Join Date: Aug 2007
Location: Staunton, VA - USA
Do you have the service records for the car?
The first thing that comes to mind based upon your description is that your accumulators are shot and need to be rebuilt. The fact that the lights both go out quickly suggests, at least, that the pumps are doing their job.
Here's the way to do a fairly exhaustive check of your hydraulic system and to isolate (in most cases) the source of problems:
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 switch for the system that hasn't lit. If neither
light up *both* are probably bad. That, or the lights themselves are
burned out, and you should know whether this is the case or not when
you try to start the car and the warning panel does its "light all the
lights to show you they're working" bit.)
This step is also a "quick test" of how your accumulators are doing
in terms of accumulating pressure. If the indicator light for either
system comes on in less than 30 pumps you can be almost certain
that the nitrogen charge in that system's accumulator is less than
1000 PSI and that the accumulator should be rebuilt. If the indicator
light comes on after less than 10 pumps, you may very well have
a ruptured diaphragm [which basically means that were the engine
to stall you have no brakes for that system almost immediately. NOT
[To complete the "Quick Test",
AFTER BOTH LIGHTS HAVE ILLUMINATED:
1. Start your engine.
2. Observe your warning lights. They should go out after
a. If a light goes out in just a second or two, it's
almost certain that you have a ruptured diaphragm
and the accumulator is being brought up to pressure
by being filled with fluid. If this is the case, YOU HAVE
NO BRAKING IN THAT SYSTEM IN THE EVENT OF AN
b. If they go out after longer than about 15-20 seconds
you probably have a depleted nitrogen charge.
IF EITHER a OR b is the case you need to have your
accumulators serviced. Circumstance 'b' is suboptimal
and circumstance 'a' is downright dangerous.
END QUICK TEST]
2. After you are certain the system is completely depressurized, slowly
turn and remove the bleed screw on the accumulator you are
testing and screw in a proper pressure gauge. Make sure that this
gauge has been used ONLY on RR363 based systems. Mixing even
the smallest amounts of RR363 and the later mineral oil hydraulic
fluid can create a BIG mess.
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
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
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.
The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth. ~ Niels Bohr