[Paulopto]

Hi guys,

I just had a sticky calipper on a bmw f30 and decided to fully rebuild both break calipers myself.

I ordered a rebuild kit fron frentech that fitted like a globe!

After installing the kit the piston seemed to work nice and freely and no leeks after bleeding.

I do have break pressure and the pedal feels nice, however after I press the brake pedal both front caliper won't retract preventing the car from moving even an inch and the pedal goes hard (like when you press the pedal a few times when the car is off)

As soon I released the bleeder valve the pistons retract when pressure is realeased. So, I'm thinking that the calipers are working properly and something is preventing the system to release pressure when I release the pedal.

I have no idea what could be causing it. Any advice will be much appreciated

Thank you

[Alscoob]

Brake servo vacuum leak perhaps? Is there a one way valve in the system and has it been put back on the wrong way round?

[Eddamoo]

You could have a blockage somewhere in your brake line circuit anywhere from the master cylinder to the calliper connector, although the chances of this happening to 2 callipers at once is very low - you may need to go right back in the system.

When you press the pedal, you're generating significant hydraulic pressure to fill the pistons, but when you release the pedal, there is much less pressure to send the fluid back to the master cylinder. It effectively turns into a 1-way check valve and gets stuck.

As you mention, moderate force on a calliper piston should be enough to push it back so the pistons themselves should be fine.

[ushafiq]

Hi, wondering how this issue was resolved?
I am also planning to rebuild my front calipers so any lessons / precautions would help.
Thanks