Intermittant hard brake pedal

[ptt]

Sometimes its got a normal pedal.  Can a failing accumulator cause this??

[2seater]

Are one or both of the red or amber lights on? 

[Barney Eaton]

If the accumulator is weak,  it may not store enough pressure for a hard or panic stop.  However under normal driving the brakes feel fine. 

Another possibility is a bad pressure switch... it may be operating (turning the pump on and off) but at the wrong pressures. 

Example the high side of the stored pressure is around 2500 psi.  if the pressure switch is out of calibration (for some reason) as the pressure get low,  the switch should turn on the pump motor around 1200 psi... if it is not turning the pump on until 800 or 900 then you might see a problem with hard or panic stops.

[Jim]

Been a while since I delivered parts to you.

As 2 seater mentioned, the key is, is the red brake light on?

If the red brake light is on you will either need a pressure switch or a pump/motor.

I have both.

[2seater]

The only thing I can share about the pumps and the pressure switches is they are both very reliable, but, it is possible for something to go out of range. I don't have my notebook right at hand, but I have tested many pressure switches and if they do not leak fluid into the electrical connector, they are almost always working in the correct range. IIRC, the red/amber lights should go out around 1650-1700 psi. Those two lights are pretty much the opposite sides of the same switch inside the pressure switch, one normally open, the other normally closed. The actual working range of the system is ~2000 psi (cut in) to 2650psi(cut off). When operating, the pump restarts around 2000psi after the pressure starts to be depleted, and should never drop low enough for the red light to come on. The pressure to make the red light come on while in operation is ~1500 psi, somewhat lower than it takes to make it extinquish. The brakes should still work but would be 25% below the normal low range of the required boost.

[Karlw144]

My system (‘90 convertible) was normal most of the time, occasionally got yellow/ red lights and a hard pedal, and never new when that was going to happen. Had a questionable pressure switch (fluid in the connector body) and replaced the switch. No change. Put a new accumulator on, no more warning lights of any kind, and never a hard pedal again, and the brakes seem to be superior to how the worked previously.