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.

 

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.

 

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.

 

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.

 

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.

 

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

 

How would the use of a vacuum bleeder result in air in the system?

 

Grasping at straws now; any brake hoses expanding while the pedal sinks to the floor?

 

No, all the hoses are in good condition.

 

While replacing the pads and rotors, did you disconnect the calipers from the brake hoses?

 

No.

 

Mine goes to the floor on start-up, but then comes up and works fine. It's been like that ever since I got it years ago.

 

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.

 

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.

So have I, but tend to doubt it. Any design that allowed that to happen would be modified immediately. Liability/recall hazard.

 

It really can only be a bad master or air in the system, and I think odds point to air. I would rebleed using a different method (pedal pump or pressure-bleed) first.

 

I'm a little uncomfortable with "bleeding the ABS pump" through VAG-COM. This should not be necessary on any normal service; I vaguely recall this can damage the pump if done at the wrong time. Anyone else?

 

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?

Brake booster maybe? I think my pedal sinks when I start it, I'll have to try that and let you know. You need to take like 8oz (or more?) out of each caliper when you bleed. So yes you need enough brake fluid. Spend the extra $20 and buy 2 32-oz DOT 4 brake fluids from Advance Auto Parts or somewhere. I used Valvoline DOT 3 & 4 and I bled with speed bleeders (Dorman 12706 - which are basically like check valves) and pedal only. I would crack open a speed bleeder just a little (just enough for it to bleed but not let air back in), then a bunch of half presses on the pedal (don't drive it all the way down - myth? who knows why risk it) and then would have to refill the reservoir so the fluid level doesn't get lower than the reservoir (important), check how much has been bled and I did that many times. You can do it with a tube below the fluid level in an empty bottle instead of speed bleeders. Basically some way so that air can't be sucked back into the system as you bleed. I don't know what's up with your vacuum bleeder. I wonder if you didn't refill often enough.

 

Did you ever resolve this issue ? If so what was the problem ?