Brake pedal goes to the floor after replacing Master cylinder

  • 3.5L
  • 6 CYL
  • 2WD
  • 163,000 MILES
New booster, new master cylinder. Brake pedal still hits the floor after car is turned on. Brakes have been bled ten times. New fluid new pads. What am I missing? Car has sat for two years without being run.
Sunday, March 24th, 2019 AT 6:23 PM

2 Replies

  • 33,783 POSTS
You don't have to bleed at the wheels when replacing the master cylinder. Doing so might have made the problem occur. Was the new master cylinder bench-bled before it was installed? If not, there is going to be a lot of air in the system. If it was bench-bled, stroking the brake pedal less than about a quarter way to the floor multiple times will wash any air bubbles at the top of the steel lines back up into the reservoir.

If the system was bled with a helper who pushed the brake pedal all the way to the floor, something all professionals avoid at all cost, air would have been sent down the lines, and if the car has anti-lock brakes, it became trapped in the hydraulic controller. To bleed that air out, you'll need a scanner that can access the ABS Computer. It will walk you through the steps that just take half a minute or less. Typical for most cars, you'll be requested to open the two right bleeder screws, then press the brake pedal when prompted to do so. The scanner will command the computer to open two valves so those chambers can be bled.
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Sunday, March 24th, 2019 AT 8:26 PM

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