On Fri, 24 Jan 1997, Mark Moburg wrote:
> the piston
> itself ~must~ block the flow of fluid;
Sorry if I stated this in a manner that could be misunderstood, but the
piston does of course block fluid from one circuit from entering the other
- indeed a piston seal, if broken, would cause brake fluid to leak via the
PDWA contact entry.
But my point is that the PDWA does not block the fluid flow in the
"offending" circuit, as has been claimed.
The reason that you will have braking power if one circuit fails
completely is due to mechanical action in the main cylinder: two pistons
connected in series, and the failing circuit bottoming out.
Although I have never experienced it, I would assume that a sudden failure
in one circuit might require a pump or two one the pedal to restore
pressure on the good circuit.
Be warned that on a simple front/rear split system like on the Triumph, a
failure in the front circuit will leave you with only approx. 1/3 to 1/4
of the original braking power. Also, locking the rear wheels (only) at
speed will immediately cause the vehicle to turn around 180 degrees. But
it is definitely much better than the alternative: handbrake only.
Re. the usefullness of the PDWA - my personal experience is that it is
quite sensitive, and that even a fairly small leak will show up on the
lamp if braking hard. A fluid level warning is also useful, of course, but
in my experience (Jaguar, Renault) these usually stop working after a few
years.
Egil
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