line lock on 73 duster ?

AJ/FormS said

If you apply the line-loc button first,then you are preventing brake-fluid from going out to the front system.So if you then step on the pedal, the fluid cannot move, and the pedal feels rock hard. That would be normal.And since the piston in the M/C cannot move, you would not have any brakes at all. Also normal.

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Mine allows fluid to the brakes when applied but not back until released.
I can hold the button down and touch the brakes and the car acts completely normal and starts slowing, then touch the pedal again and it brakes more, but it only lets go of the brakes when the lock is released.

Point is that it is not a solid stop of the fluid both ways, though I'm not sure what any benefits of that function would be.