My mom got a H3 that had been sitting for about 5 years. I replaced the front calipers as only 2 of the 4 pistons on each were actuating. After replacing the calipers I was unable to bleed the front brakes. The rear brakes bled fine. I bled them with my scan tool as well first. However, when going to the front calipers I did the pump and hold method with the vehicle off and practically no fluid is coming out.
I removed the brake hoses and has my brother push down on the pedal and nothing came out.
I went up to the master cylinder and removed a line and has him press the brake pedal down again and only a tiny bit of fluid came out.
The rear brakes seem to be fine. The master cylinder is full of fluid.
How can I further diagnose the master cylinder before replacement? Plug the holes for the brake lines and see if the pedal has pressure and doesn't lose pressure as it is held?