After replacing my rear brake caliper i proceeded to bleed brakes. Sounded simple enough. Rear right, rear left, front right ect. Afterward, I had no pressure. i blead again and again. First time w/ helper, second time with cheap vacume, third w/ i borrowed a better vacume. Last time w/ mechanic friend with a very nice set-up (who was beginning to think i was an idiot). He looked at the caliper, and thought they may have gaven me a right side caliper instead of the left. The right will fit on the left side. The problem is that the valve ends up on the bottom when you install the right on the left side. When this happens, air is stuck in top half of piston, and you can't bleed the brakes. Lesson learned! I hope some ones read this before they bleed their brakes four or five times.