Bubbles when bleeding rear brakes

[igorbmwx6]

Has anyone out there tried to replace brake fluid on BMW X5 E70? For the first time, following all the instructions, I replaced brake fluid on my X5. Started with rear passenger wheel, then switched to rear driver's, then front passenger and finally front driver's side wheel. All went smoothly; however, when I was bleeding rear passenger's and driver's side wheels (basically rear brakes), I saw a lot of bubbles coming out of the caliper bleeder as I opened it up (loosened the bleeder screw). I did not see any bubble for any of the front calipers. Is this normal for rear calipers to bleed brake fluid together with bubbles? Physically I do not see any issues, brakes feel good, quick response, just like new. Any feedback on this would be greatly appreciated.

[335i_4D]

Bubbles means you had air in the system at one point.
Could be when the'y replaced the pads, and had a hard time backing the piston. Some mechanics will open the bleeders to back up the pistons.

Usually, with some air, you'll feel the brake pedal going further down.
When there's more air, it feel like you're pressing on a sponge when braking.

When you did bleed the air out, have you noticed the the brake pedal was stiffer, less requested to press on it to actually have a good grip ?

[igorbmwx6]

Well, no. Actually, before I bled the brakes, they were working and feeling just fine. After I bled them they also work and feel just fine. That is what's puzzling me. I understand the concept and I do understand that if the bubble were there, brakes should have felt like sponge, but they did not before and did not after. Also, why there were bubbles in the rear calipers and none in front? Very strange.

[335i_4D]

Like mentioned, if the brake pads were replaced in the rear, maybe the only point where they had to bleed to back up the caliper piston...
Air won't get in the system by itself.
If it does, you have another problem.