Help! One caliper piston not retracting

[jslagg]

2009 A4 with a sticking (very tight) right front caliper. I have taken it apart, no rust, no tears in boot, caliper moves freely in/out off car... Put on car, bleed & caliper sticks yet if I loosen the bleeder the piston release and the rotor spins freely. I have a new flex line, no change....moved back to the ABS and loosend the rt front brake line at the ABS module and it releases and spins........Would this mean I have a problem at the ABS module or Master cylinder?

Thank you

[Spawne32]

Do you have a vacuum bleeder? Typically thats a sign of there being a clog somewhere in that line, usually at the soft line but you state you replaced it. I would bleed the hard line itself at that side, usually I do it with a vacuum bleeder to avoid air traveling that far back up the system, it may require a few pumps of the pedal to dislodge whatever may be blocking it up.

[Novarider]

If bleeding like spawn suggested doesn't work you cold swap the left and right calipers just to test. It'd be a pain but If the problem stays on the right side you know it's not the caliper.

[Spawne32]

If bleeding like spawn suggested doesn't work you cold swap the left and right calipers just to test. It'd be a pain but If the problem stays on the right side you know it's not the caliper.

pretty sure t hey are left and right side specific and you wouldnt be able to mount them

[flowhigh]

There's missing info here. Is this guy having these problems after a brake pad change or brake lines or something. The rotors should never spin "freely" especially with new pads. The pads are always a bit in contact with the rotor so to speak.

[Novarider]

pretty sure t hey are left and right side specific and you wouldnt be able to mount them

He wouldn't mount them for use. He would swap them just to see if the piston gets stuck like it does on the right side.

[jslagg]

Problem just began, not after ad change or anything, that is why it is very odd. The rotor completely locks up on the rt front.....release bleeder & it is normal, bleed brakes & it will not retract....all other brakes do retract....new flex hose so it must be something in the hard line, right?

[JeriQo]

is it still under warranty?

[dieselquattro]

2009 A4 with a sticking (very tight) right front caliper. I have taken it apart, no rust, no tears in boot, caliper moves freely in/out off car... Put on car, bleed & caliper sticks yet if I loosen the bleeder the piston release and the rotor spins freely. I have a new flex line, no change....moved back to the ABS and loosend the rt front brake line at the ABS module and it releases and spins........Would this mean I have a problem at the ABS module or Master cylinder?

Thank you

This reminded me of the time when I had my A4 (B6) 2.5TDI Avant. I did a S4 brake conversion and it worked really well for a while. Then, I started having the same symptoms as you - one of the front caliper was not releasing completely. Changed the caliper, the brake line, the ABS module and the master brake cylinder (I had an upgraded S4), together with numerous flushes - none of these worked. Eventually, turned out to be the brake servo - there was a split in the diaphragm in the servo, causing it not to release the vacuum completely, thereby holding the one caliper in.

Not sure if it's relevant to you (as it's a B6), but I spent plenty of $$$ before the fault was traced - it may help you get to where you want quicker. Good luck!