Originally Posted by werminghausen

Hi Au,

Rock hard pedal meaning you had no brake booster at all.
You have a leak on the pressure side
In lack of a technical diagram of the unit it is unknown where the leakage might be located
1)hydraulic 3-cylinder pump/check valve being part of the pump so that pressurized fluid cannot flow backward,
2) accumulator super low on gas (cannot store much energy meaning any leakage is amplified by a weak accumulator) ,
3) downstream a potential leak on the pressure side toward the master cylinder.

Unfortunately I don't have any better information.,

Can you do these quick tests and see how well your system responds once pressurized?

test1:
Key in ignition position
press the brake pedal 3 times as a start.... after how many brake actions
does the motor come on. After 1, 2 or 3 pushes?
For instance after every second push you'll hear the motor. So you push 2 times...brake motor.... push 2 times...brake motor.

(my T4R has the 1-2 pattern. Every second pedal action the motor comes on)


test2
Key in ignition position
Push the brake pedal more often... say 10 times.
Does that trigger the low pressure alarm (all 4 dash lights plus alarm sound)?

(I can trigger the alarm after 6-8 pedal actions)

These tests don't tell you how leaky your pressure side is because these leaks are relatively slow - you said it takes overnight for all pressure to leak out.

But it can tell you probably about the basic condition of the brake health.

I am sure you will get rid of your symptoms with a new unit.
Martin