I am currently restoring a 1987 Nissan 300zx

I replaced the master cylinder and when bleeding the brakes the pedal would hold for a few seconds and then slowly fall I ran about 2 liters of fluid through it and determined that the master cylinder was defective and returned it for a new one

I bench bleed the new master cylinder and installed it and ran about two liters of fluid through it my previous issue was resolved but when I hit the brake pedal it is soft but doesn't go all the way to the floor after two-three pumps it feels as it should let it sit for 30 seconds and I have no breaks until pumping the pedal.

There is no fluid leaking anywhere and I am getting clean fluid out of all four calipers (new breaks right around) I have also played with the adjustment on the brake booster and still, nothing calipers are on the correct sides as well

Replaced all flex lines still unable to bleed brakes

  • What does "after two-three pumps it feels as it should let it sit for 30 seconds" mean? Is the brake pedal still soft? Does the brake pedal go to the floor? May 12, 2019 at 21:23
  • after two to three pumps it feels as a brake pedal should once I let it sit when I hit the pedal goes soft but not all the way to the floor
    – Wazy
    May 12, 2019 at 21:24
  • Thanks. Using punctuation in your run-on sentences will make them much easier to read. May 12, 2019 at 21:29

2 Answers 2


Because there are no external leaks and the brake pedal now doesn't go to the floor but (sometimes) is soft, either a) air is still trapped in the brake system, or b) one or more of the car's flexible brake lines has fractured internally, thus temporarily allowing brake fluid to fill the space between the line's two layers. Read the answer posted here.

  • I replaced all of the flex lines and I am still unable to bleed the brakes
    – Wazy
    May 19, 2019 at 15:32
  • @Wazy Then there must be air in the system. Try bleeding using a different method, make sure you bleed the furthest parts of the circuit first. Other than that, I'm out of suggestions. May 19, 2019 at 17:50

reaction disk..... this took way to long to figure out

  • Thanks for reporting back! I had never heard of a "reaction disk" until this discussion. Aug 19, 2019 at 20:35
  • If you pull the master cylinder, it is the part that the rod pushes on in the Booster, and they occasionally go bad.
    – Moab
    Feb 17, 2020 at 23:10

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