Sticky brake pedal?

[BaySundial]

Bit of advice please, when braking and after releasing the pedal it doesn't return quickly and sometimes stays depressed some.
Could this be air in the system? Or something else? Help please!
Graham

 

[Marvel]

How does the brake spring look?

 

[Tintop]

Hi mate

I had this problem, the spring was ok but the medal mechanism had started to seize up. Stripped down, cleaned, greased and put back together. Problem solved.

 

[Harlequin]

Do you have a servo ? if so, that could be leaking causing pedal to stay down especially when braking hard....not cheap replacing a servo.