I thought the reason for the dual master cylinder was redundancy so that
a rear or front brake failure would not end in total brake failure. This
was a USA mandated safety standard. Mk1 Bs had a single master cylinder.
When I had a small pinhole in my rear brake line where it went over the
axle, I had firm brake pedal like normal (72B, right after a mult-year
restore). However, when bleeding the rear brakes, I only got a small
trickle rather than a normal flow of brake fluid through the nipple on
the passenger rear side. And on a couple of test drives going maybe a
few hundred yards, I noticed my front brakes started overheating, due to
the front brakes doing all the braking. Those were my only symptoms. It
was a matter of determining where there was and wasn't the correct flow
of brake fluid.
David Councill
67 BGT
72 B
-----Original Message-----
From: owner-mgs@autox.team.net [mailto:owner-mgs@autox.team.net] On
Behalf Of Charles & Peggy Robinson
Sent: Thursday, October 12, 2006 2:57 PM
To: Paul Hunt
Cc: John Roberts; mgs@autox.team.net
Subject: Re: Brake Trouble! UPDATE!
I believe the reason for the dual master cylinder in the so-equipped
MGB is that the car has disc brakes in front and drum brakes in the
rear. This necessitates a different size piston in the master for each
type braking circuit.
That being said, I agree that each circuit should have a firm pedal.
My take on the OP's problem is that the rear circuit was clogged up
and the front circuit wasn't fully bled.
CR
Paul Hunt wrote:
> My subsequent thoughts also. As I say I have no experience of dual
> circuit brakes with one circuit failed, but logic dictates that surely
> the whole point of the system is that if one circuit is leaking and
not
> developing any pressure, or is full of air, the other circuit *must*
> give a firm pedal albeit it with increased stopping distances
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