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soft brakes after multiple parts replaced

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Hi everyone, I have a 2010 MKX and about 3 weeks ago my wife said the brakes feel bad. I thought it was the front pads as I had put a super cheap pair in at the beginning of the year. So I replaced the fronts with some premium pads. Rotors looked good, but I made a note to replace those soon as well. After that, the car felt fine. No issues until the following weekend when I had to slam on the brakes to avoid hitting a person in the road. After that, the brakes felt squishy and needed a lot more effort from the driver to stop. They almost felt like manual brakes. I was hoping that it was the rear pads now, so I replaced those with the same brand/model as the front, and that didnt fix it of course. So I thought it was the master cyl, so I replaced that last weekend and it did not fix it. I bench bled the m/s, and have bled the brakes lots of times and there is no air in the lines. 


Is this an issue with the brake booster diaphragm being ripped? 

Edited by Mustangfreak

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Brake booster failure, definitely.


Same symptoms occurred on my 2012 MKX, including panic stop that yielded hissing noise with a high effort & bottoming brake pedal.


Had mine replaced free of charge under Customer Satisfaction Program 13N02, which may apply depending on your vehicle's build date, per the attached document...


13N02 - Brake Booster Warranty Extension - 2010 thru 2013 Edge and MKX.pdf


PROGRAM TERMS: This one-time program extends the coverage of the brake booster to
ten years of service or 150,000 from the warranty start date of the vehicle, whichever
occurs first. If a vehicle has already exceeded the mileage limit, this coverage will last
through January 31, 2015.


The dealer repair cost charged to warranty was $200 labor + $240 parts.


Good luck!

Edited by Haz
  • Like 1

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I think you will find that you will at least need to bleed the ABS, if booster replacement does not work.  Slowly, the cases for ABS module failure are building for the gen 1.5 vehicles.


Forscan Lite will allow you to bleed the ABS yourself.  BUT you need to follow up and bleed the main system afterwards to completely remove air from the system.  Otherwise they will cycle back into the ABS.


If after all this, you still have soft pedal, replace the ABS module.  Expensive but necessary.  And regularly flush brake fluid.  The ABS components are sensitive to fluid contamination/breakdown.

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I replaced the booster, and it feels much better, but I have a vacuum leak now, and there was a o-ring/gasket that came with the booster, but no instructions, and no clear indication as to where it goes. Where do I put this gasket?


Edit: I'm such an idiot, I figured out the gasket went on the master cylinder. LOL. Car feels back to 100% now!

Edited by Mustangfreak
  • Like 2

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