Viper,
I say this not to be depressing or cruel, but if you own a car from Crewe there will be trouble ahead. The only question is how much. Shadows in particular seem to be "perpetual project" cars even when they are in excellent shape.
Just FYI, you will not ever notice a change in pedal feel in these cars like you do with a conventional braking system. The brake pedal does nothing more than opening a valve to let hydraulic fluid under pressure go where it needs to go. The whole "Oh, heavens, it's slowly (or quickly) sinking to the floor" experience just doesn't happen. That's what makes the potential danger from bad accumulators even worse.
I had posted the prior information several years ago but cannot find it via a search, so I'm posting it again. Doing the "Brake Pedal Pumping Test" is a quick and dirty way to determine if there are issues with the accumulators. If you have your pressure lights coming on in under 30 pumps (and some people would say 40) then you probably need to rebuild your accumulators and accumulator valves. Once you restart the car it should not take any more than 30 seconds for both pressure lights to go out if things are working as designed. However, if they go out instantly then suspect you have a burst accumulator diaphragm.
The formal diagnostic steps are for isolating the location problems in the whole system.
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Testing the Rolls-Royce/Bentley SY Series
[Shadow/T & Shadow II/T2] Hydraulic System
1. Make sure the system is *COMPLETELY* depressurized. The easiest
way to do this is to turn the key to the RUN position *without*
starting the car. Pump the brake pedal 50 to 70 times until the
Brake 1 and Brake 2 pressure warning lights come on. (If only
one warning light comes on after 70 pumps, you probably have
a bad pressure sensor for the system that hasn't lit. If neither
light up *both* are probably bad.) You definitely need to pump at
least 30-50 times *after* the pressure lights illuminate to completely
depressurize the system.
2. Slowly turn and remove the bleed screw on the accumulator you are
testing and screw in a proper pressure gauge.
3. Start the car. In a PERFECT system:
- The gauge should quickly go right up to 1000 PSI. THis is
called the "flick up pressure" and directly relates to the
amount of nitrogen charge in the lower half of your accumulator.
- After the initial flick up the gauge should start rising higher
and higher until it reaches 2500 PSI and stops. This is called
the "cut out pressure".
- The gauge should then drop by about 100 to 150 PSI and then stay
steady between 2350 and 2400 PSI. This is called the "fall back
pressure."
4. Turn the car off. The pressure should now stay steady. If the pressure
drops at this point you have a leak somewhere in the system that could
be internal (some internal valve not closing when it should) or external
(a leaking o-ring in a valve somewhere. You may see dripping or, more
often, a "crust" has formed over time where there is a tiny, slow leak.)
If you've got a leak, find it and get it fixed before starting this whole
process again.
5. Start the car again and pump the brakes or activate the height control to begin using accumulated pressure. The gauge should drop slightly each time. When the decreasing pressure drops to between 1750 and 1850 PSI the accumulator valve will open to begin pressurizing the system again. The pressure at which the valve opens again is called the "cut in pressure."
6. The gauge will then begin rising, going back up to the cut out pressure of 2500 PSI then drop back down to somewhere between 2350 and 2400 PSI, the fall back pressure. *ANY* loss of pressure if there has been no activation of the brakes or height control indicates a leak *somewhere* in the system.
7. If there is a leak, you need to keep isolating the different components until you find the problem.
Some examples of possible problems:
A) System is depressurized to 0 PSI, you start the car and the gauge rises slowly and steadily to 2500 PSI, then falls back to 2350 and holds steady. You turn the engine off and the pressure continues to hold steady:
YOUR ACCUMULATOR LACKS ITS NITROGEN CHARGE.
YOU KNOW THIS BECAUSE THE FLICK UP IS ABSENT.
B) System is depressurized to 0 PSI. Engine started and gauge goes quickly to 600 PSI [flick up present, but low] then rises slowly to 1900 PSI and stays there. Turn off the engine and the gauge slowly falls back.
YOU HAVE AN INSUFFICIENTLY CHARGED ACCUMULATOR AND
A PROBLEM WITH THE ACCUMULATOR PRESSURE VALVE.
C) System is depressurized to 0 PSI. Start engine and a quick rise on the gauge to 1000 PSI [correct flick up] then steadily rises to 2500 PSI at which point it settles bak to 2350 PSI [correct fall back]. When driving the car you feel a clunking sensation that seems like a misfire (but you know the engine isn't misfiring).
YOU ARE FEELING THE BRAKES ACTIVATE WHEN THEY SHOULDN'T. ONE
POSSIBLE CAUSE IS THAT THE SOLENOID VALVE THAT CONTROLS THE SPEED
OF HEIGHT CONTROL IS ENERGIZED AT THE WRONG TIME (CAUSING FAST
LEVELING BEHAVIOR WHEN IT SHOULD BE SLOW). MORE LIKELY, THOUGH,
IS THAT YOU HAVE A PLUGGED UP RESTRICTOR VALVE THAT'S CAUSING
FLUID BACK PRESSURE.
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