To get to the bottom of the bore, you have to go around the interconnecting piston rod. You don't have to go that deep tho, just prove the hole is open. That opening you see at the top is not the orifice size at the bottom, rather just the counter bore. At the bottom is a tiny hole, perhaps .020 in diameter, perhaps smaller, I don't recall. I use a single strand of 14ga copper wire which is .011, I think.
If the all drum system is properly adjusted, then without air in the system, there may not be a lotta fluid movement in the lines so you might not get roiling.
All I'm asking is to prove the fluid is returning.
By your descriptions, I believe it is.
If nothing else time and miles will prove it.
however, fluid not returning, unless the shoes are dragging, is not your problem.
If your drums are new and your shoes are new, and if you did not get your shoes ground at a brake shop to fit the drums;
or if one drum is larger than the other;
then the new shoes are going to need a break-in period which could take hundreds of stops, until the shoes are making full contact. During this time if one side has more contact than the other, then you will have a pull.
If you take the drums off and inspect the lining wear, you should be able to see where the lining is glazed and where it is still new. I suppose you could compare one side to the other.IDK, I've never tried it.
The other thing you can do is remove a shoe and fit it to the drum and see how bad it is; if the shoe rocks in the drum, I would recommend to find a brake shop that has the tool to fit your shoes to your drums.
That should cure your pull.
But if a wheel locks up and stays locked-up, that is most likely a fluid-not-returning problem. And the usual culprit is a faulty brake hose. And that is easy to prove. While it is locked up, just crack the bleeder. If you get a stream and immediately the wheel turns, then replace the hose.
But if both sides are dragging, then you need to do some more detective work as it is highly improbable that both hoses fail at once.
