Why will my clutch not pump up?

I have seen this a lot of times, especially on Ford Rangers.. The problem I encounter is that part of the line that goes from the clutch master cylinder to the slave cylinder has an upward loop in it somewhere .. This is where the air likely becomes trapped. Air will accumulate in the highest point and usually will be in the plateau of that loop. Once it is trapped in that loop it will not be able to move down through fluid that is below it in a lower section of the line, no matter how much you try to bleed it out.. What you have to do is remove the clutch master cylinder but leave the line connected. If there is anyway possible to straighten up the line without getting a kink in it then that is what I would try.. With it straightened and no upward loops in it then try and pump the clutch master cylinder up by hand while keeping any loop out of the line. You can insert a screwdriver in the back of the clutch master cylinder to depress the plunger while someone opens the bleeder on the slave.. I know it is a lot of trouble but I have seen great techs spend hours and hours trying to rid the air from the system.. If you do not have a upward loop in the hydraulic line then you may have a defective slave or even the new master cylinder could be the culprit. Parts from China and Mexico are just about the only thing available any more and usually several times a week I get a defective part right out of the box.. Best of luck ! Chuck