Pedal may also not be allowing the piston to come back far enough and so clear
the bypass hole, could also be a partial restriction anywhere in the system.
Don't know about a TR3 but on a 4-cylinder MGB getting to the master side of
the slave flex hose is a pain to slacken it off and see if that makes the
pedal suddenly return, probably easier to slacken the banjo union on the
master. If one or more places along the hydraulic circuit makes a difference
then the restriction is on the master side of that point.
----- Original Message -----
Is there a section of rubber hose involved in the hydraulics?
Hoses can and do deteriorate, can soften and swell inside,
often acting as a one way restrictor valve.
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