Brake Pressure Issue

[hans4354]

I've got myself a doozy that I can't figure out - might be something simple that I just haven't learned yet, hopefully someone else has come across a similar scenario ...

 

I have a 2001 Silverado. 5.3L, 4WD, conventional brake system. Far as I know it's been in MN/WI (heavy on the road salt) for its entire life.

 

My issue started with the typical low speed ABS activation. I called the dealer and gave them my VIN and they said the ABS Speed Sensor had been taken care of several years ago. I purchased two new ones and installed.

 

While trying to get my rotors off I noticed that both front calipers were seized up. I proceeded to replace those (along with the worn pads and brackets that I could not get off the calipers thanks to Torx slider pins). After that though, I could not get the system bled correctly.

 

After trying several methods of bleeding (but not the automated bleed using a scan tool) and not being able to build up a pedal with the engine off I decided to replace the master cylinder for two reasons: one was that perhaps the old one was not moving enough fluid to pressurize the system, the second was to fully replace the old fluid that was very dark and full debris (MC had tons of s**t in it) and some of the old fluid most likely boiled due to the seized calipers.

 

Even with a bled MC I cannot get the truck to build up a pedal. It gets stiffer, but seems to reach "peak stiffness" after 7-10 pumps. My next thought is to replace the booster, but past that I (and my father, grandfather, and neighbor...) am STUMPED.

 

Did not push pedal all the way to floor as not to blow seals in new MC. Did not have proper equipment to bench bleed new MC, so it was gravity bled. Absolutely zero leaks, drips, or missing fluid other than bleeding MC and calipers. Not sure how old rear calipers are, but they are not currently seized. Did not use scan tool to run automated ABS bleed (doubting that I got air all the way to the pump). Replaced parts were: front calipers, brackets, and pads; both front ABS speed sensors; MC with reservoir; enough new fluid to fill MC and res.

 

Thanks in advance for any help!