I have attached a drawing of the PH6 series Matco caliper to this note. If you look at this drawing of the caliper it is obvious why we have such a hard time bleeding them. The position of the fluid passages relative to a horizontal line thru each piston hole at the output side will show where and how much air can be trapped. On my calipers the pistons are hollow cups so it makes the trapped air worse. You might want to print out the drawing and then you can position it like your installed calipers and draw a horizontal line on the diagram to assist you in determining how much trapped air you might have and how you might position the caliper to expel the air. Remember to start with the piston closest to the fluid inlet for the positioning. Those with retracts might get good results by retracting the gear most of the way then trying bleeding since the air would move to the back of the piston cylinders. Your mileage may vary! Hope this helps. This is not a design deficiency, just a matter of caliper positioning. Jim James F. Agnew Jim_Agnew_2@Yahoo.Com