Question about 1990 Porsche 928

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My 930 1976 have too little vacuum to the brake booster. The car can brake, but the pedal require a lot of pressure. The car run fine. When I block / unblock the vacuum hose with a finger I can hear a difference in engine speed. The hose is undemaged from booster to intake manifold. The return valve at booster is ok.

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The vacuum may not seem strong enough,but most likely is,the check valve at the booster assures that the vacuum is stored in the booster,so it has enough vacuum to operate correctly.The problem will be the booster,or,the brakes themselves are not stopping the car.Remember,the vehicle has abs also,and the abs will not allow the car to stop to sudden in the first place,but I would have the brake liners,and rotors checked out first,before replacing the booster.Now,if the brake pedal is just plain hard,then it is likely the booster.I hope this was helpful,if so,please let us know,thank you.

Posted on Jan 30, 2010

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Posted on Jan 02, 2017

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2 Answers

Why do i have loss of brake pressure


Long shot: Bad master cylinder - Typically the brake pedal will slowly sink to the floor. On early 2000 vintage Chrysler products you need to check brake lines as they have been known to rust (and fail catastrophically)

Jul 04, 2014 | 2003 Jeep Wrangler

2 Answers

How do you know that a brake booster is bad?


Booster problems are rare but they do go bad sometimes.
A bad booster generally causes the brake pedal to feel hard to push down, and a lot of pressure on the brake pedal is required to make the car stop.
Rarely, a vacuum brake booster will develop a vacuum leak, which can cause engine performance problems, hissing or whistling noise, as well as requiring increased pressure on the brake pedal to stop.

The first test:
With the vehicle parked, turned OFF, and the parking brake set, pump the brake pedal 5 to 6 times. If the pedal gets harder to push after several times, your booster is probably good.

The second test (To make sure):
After the test above, without making any changes, press and hold the brake pedal with light to moderate pressure.
Now with your foot still on the brake pedal, start the vehicle.
If the booster is good, you will feel the pedal go down when the engine starts.

Hope this helps!

Jun 21, 2014 | 1993 Cadillac DeVille

1 Answer

Why is it so hard to apply brake pedal?


_______power brake booster, check vacuum to booster and the check valve for brake booster. primary symtom is high hard pedal that requires greater then normal pedal pressure to stop car. testing booster= pump brakes several times with engine off to deplete stored vacuum. turn on engine with pushing slightly on brake pedal. you should be able to feel the pedal fade away a bit, and then become firm. But not hard. if you feel nothing at the pedal when engine starts. Brake booster is not working. Good-day! make sure vacuum is going to booster with engine running. it may just be a bad vacuum line or check valve.

Apr 30, 2014 | 1984 Buick Skyhawk

1 Answer

Polo 1.4 - Im used to driving an automatic, but the Polo is manual. When I stall th engine, the foot brakes won't work. This is scary, especially on a hill!


Most likely the car has Power-Assisted brakes, Almost all vehicles today do. They allow us to stop the car with very little pressure required on the brake pedal, as the system uses engine vacuum to do the work of our leg. When you stall the car, you lose engine vacuum. This means that the brake pedal will still work, but requires far more effort to push since there is no vacuum assist. Most vehicles have a check valve at the input to the power brake booster to hold vacuum on the booster when the vehicle shuts down. This provides you with one last free press of the pedal. If you are not getting that, either your car does not have a check valve, or the valve is faulty.

Nov 14, 2013 | Cars & Trucks

1 Answer

Vw golf 2000 the brake pedal is to soft when you apply it and seems like is not going to stop but it does, what is the problem?


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

Nov 06, 2012 | Volkswagen Cars & Trucks

1 Answer

1937 ford coupe relpaced booster brake pressure when off/no pressure when started


Try checking with either propane or water mist on all hoses and surfaces where generated vacuum could escape.

Activator rod from Brake pedal to Master cylinder can be adjustable on some models.

Jul 20, 2017 | Ford C Cars & Trucks

1 Answer

I replaced the master cylinder and brake pads and my brakes still dont work on my 1998 chrysler sebring


Have you tested your brake booster and your calipers?Your brake booster doesn't make any noise, and it doesn't use any electricity or gasoline, but it ensures that you can stop your car with only a light touch of the brake pedal. Things weren't always like that: before the invention of the vacuum brake booster, cars still stopped. It's just that you had to really stomp on the brake pedal. The modern brake booster is an ingenious device that operates using something that your engine generates whenever it's running: vacuum. The brake booster takes engine vacuum via a rubber hose that runs from the intake manifold, and the brake booster uses that vacuum to amplify the pressure you put on the pedal. A light application of the brakes is translated by the brake booster into significantly more pressure on the brake master cylinder, ensuring that your car stops quickly. So what happens to the brake booster if your car stalls, resulting in a loss of engine vacuum? Early designers realized that gas engines were hardly foolproof, so they designed a little check valve into the brake booster circuit. The brake booster stores enough vacuum to provide full boost for two or three pedal applications even after the engine dies. The check valve on the brake booster is what keeps that vacuum from leaking out. And speaking of leaks, that's the reason most brake booster units have to be replaced. As your brake booster ages, the rubber seals and diaphragms that hold the vacuum tend to wear out and crack. If the brake booster can't hold vacuum (despite the check valve's best efforts), its time is up and you'll need a new or remanufactured new brake booster.

Jun 14, 2011 | 1999 Chrysler Sebring

2 Answers

I have very little rear brakes on my 91 w350. the shoes are fine and so are the wheel cylinders. I have recently replaced the master cylinder and had the system power bled at a shop. Is it the...


I assume you bled the rest of the system. If so check your rear adjustment. Adjust the parking brake at the same time. If no fix, then open up your rear brakes and inspect the hardware, cylinder/caliper, and adjuster. Only after all that would I suspect the proportioning valve. Ways to test that vary vehicle to vehicle. Good luck!

Apr 20, 2010 | Dodge W250 Cars & Trucks

1 Answer

Stalls or wants to turn off when pushing brakes


Check for vacuum leak within power brake servo unit.
Remove vacuum hose from brake servo and block off the open vacuum line from the engine. Check that engine then runs normally when brakes applied.
Do not drive the vehicle with the vacuum servo disconnected, as the brakes may not be effective. - The pedal pressure required to apply the brakes effectively may exceed your capabilities.

If the brake booster servo diaphragm is leaking it will need to be replaced/repaired.

Nov 03, 2009 | 1991 Honda Accord

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