HELP! "I've bled my brakes over and over and the pedal is still soft!"
This is not an uncommon comment and can be brought about by various reasons: air in the system, air in the master cylinder, air induced into the ABS system, wrong piston size selection, deflection issues etc... And we'll assume you already know to only use the bleeders on top and never try to bleed "bottom" bleeders- you knew that already right?? Those bottom fittings are for the top when you mount the same caliper on the opposide side of your disc making it universal fit. (TCE sells blanking fittings for this also)
Some applications however suffer this issue based on CALIPER MOUNTING angles. Nothing more than being mounted onto your spindle at an gressive angle, even on top in some cases. When this happens the bleed passage normally allowing air to be burped from the caliper is too great. That in turn creates trapped pockets at what is now the crown of the piston- beyond the bleed port.
Manufactures have to allow for some of this due to staggered bores or multiple pistons. Often the circles don't line up due to their placement in the caliper body. To account for that the piston bore includes an under-cut or relief to keep the air moving smoothly uphill as it should. But...when you exceed the angle of that under-cut you then have a crescent in one or more piston bores that traps the air.
The solution? Unbolt the caliper and hold it vertically when doing the bleeding. Wedge a board or old rotor between the pads to prevent the pistons from extending and total loss of fluid. (that's bad) When done re bolt the caliper to your spindle; you're good. Note that excessive pedal effort (your gorilla buddy putting all 275lbs of his weight on the pedal...) is NOT necessary for bleeding. Bleeding is nothing more than fluid displacement, not pressure. Your six year old kid is capable of doing this work with you!
In the example image below you see the bleeder passage. On the left the caliper is vertical and all is good. On the right you see when laid over the caliper has created the trapped air described above.