2007 classic 1500 z71 dash said "service brakes" figured rears were original (48xxx miles) so I replaced shoes . Same dash warning came up so I checked front pads (replaced 2012) drivers pretty warn so I replaced pads (drums and disks were fine).Now warning light went off ,fluid level is right BUT peddle feels REAL spongy (almost to floor). What did I do? I have changed brake pads on my vehicles for the past 30 years. I would bleed them but how would air have gotten in? I did not breech the system.
Thanks for any help. This is my first time here . I have an older corvette also and have been participating over at corvette forum for years. I'm sure you guys are just as cool

 

I would check your initial adjustment of the rear shoes being a drum brake design.

If too much free play to begin with exists,you will have long pedal travel as you describe.They will only self adjust in reverse,but only if set up correctly.

The front disc brakes are completely self adjusting,of course.