I have a Saab 9-5 2011 that has a problem that my dealer seems to be unable to address. From time to time, when I depress the brake pedal and then release it, the pedal does not retract to its original position. This does not happen all the time, but when it does, I have to pull with my foot on the brake pedal in order to release the brakes. The dealer has changed the master cylinder and the brake fluid, but the problem continues to persist. I noticed that this problem is more likely to occur if I go backwards. I also noticed that if I park my car, turn off the engine, and pump the brakes, the problem disappears for a couple of days. Does anyone have any idea what else can my mechanic look at in order to address this issue? This is quite frustrating. Thank you for any helpful advice that anyone can offer.
Check the condition of all the rubber hoses that connect to the brake calipers.
A swollen hose will allow fluid under pressure to fill the cylinders and provide braking, but not allow the fluid to easily return.
Beleive it or not, it is merely the square o-rings on the caliper cylinders that tilt slightly and provide the pressure to pull the pads off the rotor.
Weak internal master cylinder springs could also create the same issue, but you indicated you (or the dealer) changed that.
I would inspect the hoses for any soft "gooiness" or sign of collapse. Fluid pressure in lines and hoses may approach 1000's of psi, but the springs and seal that "suck" the fluid back have forces quite tiny in comparison. Debris in the system might also create the same problem (e.g. rust) but I predict it's far more likely a bad flexible hose.