Secondary Master Cylinder knocking

I have recently noticed a slight knocking noise from my bike and have traced it to the Secondary Master Cylinder arrangement. With the bike parked up I can move the mounting bracket forwards and backwards which results in the knocking noise - it's as if there is some sort of free play. Could this be due to a lack of 'pressure' or an airlock in the brake line that runs from the Secondary Master Cylinder through to the Servo Proportional Valve and then on to the rear brake caliper? If anyone has experience of this problem then it would be good to hear how you sorted it.
:sour:

 

I have not heard a knocking from either of my VFRs but I have read and seen a few post where the SMC has been problematic. Usually a rebuild of the unit took care of the issue. You might try bleeding the lines and/or taking the SMC apart to see what it looks like inside the unit. What year is your VFR? and does it have ABS? There are two PCV's on the ABS model BTW.

 

I have had the SMC internals replaced with a genuine Honda service kit but there still seems to be a bit of a problem with it. The bike is a 2003 A3 ABS. I am looking to take it to another mechanic to see if they can sort the issue by bleeding the lines between the SMC, the 'rear' PCV and the rear caliper. My thoughts are that there is little pressure in the line from the SMC to the PCV which allows the SMC to rock on its mounting bracket with some free play rather than moving against a constant resistance. Hope this makes some sense.
If you have ant thoughts then I would be glad to hear them.