2004 Volkswagen Jetta Pistons retract when pedal released

Tiny
PELTIER1234
  • MEMBER
  • 2004 VOLKSWAGEN JETTA
Brakes problem
2004 Volkswagen Jetta 4 cyl Two Wheel Drive Automatic 80.000 miles

All new rotors / pads were installed and the system was bled. Almost full braking was achieved when the pedal pressed to the floor. During the second half of lifting the pedal up front caliper pistons retract maybe 0.3 mm each, I can see these gaps and can insert a paper sheet between the rotor and a pad. When I push the pedal a half way is spent to slose gaps back before it starts braking. Faster pushing or pumping does not change anything. Why I have partial vacuum inside the caliper which pulls the piston in?
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Monday, July 20th, 2009 AT 7:19 PM

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Tiny
DUBTECH
  • MEMBER
It is normal for the pads to slightly retract after applying pressure. This keeps the pads from constantly dragging while driving down the road.
Have you driven the car? How does the pedal feel? If you don't get a firm pedal after the brakes have been bedded in, there may be a problem.
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Monday, July 20th, 2009 AT 9:20 PM
Tiny
PELTIER1234
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The gap is too big and to close that a half stroke of the brake pedal required. I imagine that there is a valve on master cylinder that lets the brake fluid to enter the compressible 'cavity' when the pedal is released (to provide that 'pumping action'). I see on other cars too that this valve seems intently blocked when the pedal starts lifting so partial vacuum is created and the cylinders retract a bit as beginning. As pedal continues to lift the valve lets the liquid under / between pistons and the pad does not retract any more. Other version was the cylinder boot is too springy and it pulls the cylinder back when the pressure is released. But even with new pads when the boot is clearly compressed the problem does not go away. Opening the gap is strictly syncronized with the pedal movement. Do you know anything about that magic valve? If i would design that i would connect a tube with a valve closer to the MC bore dead end. And that symtom would appear if the dead end was drilled too deep! Am I right or just crazy?


http://www.2carpros.com/forum/automotive_pictures/385336_brake_action_2.jpg

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Tuesday, July 21st, 2009 AT 8:35 PM

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