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I have a 2002 Gmc sierra SLT that I just picked up a few months ago. The issue is that the brakes are awful, and they appear to be an issue the previous owners were chasing down too, all calipers, rubber lines, and hard lines have been replaced.

While they do stop, they feel extremely soft and spongy, and go close to, but not at, the floor for just normal braking. I have bled over 1.5 gallons of brake fluid through this thing, with the master cylinder level, raised, and angled down, bled manually and vacuum bled, and I have bled the ABS pump. Any ideas as to what the issue might be?

Edit: Brakes are Vacuum assist also, something that throws me for a loop is that they don't fade

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  • Welcome to Motor Vehicle Maintenance & Repair! Does this have vacuum or Hydroboost power assist? – Pᴀᴜʟsᴛᴇʀ2 Sep 14 '20 at 15:54
  • Amazing after all that, there is still air in system somewhere, which is the primary cause. Secondary might be flexing mechanism such as hoses but unlikely. – Tony Stewart Sunnyskyguy EE75 Sep 14 '20 at 15:56
  • Its vacuum assist, and all the hoses seemed fine, little motion from the rear center line but it wasn't bulging. – Rapsicurio Sep 14 '20 at 16:09
  • Those years had an issue with the abs unit, more than likely you cannot find one rebuilt or otherwise, I bypassed many of the abs units to get a good pedal back. – Moab Sep 14 '20 at 18:45
  • Frankly, I don't think this phenomenon is fixable on that particular model. – EᑎOT Sep 14 '20 at 21:24

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