Not uncommon. The air valve on the remote servo sticks which prevents the
vacuum on one side of the diaphragm from filling, and that keeps pressure on
the fluid downstream of the servo. My roadster has done it for years
intermittently, in hot weather, usually a tap of the brake pedal releases
it. But a pal's was so severe while away touring we had to disconnect the
vacuum hose from the servo and plug it with a spare spark plug.
Some say lubricating the air valve with silicone grease fixes it, others
point to the installation instructions for the after-market Lockheed servo
that shows the servo fitted with the air-valve pointing downwards instead of
upwards as the factory fitted it, yet more say the air valve needs to be
removed and it's cylinder polished with fine wet and dry.
----- Original Message -----
> Wondering if anyone has a suggestion as to what may be the cause of the
> brake servo on my 1977 MGB appearing to come on late and stick.