2000 chevy blazer, brakes pump up good with engine off, but pedal falls to the floor when I start the car

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There is no brake booster with the engine off, there is with the engine on, so it is normal to get more pedal travel with the engine on, but not all the way to the floor. Start with this:

  • Check your brake fluid level, it may be too low
  • Check your braking lines for leaks. Most common leak point is at joints between the steel lines and the rubber lines, as well as near the rubber lines and the brake hardware (calipers, drums)
  • Bleed the lines for air. Air trapped in braking lines causes brake pedal softness.
  • Check the level of brake wear, especially the rear. Worn brakes need more pedal travel.
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