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Discussion Starter #1
Good afternoon All,

I have been a longtime lurker and greatly appreciate the wealth of information available on these forums. I am a happy owner of a 2015 Q50 premium with deluxe touring and tech package. Purchased the car roughly 16 months ago certified and currently has 46k miles on it.

I noticed the other day that as I sat at a red light the brake pedal was slowly sinking with just enough pressure to hold the car at the light. The motion is slow but steady however it is disconcerting nonetheless since it is the brakes.

Recently took it to the dealer and was told that this is normal behavior but I am not convinced. Has anyone experienced a similar issue?

Thanks!


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2017 Q50 Red Sport 400 RWD
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I don't think this is normal and sound like there is not enough pressure in the lines. Did you have a brake fluid flush/change lately or any work done to the brakes? How's the fluid level? How does normal braking feel?
 

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Discussion Starter #3
I don't think this is normal and sound like there is not enough pressure in the lines. Did you have a brake fluid flush/change lately or any work done to the brakes? How's the fluid level? How does normal braking feel?
Had a pad replacement about 5k ago by the dealer. No flush or any other brake related service. They put it up on the lift yesterday and didn’t see any leaks and the fluid level remains normal.

I’m thinking the pressure loss is happening either at the master cylinder or the ABS actuator but they seem to disagree.


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If the fluid contains moisture (not uncommon for brake fluid, as it's hygroscopic except DOT 5, or another words attracts moisture) or any air or has been contaminated, etc. it will be allowed to compress and the hydraulics won't work properly...this will cause a low pedal or lack of pressure so to speak. Low fluid may also contribute...Check the MC cover to be sure it's sealing properly and not allowing air or moisture.

To a small degree the 'normal' pedal will go down just a little the harder you hold it, although not to the point of it seeming to be concerned.

My suggestion would be to flush the brake fluid/breed brakes and fill with a high quality DOT 4 synthetic, or similar (just don't put DOT 5, as it won't mix and will cause other issues)...that is after verifying 0 leaks.
 

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2017 Q50 Red Sport 400 RWD
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^ Good idea. Time for a fluid flush.
 

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Yeah, my money is also on the brake fluid line. Flush or bleed it.
 

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Do the flush first but that is also typical behavior of a master cylinder with an internal leak. Brakes are too important. Get it addressed soon.
 

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Q50 2.2d sport
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Sure there is a issue with the masters have a dig on google. I have saw this info when doing my research before buying one. But I agree bleed first.
 

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2018 Q50 AWD Red Sport
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Leak, followed by bad master cylinder. Sounds like fluid passing by the piston (what ever it's called) debris in the fluid is usually the culprit.

Air in the fluid would just be spungy. A soft pedal. Sinking pedal is a problem. Losing pressure. If no leaks the master cylinder sounds like the problem.. But it's cheap to bleed and flush first. Maybe air in the ABS can cause this?
 

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Discussion Starter #10
Taking it back in next week. They want to spend a day trying to diagnose it. We will see. My inclination is also the system is not holding pressure. The lack of fluid loss makes me lean toward an Master Cylinder leak however I’ll ask that they do a flush while I am there.


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2018 Q50 AWD Red Sport
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Looking forward to hearing what the problem really is. Please post when it's fixed.👍🏻
 
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