Did the master cilinder you are using come from a 4-disc car?
And are you now using it on a front disc and rear drum setup?
Then you need to add a 10 psi residual valve to the rear.
It ensures the rear brake pads do not go all the way back and stay close to the drum. Otherwise you will have a lot of brake pedal travel before it starts braking.
At least that was the solution in my case when I had the this issue.
More details in:
https://www.oudevolvo.nl/english/2019/01/22/testing-tesla-ibooster-power-brakes/
And are you now using it on a front disc and rear drum setup?
Then you need to add a 10 psi residual valve to the rear.
It ensures the rear brake pads do not go all the way back and stay close to the drum. Otherwise you will have a lot of brake pedal travel before it starts braking.
At least that was the solution in my case when I had the this issue.
More details in:
https://www.oudevolvo.nl/english/2019/01/22/testing-tesla-ibooster-power-brakes/
