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Discussion Starter #1 (Edited)
I installed new pads and rotors and brake fluid on my 2003 Passat B5. I bled all four calipers after first bleeding the ABS pump using a VAG COM. I believe all the air is out of the system but can't determine why the brake peddle is firm and at the top when the engine is off but sinks to the floor when you start the engine?

I appreciate any help or ideas you may have.
 

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Do the brake pump up higher if you pump them with the engine running?
 

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Discussion Starter #3
Do the brake pump up higher if you pump them with the engine running?
Yes but with even moderate pressure on the peddle it sinks down almost to the floor. Interestingly the brakes hold the car from rolling even with the peddle that close to the floor.
 

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What was your bleeding method? Using the pedal pump and fill technique could allow air to get into the back reservoir compartment if you aren’t careful and frequent on refilling.
 

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Discussion Starter #5
What was your bleeding method? Using the pedal pump and fill technique could allow air to get into the back reservoir compartment if you aren’t careful and frequent on refilling.
A VAG COM was used first to activate the ABS in conjunction with a vacuum bleeder applying vacuum to both front bleeders at the same time, this was done repeatedly. The rear brakes were bled beginning with the right rear followed by the left using a vacuum bleeder on each caliper individually. The reservoir was was never allowed to to go empty and was kept full.
 

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I'd suspect that a seal in the master cylinder failed, considering you've covered all the other bases.
 

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Discussion Starter #7
I'd suspect that a seal in the master cylinder failed, considering you've covered all the other bases.
I agree.... I disconnected the lines from the master cylinder and capped them, a hard peddle with the engine off and running rules out the master cylinder.
 

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There is almost certainly air in the system, I would expect that after using a vacuum bleeder.
Try a pressure bleeder, or use the brake pedal method.

And, don't drive the car until you get that fixed.
 

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Discussion Starter #10
Then there has to something else; a loosely attached caliper that flexes, trapped air, etc.
Yes there is something however at this point I believe air in the system or a loose caliper can been ruled out. I'm going to work on it again today. The only thing I can think of now is possibly tightening up the rear caliper pistons.
 

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There is air in the system.
Put that vac bleeder in the bin where it belongs, and bleed the brakes properly.
 

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Discussion Starter #14
Tomvw doesn't mince words.
We used the VAG COM to bleed the ABS unit. Beginning on the right rear then left rear, right front and left front caliper we used a vacuum bleeder, a pressure bleeder and finally the pump the peddle method. At this point we are simply wasting brake fluid. Please does anyone have any ideas?
 

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Perhaps a piston seal is damaged, either in the calipers (fluid level would drop and fluid would build up in the outer seal or leak) or in the master cylinder. The master cylinder seal can be damaged by bottoming out the brake pedal when bleeding. I've never had it happen to me, but I have read about it multiple times.
 
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