[Mgs] Brake failure - What caused it?

[Richard Ewald]

I suspect that the rear wheel cylinders are leaking explaining the
loss of fluid in the master, and the seal for the front brakes is
bypassing quite possibly due to corrosion in the master causing the
pedal to the floor.
Rick

On Tue, Aug 24, 2010 at 7:35 AM, Paul Hunt <paul.hunt1 at blueyonder.co.uk>
wrote:
> The whole point of dual circuit brakes is that if one circuit fails the
> other should give some stopping ability.  According to the books the rear
> reservoir supplies the front brakes, and the front reservoir the rear.  So
> with the apparent loss of the rear brakes *only* you should hardly have
> noticed any difference, which implies you lost the fronts, in not both.
 The
> second symptom of loss of a circuit is a longer pedal, but not so long it
> hits the firewall (or what would be the point?).
>
> The only reason master cylinders should need topping up is as the pads and
> shoes wear, and the pads and pistons gradually move out of their own
accord,
> and you adjust the rear shoes and handbrake which likewise allows the slave
> pistons to be at rest further out.  An empty reservoir implies a major
leak,
> which is one problem, and brake fluid dries, even if it falls in a visible
> place.
>
> On a dual circuit system the brake lights are operated directly from
> movement of the pedal, which has no bearing on whether operation of the
> pedal develops hydraulic pressure to apply the brakes or not.
>
> It what you are telling us is correct, I'd say the master seal for the
front
> circuit is highly suspect, sometimes sealing and sometimes not, which would
> be a second problem.  That, with an empty rear reservoir, could explain the
> first 'pedal to the floor', but not the second unless *both* master seals
> were failing, which would be a third problem.  It would be a heck of a
> coincidence for both to exhibit the same failure mode so close together ...
> unless the rear circuit isn't working at all and you have been driving for
> ages on the fronts only.
>
> Remember the adage "Just because you have discovered one problem, don't
> assume you have discovered the only problem".
>
> PaulH.