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Discussion Starter #1
Break pedal drops in intervals when I press it, nearly to the carpet. It is very very soft.
Break fluid is new and is at good level.
ABS is working ok.

What could be a problem? (main break cylinder?)

Car is:
Suzuki Swift, 2007. year
Engine Gasoline 1.3 litres
Mileage: 55.000 kilometers
 

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master cylinder is bypassing internally. If brakes work fine and no leaks then its the internal seals in the master cylinder. If you press and hold, then release slightly and press again the pedal drops? good sign the master cylinder is faulty, same if it slowly sinks to the floor with pressure.
 

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Yes, all that you write is happening. I'm now sure that is master cylinder faulty and will change it.
Thank you very much.

Today I was at authorized Suzuki dealer and thay told me to change ABS central unit. It costs 2.000 USD! Uhh.
 

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Yes, all that you write is happening. I'm now sure that is master cylinder faulty and will change it.
Thank you very much.

Today I was at authorized Suzuki dealer and thay told me to change ABS central unit. It costs 2.000 USD! Uhh.
do the master cylinder first, if theres no leaks, the ABS unit is acting like a "closed" system and will only control pressure if its actually operating, not when the car is stationary.
 

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Doubt if it is the ABS module, it diverts pressure, does not release back to MC.. until the foot pressure is released..

I would replace the MC, leaking internally...
 

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Doubt if it is the ABS module, it diverts pressure, does not release back to MC.. until the foot pressure is released..

I would replace the MC, leaking internally...
not quite right, under brake pressure reduce mode, the ABS pump will return fluid to the master cyl, this is what causes the pedal pulsations you feel.

Not the issue the o/p has, his is most certainly a master cyl as its stationary and ABS is not operating.

Gurdich, I tried to attach the Suzuki ABS and EBD training document for you to have a look at so you understand how all this works but its nearly 5 megs in size. If you want a copy, send me a private message with your email address and I can send you a copy.
 

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Discussion Starter #7
Today I had conversation with authorized reseller asking them again why to change ABS. Their answer is that is not possible to check where pedal pressure drop, ABS or MC and their opinion is based on experience. On few cars they already change ABS.

Sadly, I not believe them, because it is not professional diagnostic attitude. Probably if I agree they will change both ABS and MC and give me invoice on 2.500 USD :(

Thanks again all you people here for help. Really useful community.
 

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I sent you the training manual and my thoughts as to why the mechanic is wrong and is no more than a parts changer and has not diagnosed it fully.

Change the M/C yourself, simple job, just messy. 2 people needed to bleed the brakes.
 

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Discussion Starter #9
Thank you. Really usefull documentation. I spent last 2 hours to read it carefully and now I am familiar with ABS unit on components level.
If there are faulty inlet or outlet solenoids, warning light will appear.
I am entirely sure that MC is faulty.

@2013GV thank you very much for your time to help and support.
 

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correct in the warning light thoughts, but see how the entire unit is oil filled and once filled fully (hence my earlier comments on making sure its bled properly) theres no way the pedal can go soft as all sides get pressure from the master cyl until it operates when detecting a lock up situation.
 

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Discussion Starter #11
Problem solved! :)

Today I went to another authorized Suzuki mechanic with the same story and with asking them to change MC.
Their answer was that problem for sure is not MC because it never happens on Swift and they claim that problem is with ABS, because they have changed few of them in warranty and out of warranty period. Also they claim that problem in ABS is with solenoids.
I told them that is not possible, because even in case that solenoids are failed, pressure must be the same. There is no leak.

After 30 minutes of discussion, one thing let them think. Pedal sinks allways when braking, not sometimes, and they took car for diagnostic. After one hour they found that one rear wheel brake cylinder stuck. They called me if I agree to change it and after they change it, they bleed the brake system and everything happen to be ok. Pedal is not sinking anymore.

I am really disappointed with both authorized dealers attitude, and also with 1st mechanic that changed one week ago brake oil and did't bleed the system and also didn't noticed that rear brake cylinder stuck.

I assume that they get out some quantity of brake fluid out, and put the same amount of new. Disaster!

My conclusion is that in the system was amount of air bubbles.
 

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air bubbles will certainly account for the issue. As you said the fluid was fine and brakes were ok, the obvious culprit was the m/c.

Glad you stuck to your approach and found an issue and its solved the problem. Thanks for letting us know.
 

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As you said the fluid was fine and brakes were ok, the obvious culprit was the m/c.
You might want to take a second look at that post ...

After 30 minutes of discussion, one thing let them think. Pedal sinks allways when braking, not sometimes, and they took car for diagnostic. After one hour they found that one rear wheel brake cylinder stuck. They called me if I agree to change it and after they change it, they bleed the brake system and everything happen to be ok. Pedal is not sinking anymore.
To my way of thinking, the only way a wheel cylinder can cause the pedal to sink when braking is if it's leaking.
 

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To my way of thinking, the only way a wheel cylinder can cause the pedal to sink when braking is if it's leaking.
or its sticking and slowly moving out and back under pedal application, and the brakes haven't adjusted to it, as in the cylinders moving but not contacting anything. I can see how it could cause the symptoms described, but I haven't seen one do it that hasn't been leaking in a long time.
 

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Been on my mind all day yesterday, was all wired up to a scope (ECG) and they would not let me play with electronics... silly people in white coats...

I am not convinced on the diag... this may be long (attachment), but has your mechanic really checked the system?

 
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