also when the brake is applied my RPM like to jump from 1000 rpm when on a full stop to 1500-2000 rpm when brake is applied. Any ideas please car has been giving me nothing but issues since I purchased it.
Re: Hissing Sound when Brakes are applied
Or a damaged vacuum line, or a brake fluid leak. Is there any brake fade when you're stopping? In other words, do you have to push your foot down harder to maintain the same pressure feel on the pedal?
Also, basic brake system tests, stolen from IWM:
Also, basic brake system tests, stolen from IWM:
Functional Test
1. With the engine off, press the brake pedal several times to deplete the vacuum reservoir, then firmly press-and-hold the brake pedal for 15 seconds. If the brake pedal sinks, either the MC is internally bypassing, or there is a leak in the brake system. (mc, lines, prop valve, calipers, wheel cylinders, etc)
2. With the brake pedal pressed, start the engine. If the pedal sinks slightly, the vacuum booster is okay. However, if the brake pedal height does not vary, the check valve or booster is faulty.
3. With the engine running, lightly press the brake pedal. If the pedal sinks more than 3/8" (10mm) in three minutes, the master cylinder is faulty. (If the A/C is on, a slight change in the height of the brake pedal is normal.)
Leak Test
1. With the engine running, press-and-hold the brake pedal, then turn the engine off. If the pedal height does not vary while pressed for 30 seconds, the vacuum booster is okay. If the brake pedal rises, the booster is bad.
2. Turn the engine off and wait for about 30 seconds. Press the brake pedal several times using normal pressure. When the brake pedal is first pressed, it should be low, then gradually rise with each consecutive compression. If the position of the pedal does not vary, inspect the booster check valve.
3. Disconnect the vacuum hose (check valve built-in) at the brake booster.
4. Start the engine and let it idle. There should be vacuum available. If there is no vacuum, the check valve is not functioning properly. Replace the vacuum hose, and retest.
5. With the engine running, pinch the vacuum hose between the check valve and the booster.
6. Turn the engine off and wait for about 30 seconds. Press the brake pedal several times using normal pressure. Again, the brake pedal should be low when it's first pressed, gradually rising with each consecutive compression. If the pedal position does not vary, replace the booster. If the pedal position does vary, replace the vacuum hose / check valve assembly.
1. With the engine off, press the brake pedal several times to deplete the vacuum reservoir, then firmly press-and-hold the brake pedal for 15 seconds. If the brake pedal sinks, either the MC is internally bypassing, or there is a leak in the brake system. (mc, lines, prop valve, calipers, wheel cylinders, etc)
2. With the brake pedal pressed, start the engine. If the pedal sinks slightly, the vacuum booster is okay. However, if the brake pedal height does not vary, the check valve or booster is faulty.
3. With the engine running, lightly press the brake pedal. If the pedal sinks more than 3/8" (10mm) in three minutes, the master cylinder is faulty. (If the A/C is on, a slight change in the height of the brake pedal is normal.)
Leak Test
1. With the engine running, press-and-hold the brake pedal, then turn the engine off. If the pedal height does not vary while pressed for 30 seconds, the vacuum booster is okay. If the brake pedal rises, the booster is bad.
2. Turn the engine off and wait for about 30 seconds. Press the brake pedal several times using normal pressure. When the brake pedal is first pressed, it should be low, then gradually rise with each consecutive compression. If the position of the pedal does not vary, inspect the booster check valve.
3. Disconnect the vacuum hose (check valve built-in) at the brake booster.
4. Start the engine and let it idle. There should be vacuum available. If there is no vacuum, the check valve is not functioning properly. Replace the vacuum hose, and retest.
5. With the engine running, pinch the vacuum hose between the check valve and the booster.
6. Turn the engine off and wait for about 30 seconds. Press the brake pedal several times using normal pressure. Again, the brake pedal should be low when it's first pressed, gradually rising with each consecutive compression. If the pedal position does not vary, replace the booster. If the pedal position does vary, replace the vacuum hose / check valve assembly.
Thread Starter
Honda-Tech Member
Joined: Sep 2014
Posts: 17
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Re: Hissing Sound when Brakes are applied
I just saw this just now and ill try this tomorrow morning thanks for the info though. And to answer your question theres times when I'm braking the pedal just sink all of a sudden and times where I have to push down extra hard just to brake and maintain the pressure.
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