A3 brake pedal sinks, help please.

[andy10v]

Might as well at this point.

I know collapsed flexis can act as one way valves, do you think it could have collapsed internally then returns to normal size under pressure?

[Monkeymagic]

If they are crushed from clamping they will not re open under pressure.

[bunyoch]

Weel weel noo - the ' forces o darkness' themsells has bin liftet an the Braw Beastie his brakes agin --- an wi nae a richt tirrivee ataw the dey -- jist a last wee stramash frae the brute an a welter o spume oota wan FRONT ? coarner

Ma thanks gang tae aw who assistit in gittin this unner control an tae the 5Litres o brake fluid thet hae passed through its gizzard !

[4WheelDrifter]

Are both rear calipers nice and clean? I have found that the rear caliper carriers corrode and cause the pads to stick, resulting in a long pedal.

[andy10v]

Now sorted, thank you everybody for help, patience and suggestions.

Pressure bleeder at 10psi
Opened all brake bleed screws
Activated ABS pump
Got air out of front callipers
Pumped brake pedal whilst opening and closing front bleed nipples until clear fluid.

Done

What a fiasco

We can only assume an air bubble ran up the rear brake lines into the ABS block and then sat there bouncing about when the brake were bleed, finally dislodged with all bleeders open and the pump running? Whilst it is odd it came out the front callipers, but when you bleed the ABS with VAG COM it only asks you to open the flood bleed nipples during the process so perhaps that is how it is designed to purge?