2013 MkX - Brake booster Issue

[jpw501]

So my 2013 MkX was one of the lucky few that were involved with the faulty power brake booster recall. The original booster would leak, so much that you could hear it hissing under the hood! Then if you had to hit the brakes after just making a stop - like if you pulled away from a light and someone ran the red opposite you and you had to panic stop - the vacuum would be gone and you had to push hard like manual brakes!
Anyway, the dealer changed the booster about 2 yrs ago - no charge, no big deal worked fine. Lately, I'm noticing about 10-15 minutes after shutting off the vehicle, or leaving it overnight, when I push the brake pedal to start, the pedal is very hard as if there's no vacuum left. Normally the booster should hold vacuum for a long time - at least overnight! Had it at the dealer again and they said they couldn't reproduce the problem. I know it's not me going crazy and there should be a normally light pedal when I first start in the morning. Has anyone experienced this and what did you do to fix it? I think they'd replace the booster again at no charge, but they'd have to 'see' the problem. Thoughts?

Thanks,
Joe

 

[CARR142]

Yes that sounds similar to my 2011 MkX. I had to wait months until it got worse. Booster eventually started to hiss before dealer replaced under warranty.

 

[jpw501]

The saga continues>>> So, I suspected that the vacuum hose might be leaking (slowly) but never got into it to see what was going on. OK, so I'm a procrastinator. A dead battery not only forced me to get under the hood but also allowed me to see the vacuum tubing. What I found was disturbing. The hose runs between the engine vacuum source - a large rubber hose - to the check valves on the booster plug, and then back to the intake side of the MAF. I assume that is a vent in case any crankcase vapors escape and get into the vacuum line when the engine is off, so it doesn't vent to atmosphere. (the horror!!) Anyway, I found that the source end fitting has electric tape wrapped around it and the clamp that is supposed to be pushed over a pin sticking out from the fire wall was instead, not fastened but just floating. So, had the fitting cracked or been damaged when the dealership replaced the booster, hence the tape? Maybe, but does that explain the leakage of vacuum over time? I don't know since the check valves should be holding vacuum in the booster. Is it a combination of things going on? Maybe... I have a replacement vacuum tube on the way (Part No. BT4Z-9C490-B) and I'll update this posting when I get it replaced. Stay tuned.

 

[jpw501]

PROBLEM SOLVED! Yeah, it was the check valve(s). I finally replaced the vacuum tube assembly - which was pretty easy: take the battery out - and immediately on start-up I could tell things had changed. The engine idled smoother and seemed quieter. The test drive revealed that indeed the drivability issues were gone. No more bogging/lagging as the go pedal was pushed!

Finally the big test, after letting the car sit for an hour I went out to test the vacuum leak-down. I stepped on the brake pedal and EUREKA!! still vacuum present! As I drove the car around after that start it seemed to get better and better as the computer figured out it wasn't dealing with a vacuum leak anymore. Idle was smooth. The engine really did seem quieter, and most importantly, driveability was back to 'like new' again. Power was there again both off the line and on downshift.

Amazing what a little vacuum leak can do to mess up your car... Now, if I can just fix my procrastination tendencies! LOL!