I just finished replacing my calipers, rotors, and pads (3 calipers were seized so I upgraded them all to 5th gen), and I'm having trouble following the bleeding procedure from the FSM, where you pump the pedal 40 times with the key off, then turn the key on and pump another 20 times. From what I've heard, the brake feel should change around the 20th pump with the key off. I think it's supposed to get firmer? Instead, on the 9th-10th pump my brakes lose all pressure and I can push the pedal with almost no effort. If I turn the key I hear the pump running for 20 seconds or so and the brakes feel firmer, but still a little spongy.

Anyone know whats going on here? Can anyone confirm that the brake pedal should get firmer when doing the 40 pumps with the key off?

Forget that. Bleed the rears by turning the key on and open the bleeder screw and it will pump a steady stream, couple of times and you're good. Then bleed the front using the standard push/hold/bleed with key off, or get a Mighty Vac and bleed fronts that way. I always crack the bleeder screw after a caliper replacement and wait until it gravity bleeds and then start the procedure. Never had a problem and my brakes are solid.

Exactly how I did mine, as long as the master cylinder has not had air in it its super simple.

I had this issue for years with my 5th gen calipers. Only thing that fixed it was going back to 4th gen calipers.

Read this thread: Ditching 5th Gen Caliper "Upgrade"

Air gets trapped in the lines to the MC/ABS valve block. Have assistant press brake pedal and crack the lines. Also find a wet road with plenty of room and trigger ABS/TC events to get the fluid in the valve block moving. Repeat as necessary.

I did that when I installed the new calipers, but the brakes are still a little spongy. Not any worse than before, at least. And it definitely stops faster. Maybe I'm just overthinking this.

Crack which lines? I've been planning on finding a dirt/gravel road to trigger the ABS.

My problem isn't with the travel, it's the spongyness, and the fact that I'm not getting the same results from the "40 pedal press" procedure that other people reported. But like I said, I might be overthinking this. The brakes seem to work, but I'm a little worried that there's a problem with my master cylinder (minor leak?) that the brake booster is covering up.

The lines going into and out of the mc/booster block. I think there are four or five IIRC.

I haven't seen the 40 pedal press thing fix any issues I've had in the past. Almost always air in line, bad caliper or stuck pad.

A thought- my pedal also felt "spongy" in the sense that I could basically press it to the floor. Went through multiple bleeds before new calipers finally fixed the issue. Just my two cents.

On the topic of brake bleeding- I'd highly recommend a motive power bleeder. Honestly made a world of a difference in easing the bleeding process. So much easier than having to coordinate with someone holding the brake.

One thing that helps spongy brakes is replacing the flex lines with SS braided.

Crown Performance are the go to brand.

The only reason I'm not convince it's the 5th gen calipers is I had the same problem with the 4th gen calipers.