Strange issue with bubbles in rear brake calipers

Hello to everyone,

This weekend I finally for to replacing brake fluid in my 2009 X5 E70 with 50k miles on it. Well, I ran into something very strange. I started with rear calipers and when they were bleeding, I saw small bubble come out from them together with fluid. Front calipers had no bubbles. But the strange thing is that either before I bled the whole system or after, brakes did not feel spongy at all. Does anyone know what those bubbles in the rear brake calipers were all about?

Originally Posted by igorbmwx5

Hello to everyone,

This weekend I finally for to replacing brake fluid in my 2009 X5 E70 with 50k miles on it. Well, I ran into something very strange. I started with rear calipers and when they were bleeding, I saw small bubble come out from them together with fluid. Front calipers had no bubbles. But the strange thing is that either before I bled the whole system or after, brakes did not feel spongy at all. Does anyone know what those bubbles in the rear brake calipers were all about?

Air bubbles can be devious and stubborn. I always give the calipers a few raps with a small nylon mallet to dislodge them, and start the bleed at the caliper farthest away from the master cylinder.