Mike Lewellen wrote:
> I have a 76 MGB. The dash brake light stays on all the time. PO had
> unplugged it from the bottom of the master cylinder. When is it suppose
> to be on?
It's on when either the emergency brake light is on, or
the PDWA shuttle is on.
The PDWA is right under the master cylinder on most british
cars, so I expect that is what is "unplugged".
Is it still unplugged and the light is on? Or did you
plug it back in causing the light to go back on?
If it's unplugged and the light is on, it's just a LUCAS
somewhere, the usual loose or crossed wires or whatever.
But if you only get the light when you hook up the
PDWA shuttle, the piston is off center.
Briefly, your car has a dual braking system for
safety. If you lose one system, the other still works
enough to let you stop the car with the pedal.
That PDWA connects the two systems with a little
piston in between. If the pressure is lost in one
system, the shuttle moves which cause the light
to come on.
This shuttle also moves during brake bleeding
and other situations. Perhaps the PO didn't know
how to reset it, so he just yanked the wire.
To reset it, you can either take a guess which
side it's on and carefully reset it by bleeding
the other system until the light goes off. (very
slight amount of bleed required, just really
open one nipple and gently squeeze the pedal)
Or, failing that, the shuttle can be centered
with a paperclip. Never tried that myself.
--
Trevor Boicey
Ottawa, Canada
tboicey@brit.ca
http://www.brit.ca/~tboicey/
|