05 Silverado 1500 4x4 Brake Bleeding

[woodja]

Replaced both front brake lines, calipers rotors etc. This truck has front disk, rear drum, ABS.
I cannot get the brakes to pump up. Have bled them with the 2 person method and now using a self bleeder. Have effectively flushed the fluid from the entire system. At least a quart, all comes out clean. Still cannot get it to a firm pedal.
Feels so-so firm after right rear, left rear, right front, left front sequence 4 times. As soon as i turn it on, the pedal drops to the floor. What am i missing?

 

[Mooseman]

Possibly air trapped in the ABS valves. Some have had success driving it on a dirt road and slamming the brakes to activate the ABS but proper way is to get a high end scanner or Tech 2 to cycle the ABS.

 

[Reprise]

I had similar problem when I did the Sierra's brakes recently (had to replace rear calipers, so the system got opened up)
In my case, about 3-5 applications at low speed around the block firmed up the pedal (I then was able to take it to where I always burnish my pads & do that w/o issue.) Pump the pedal before starting out - you should have some vacuum / assist return to the pedal. And I did self-bleeding, FWIW.

It would still be a good idea to bleed the ABS module as @Mooseman suggested (you hold your foot on the pedal while the Tech 2 runs the procedure, and can feel the ABS modulating the pedal... 'so that's what ABS actuation feels like' )

 

[woodja]

Thank you both for the feedback, I'm going to go on the hunt for a scan tool that will electronic bleed the breaks.

 

[mrrsm]

I'm a Year Late getting to the Party on this one... BUT ... For anyone else STILL facing this difficulty:

As per this interesting Video… THIS Relatively Inexpensive Autel MaxiCheck Pro Hand-Held Scanner WILL Perform the necessary GM ABS Electronic System Brake Bleed, and it won't “BRAKE” The Bank or require a GM Tech 2 Scanner:

Amazon is still carrying this Autel MaxiCheck Pro Bi-Directional ScanTool... and... Make sure to Email the Autel People mentioned in the section towards the bottom of the Product Description with your VIN to confirm WHICH flavor of the Autel MaxiCheck Pro is suitable-compatible with your particular Year-Make-Model of Vehicle:

https://www.amazon.com/dp/B075ZLVXHY/?tag=gmtnation-20