[ROVERNET - UK] SD1 brake failure switch

Nathan Obuch nathanobuch at yahoo.com
Tue Aug 8 04:09:26 BST 2006

    I have not had experience with SD1s, but with dual
master cylinder MGBs, there is a pressure differental
piston in the master cylinder which shifts forward or
back if there is an imbalance in the fluid pressure
between the rear and front brakes. You probably
tripped the pressure differental piston when you bled
the rear brakes. You can probably recentralize it by
partially opening a bleed screw on the front brakes
and depressing the brake pedal until the piston is
centralized, then reinsert the switch. If air gets in
during this procedure, you may need to re bleed. 

       Best of luck,

--- Gavin.Walker at csiro.au wrote:

> 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
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