# disc brake dilema



## iamrfixit (Jan 30, 2011)

Is the brake light on the dash on? 
That would mean half the brake system is not coming up to pressure, usually due to either a leak or air in the system.

Did you open the hydraulic system in any way, such as loosening the bleeder screws or removing the brake hose from the caliper? If so you may have allowed air into the system and the brakes will need to be bled. 

Check the brake fluid level in the master cylinder, is it low? Are you losing fluid onto the ground? You may have blown a brake line after disturbing it. Lines can get rusty and moving things around can disturb the bad spot enough to cause a break. Twisting or pulling on an already weak brake hose may cause it to begin leaking.

If you pushed the pedal hard down to the floor while pumping the brakes up you could have damaged either the brake booster or the master cylinder, this isn't common but possible with some vehicles.


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## joecaption (Nov 30, 2011)

Did you bleed the brakes?


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## jonnica22 (Apr 9, 2012)

Thanks guys, yes I just bled all 4 corners with the same end result. I do hear a wooshing sound from behind the brake pedal when I press down, reminds me of when the booster was bad in my bronco.


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## Windows on Wash (Aug 30, 2011)

Did you keep the reservoir topped off or did you let it get air into the system?


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## 1995droptopz (Sep 14, 2010)

The whooshing noise you hear is normal, that is the airflow through the booster inlet. Did you open the system up at all?


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## jonnica22 (Apr 9, 2012)

*disc brakesa drivin me crazy*

Hey thanks you guys, No I did not open the system, I was talking to a mech. friend of mine and he thinks I might have blown the seals in the master cylinder when I pumped the brakes up. any thoughts on this. PS I did have the resivoir cap off during the pad replacement.​


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## taylorjm (Apr 11, 2013)

No idea. Done many pad replacements but never had that issue. I can't see how pumping them up with the car off is going to do anything unless you pushed down hard enough to break the pedal. Did you find any fluid anywhere? Was the cap on tight? You said you bled the brakes, all the bleeders tight and no fluid coming from them? You bled the right rear, then left rear, then right front, then left front, in that order, correct?


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## rustyjames (Jul 20, 2008)

I've done a lot of pad replacements and not once was it necessary to bleed the brakes afterward.


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## ukrkoz (Dec 31, 2010)

Whooshing noise during braking and pedal going down is leaking brake booster diaphragm. You busted it doing pumping without engine turned on. No, it's not "normal" noise.


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## 1995droptopz (Sep 14, 2010)

ukrkoz said:


> Whooshing noise during braking and pedal going down is leaking brake booster diaphragm. You busted it doing pumping without engine turned on. No, it's not "normal" noise.


Not how this failure mode would manifest. It should evacuate all of the vacuum after 2-3 applies with the engine off, then go solid. This could not cause the diaphragm to damage.

If the booster has a leaking diaphragm, you would have an overly solid brake pedal with no vacuum assist. If you have a spongy brake pedal, it means you have air in the system or a leaking master cylinder. It would be very coincidental if there were no soft pedal symptoms before the pad change and the master cylinder failed during the pad change.

I have my money on air in the system, or perhaps a bad master cylinder. If the MC is indeed the culprit, make sure you bench bleed it before installing on the vehicle.

I have 8 years of experience in brake system testing/engineering


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## taylorjm (Apr 11, 2013)

X2. The 2 man way to bleed brakes involves someone pumping up the pedal with the car off. It didn't damage anything. I'm going with air in the system.


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## ukrkoz (Dec 31, 2010)

_If your brake booster fails, you often have a very hard brake pedal. You might still be able to stop the vehicle, but it will require a great deal of effort to do so. The first thing to check is the vacuum line going to the booster. Next, inspect the check valve that might be located in the vacuum line somewhere. Sometimes they're part of the feed line and cannot be accessed externally. If this type of check valve goes bad, you replace the entire vacuum hose. This check valve allows vacuum to go to the booster, but not back to the engine. *When brake boosters fail, it's often a result of a master cylinder failure. Sometimes when a master cylinder fails, it leaks fluid into the brake booster. This can sometimes eat through the rubber diaphragm in the booster and cause it to fail.* Other times, I've seen the return spring in the booster break and rip the diaphragm. *Sometimes you can hear a hissing noise under the dash when a brake booster fails. This is the vacuum escaping. This vacuum loss can also cause engine performance issues.* Either way, the fix is the same: Replace the brake booster.

http://www.ericthecarguy.com/faq/solving-brake-problems?start=7#BrakeBoosterProblems
_


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## 1995droptopz (Sep 14, 2010)

_ The first thing to check is the vacuum line going to the booster. Next, inspect the check valve that might be located in the vacuum line somewhere. Sometimes they're part of the feed line and cannot be accessed externally. If this type of check valve goes bad, you replace the entire vacuum hose. This check valve allows vacuum to go to the booster, but not back to the engine. *When brake boosters fail, it's often a result of a master cylinder failure. Sometimes when a master cylinder fails, it leaks fluid into the brake booster. This can sometimes eat through the rubber diaphragm in the booster and cause it to fail.* Other times, I've seen the return spring in the booster break and rip the diaphragm. *Sometimes you can hear a hissing noise under the dash when a brake booster fails. This is the vacuum escaping. This vacuum loss can also cause engine performance issues.* Either way, the fix is the same: Replace the brake booster._

_http://www.ericthecarguy.com/faq/solving-brake-problems?start=7#BrakeBoosterProblems_




ukrkoz said:


> _If your brake booster fails, you often have a very hard brake pedal. You might still be able to stop the vehicle, but it will require a great deal of effort to do so._


Yes but the OP states that the pedal goes to the floor.



ukrkoz said:


> *Sometimes you can hear a hissing noise under the dash when a brake booster fails. This is the vacuum escaping. This vacuum loss can also cause engine performance issues.*


This is true during steady state. If the pedal is not applied and there is a hissing noise, then the booster indeed has a vacuum leak, the pedal will likely be hard, and the booster has failed.

The noise of air whooshing while applying the pedal is the sound of atmospheric pressure replacing the vacuum in the booster. Perfectly normal. Some vehicles louder than others.


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## garykerr (Mar 6, 2014)

Disk brake contain hydraulic pressure system as well many kind of disk plate are available while pumping the brakes up you could have damaged either the brake booster or the master cylinder and chek the fluid also.


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## Chokingdogs (Oct 27, 2012)

jonnica22 said:


> Hey thanks you guys, No I did not open the system, I was talking to a mech. friend of mine and he thinks I might have blown the seals in the master cylinder when I pumped the brakes up. any thoughts on this. PS I did have the resivoir cap off during the pad replacement.​


you bled the brakes and had the MC cap off, therefore you did open the system. im leaning towards air in it.

im not familiar with that car's brake system, so...does it have ABS? if so, 2 or 4 wheel? is it 4 wheel disc or disc/drum? did you only replace front pads or all 4 if 4 wheel disc?

if its got ABS and you got air in the system, that could be an issue. the solenoids need to cycle when doing that if its not being pressure bled. if it doesnt have ABS, try bleeding again. if you dont have access to a pressure bleeder ( may be able to rent one from a parts store? ), make sure you bleed correctly.

put a block of wood or a small book on the floorboard so pedal doesnt bottom out.
use a clear line on the bleeder screw and only crack it just enough to let fluid run.
whoever is pushing on the pedal make sure they do it slowly, with even pressure.
most importantly, do NOT let the pedal hit the wood/book before you close the bleeder. close it while there's still fluid coming out.
last but not least, keep an eye on the fluid level in the MC, do not let it run down past half full. keep refilling as needed.


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## 1995droptopz (Sep 14, 2010)

Chokingdogs said:


> you bled the brakes and had the MC cap off, therefore you did open the system. im leaning towards air in it.
> 
> im not familiar with that car's brake system, so...does it have ABS? if so, 2 or 4 wheel? is it 4 wheel disc or disc/drum? did you only replace front pads or all 4 if 4 wheel disc?
> 
> ...


Cap removed will not have an affect. General practice when bleeding brakes.

Cycling the ABS is probably not required. During base brake operation the fluid flows from the master cylinder into the ABS unit through the open isolation valves, against the closed dump valves, and then out to the individual wheels. Unless the ABS valve is replaced or cycled with air in the system there should be no need to cycle solenoids.

A block is not required below the pedal. Press on pedal, open bleeder, pedal to the floor, close bleeder, lift pedal. As long as you do not release pedal with a bleeder open there will be no introduction of air.


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## Bob Sanders (Nov 10, 2013)

jonnica22 said:


> Thanks guys, yes I just bled all 4 corners with the same end result. I do hear a wooshing sound from behind the brake pedal when I press down, reminds me of when the booster was bad in my bronco.


If there is no fluid leaking then you blew the MC. This scenario is not at all uncommon on older vehicles.

When you replace the pads you have to reset positions of all the caliper pistons back to their original start position. This forces old and sometimes contaminated brake fluid back to the MC, and it doesn't take much crud to destroy the MC seals.


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