Brake pedal spongy- air in system?
 

Just replaced the front brake pads on my 116 and when I went to pump the pedal to push the pistons against the new pads I wasn't feeling much resitance- then realised I'd left the cap for the master cylinder slightly open- now the pedal is spongy- does this sound like air in the system? And will I need to bleed the whole system? The discs are quite worn and will need replacing shortly, so I was thinking maybe the pads weren't quite bedding against them properly?

When I reversed out of my parking bay I had to use the handbrake to stop the car as I had hardly any power- then I took it for a short road test and it slowly started to feel more normal, but still too much travel for my liking.

It's not worth guessing. Dangerous.

Take it to a shop and have the brakes bled.

New pads require a bedding process. Normally 5 to 8 gentle stops from say 60 mph with time in between to cool.

Normal for reduced braking at initial backout just after replacing pads, but not long.

Steve

i bet you have an empty rear chamber on the master cylinder resorvour.

tom w

450 brakes
 

if both the reservoir chambers are full you will find that you have a wear lip on the rotors and part of the brake pad needs to wear down because the rest of the pad is only lightly touching the rotor.all that you have described confirms this condition.

I agree, that lip can create the impression of air in the lines. Another reason to get the rotors turned, if at least to get rid of the lip.

Where is this rear resrvoir?
Im having this same exact problem on my 300CD accept that theres play to an extent that does nothing. (i can press the brake and nothing happens at all) but once i get to that point the brake catches pretty strong.
Think it might be something with the brake-booster? i tightend a loose conection today and it seemed to help a little bit, but didnt have time to check it out on the road.