Proportioning or limit valve issue?
 

My A8 3.0tdi 2009 is dragging a rear caliper slightly , but the caliper is not sticky, the problem appears to disappear when towing my caravan.
Can someone point me at the device that proportions brake pressure?
My brake pedal has lots of travel also despite bleeding.....
Suggestions welcome, I have vcds available .
Cheers, Iain.

It is built into the ABS/ESP module as the EBD function, there is nothing intervening hydraulically in between that and the caliper. See SSP204.