Ford Expedition spongy brakes

[leigh]

Hello, I have a 98 Ford expedition that I'm having brake problems with... Front calipers went out so I've had rotors, calipers and brake pads replaced, went to bleed brakes and found both back bleeders were rusted and stuck, eventually got 1 bleeder out/ replaced and other back caliper replaced also, then bled and had no brakes, replaced master cylinder, bled several times, still have no brakes... did some research online read it could be booster so following web directions on checking for booster working properly, pumped up brakes and held, turned in truck brake pedal fell, is this the correct way to check booster? also read it could be air in abs/hcu, have bled brakes several times around, and pumped pumped pumped brakes to no avail... I'm at a loss on what else to do, can not afford to take it to a shop trip be looked at... ANY suggestions will be greatly appreciated and welcomed please!

[ProTech]

It could be air in the ABS pump, and this usually requires a special procedure with a scan tool to get it to bleed out properly. If you cannot get all the air out of the system by normal means, you would have to take it to a shop to have this procedure performed.