Question about 2002 Volvo S80

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Would a failing vacuum booster effect the brake lights?...It seems when the pressure builds back up they work. When it drops they go on for a second then go out.... ALSO would a failing booster cause a rise and fall in rpm's during idle ?

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The booster uses vacumn to assist your foot pressure. A leaky seal or diaphragm in the booster or a bad hose from the engine to the booster will cause the pedal to drop as it loses power assist. I think the brake light switch is mounted under the dash by the brake pedal. Fix the booster now, it may save your life.

Posted on Feb 06, 2010

Testimonial: "Thanks ... I plan to fix the booster this week. Any thoughts on a new one vs. a remanufactured one?"

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Posted on Jan 02, 2017

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Why do i have loss of brake pressure


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Not sure if you have done all this.



BRAKE BOOSTER INSPECTION

Functional test:
1. With the engine stopped, Depress the brake pedal several times, then depress the pedal hard and hold that pressure for 15 seconds. If the pedal sinks, the master cylinder, brake line or a brake caliper is faulty
2. Start the engine with the pedal depressed. If the pedal sinks slightly, the vacuum booster is working. If the pedal height does not vary, the booster or the check valve is faulty

Leak Test:
1. Depress the brake pedal with the engine running then stop the engine. If the pedal height does not vary while depressed for 30 seconds, the vacuum booster is OK. If the pedal rises, the booster is faulty
2. With the engine stopped, depress the brake pedal several times using normal pressure. When the pedal is first depressed, it should be low. On consecutive applications, the pedal height should gradually rise. If the pedal position does not vary, check the booster check valve.

Check valve test:
1. Disconnect the brake booster vacuum hose at the booster.
2. Start the engine and let it idle. There should be a vacuum available. If no vacuum is available, the check valve is not working correctly. Replace the check valve and retest.

END TEST

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Brake pedal has alot of back pressure and car moves in gear.Have to press real hard to stop.How to check abs pump if has one where or brake booster or master cylinder?Don't know how to trouble shoot or...


The air seeping is a dead giveaway. Your power brakes are now manual brakes, but stiffer. The diaphram in the brake booster has torn and the hissing noise is the engine vacuum escaping (you hear it louder when you depress the pedal right?). Replace the booster and you will be fine. The brake lights probably don't work because you can't push the pedal down far enought to release the switch. Please rate. Thanks.

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