From the day I owned this PA50.. the rear brake had this problem... as you applied the R brake... it 'grabbed and released' .. with each wheel revolution... you could hear it go... fwit.. fwit.. fwit.. fwit.. as you rolled along with the brake on.
So I always just let the cable be real slack... so I never got much rear brake action... any tighter and really grabbed during the 'grab' portion.
I figured the drum had a hard spot or something.
Now that I have more speed... I went in there... and found a nice even surface all the way around... nothing to indicate why they 'grab and release' each revolution.
So while I was there I swapped the 2 shoes... (the leading shoe does most of the work and wears faster.. so it is usually thinner... it was).
Put it back together... the old problem is totally gone... I can now adjust the cable tighter and get 3 times the braking force I used to.... great... its nice to have good brakes.
The one unusual thing ?
... the drum construction... it uses a cast iron brake lining cast into the aluminum hub... and instead of the continuous surface... it is C shaped and has a 1/8th split at the ends... it also has a small hole at both ends of the hoop... the split and each hole is filled with aluminum during the casting... never seen that.
But I could not detect a raised edge or anything to 'grab'... smooth as could be... (but the brake shoe could apparently).
And now the problem is gone.... makes no sense to me.. the 'new' shoe is thicker and should grab worse.
But I'm not gonna argue with good luck.