I replaced the calipers, rotors, and pads on a 2007 Pontiac Grand Prix. I'm trying to bleed the brakes and I'm having trouble. I've got a Mityvac brake bleeder and I'm starting on the passenger side rear and I'm not drawing any fluid from the master cylinder brake reservoir. I'm wondering why. Can anyone help?
Is the car on the floor? Many vehicles, I'm not sure if yours does for certain, feature a brake bias apportioning valve which is essentially a "tap" which opens or closes depending on the position of the rear beam axle. If the car is heavily loaded (i.e. has people in the rear seats and a boot / trunk full of cargo), more braking force is sent to the rear wheels.
Problems can occur if you try and bleed brakes with the car jacked up and the rear wheels not touching the ground as this system can be tricked into thinking there is no load on the rear at all thus shutting off the rear brake circuit.
Another possibility is that the car needs to be plugged into a diagnostic computer to tell it that it's brakes are being bled in order to open the ABS lines. However, as you say you bled the front without issue, I suspect the bias valve.
Bleeding the brakes is a 2 person job. One to open and close the valve at the caliper and another stepping on the brake pedal to force the fluid out.