In reply to a message from kenny 91 XJ6 sent Mon 12 Oct 2009:
Ken,
On your '91 Teves equipped car it is not true to say ‘‘that
the pump should only activate about every 5 to 6 times the
brakes are applied’’. The brakes on my car are first class
and if your car performs in a similar manner, the
accumulator sphere is not at fault
Typically, when my car has been sitting unused so that any
residual pressure in the accumulator has long since
dissipated, on turning on the ignition to position (II)
(without starting the engine), the pump motor runs,
the ABS light extinguishes after 32 seconds, the ‘BRAKE’
light extinguishes after 35 seconds and the pump stops after
42 seconds. This timing will vary depending upon ambient
temperature, but is a guide to what you should expect on a
properly functioning system.
With the ignition still on, the pump will re-start, usually
on the second application of the brake (but occasionally on
the first) and run for about 3 seconds to recharge the
accumulator.
Then, with the ignition switched off, it usually takes about
30 applications of the brake before the pedal �goes hard’
when servo assistance is lost.
It is this last check which is the ‘acid test’ for
accumulator condition. If you get less than, say, 15
applications of the brake before the pedal ‘goes hard’, you
should replace the accumulator sphere.
[As an aside, my son’s Range Rover with a Teves system
comparable to an XJ40 system suffered a similar problem to
the one you describe. When I drove it I noticed that the
Teves pump would often run for a few seconds whilst the car
was stationary at traffic lights. That was a precursor to
apparent loss of brake pressure (pedal sinking to floor) for
a couple of seconds when, say, pulling out of a parking slot
signalling the imminent failure of the accumulator sphere.
New sphere fitted and the problem was solved.]
You should also be aware that if you press hard and long
enough on the brake pedal, it will eventually sink to the
floor. That does not indicate that the master cylinder has
necessarily failed because before that happened whilst
driving the car, it would have screeched to a halt in a
cloud of tyre smoke long before that pedal got anywhere near
the floor.
Converting to a vacuum boost system is OK for pre-'90 cars
with the unreliable and expensive to repair Girling system,
but I see no reason to do so on a Teves equipped car. If you
do have a master cylinder problem, converting to vacuum
brake boost ain’t gonna help any! :-)–
The original message included these comments:
The problem that I am having with the brake system is the
pedal intermittently will fade to the floor. I can hear the
pump operating each time the pedal is applied and as I sit a
stop light it periodically comes on. I was just told that
the accumulator is bad and that the pump should only
activate about every 5 to 6 times the brakes are applied.
Could someone please verify this to be true. Another person
as well as I believe the master is allowing fluid to pass by
as the brakes are applied.
I am open to the idea of converting my XJ6 to a vacuum
–
Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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