[ROVERNET - UK] SD1 brake failure switch

[Gavin.Walker at csiro.au]

Hi Everyone,
  I'm having trouble with the brake failure switch on my 1982 SD1.  This
is the switch that screws into the underside of the master cylinder.
The switch itself seems fine, when I remove it and press it the warning
light goes off.  There are rust coloured deposits on the plastic switch
which suggest that part of the master cylinder may not be that pleasant.

I inserted wire into the whole and in the master cylinder and it can go
in 5mm further than the switch length.  This suggests the piston in that
side of the cylinder is stuck.  I considered undoing the nut at the end
and trying to "knock" the piston loose but the diagram in the manual
seems to indicate this would let the fluid out and I'd have to bleed
them again.

Anyone got any suggestions?  I don't really want to pull the master
cylinder down.  The car has been more or less inactive for the last 5
years.  I changed the brake fluid last year and fixed a leaking flex
line in the rear system.

Thanks

Gavin Walker
Canberra, Australia