I have a 2003 VW Passat V6 Wagon. About 6 months ago, I had some work done on the car including Brake Fluid flush. A month later, I had to park the car because I suspected the front bearings went bad because of a loud moaning sound that just got much louder with higher speed.
Anyway, after 5 months of the car just parked in the garage, I had to jump start the car and drove the car back to the shop (a reputable mechanic) to handle the wheel bearings. He replaced the bearings and replaced the battery. And on the way home, after about 30 minutes of driving, I stepped on the brakes and it all the way down (very soft) with no stopping applied. I immediately let go and stepped on the brake pedal again and at that time the brakes were applied. I had to do this everytime I need to apply the brakes for the 5 minutes to get home. The next few days, the brakes behaved properly because my trips were less than 30 minutes long. But anytime the car has been running continuously for over 30-40 minutes, this happens again; brake pedal is soft for the first pump and sort of normal on the second pump.
Brake fluid is clear, full on the reservoir. All brake pads are over 75%, I don’t see fluid leaks around the lines on the calipers. When engine is off, I can pump the brake pedal three times and it is hard and stays up, it will release when I start the engine, so I’m thinking the Master cylinder is OK. My suspicion is air in the lines but shouldn’t that manifest symptoms more regularly rather than only after 30-40 minutes of driving?
Any help is appreciated.