I changed the front brake pads on my car this morning.

Three of the pistons compressed fairly easily using a $3, 3" C-clamp. The fourth was a real bear. I ended up using a 12" lever arm on the C-clamp in order to get enough torque to compress the piston.

I did have the bleeder screw open.

Any idea as to why the piston was so hard to compress? Does it indicate a problem?