Wally, just a little fodder for thought.
Your thought process on the plunger not fully retracting is a good possibility. Can you take and post pictures of your setup as well as provide info (if known) on vendor and parts used in your system???
Some dual reservoir/circuit master cylinders come already internally equipped with residual valves. If your master cylinder has functioned normally for some time, such residual valves may have no bearing on the problem. If the problem has been on-going since you installed and started using the brakes regularly, they could be part of the problem???
That being said, maybe there is a way for you to remove the existing pushrod, shorten it (while leaving whatever length adjustment ability exists to make up most if not all of the removed length) to create a rod that actually allows for said length adjustment???
See attached screenshot of one of the common aftermarket kits that shows the actuating rod.
In my mind you could unscrew that rod from the spherical joint connector, cut say 1/4" off the "threaded" length of the rod, use a die and extend the locking nut threads farther out on the shortened rod by the same amount, then put it all back together with the rod screwed deeper into the spherical end to reduce the overall length. When that is done, you could then adjust the length of threaded rod to where it needs to be (in bare contact but not forcing the pistons forward) and lock down the nut to maintain rod length??? Just thinking out loud here.
We need more info to brainstorm this theory of yours.
Dan
