Can't help with a brake joint but I did have exactly the problem you described. New shoes, new cylinders on the back drums on an old heavy Ford then started dragging the left rear. After much head scratching I found it was a partially blocked rear flexible brake hose (body to hard line across the back of the diff). Pedal pressure was enough to actuate the cylinder but the return springs on the brake shoes were not strong enough to pull them off the drum once you took your foot off the pedal. May not be the solution to your problem (why it only mucked up my left rear and not my right as well??) but it sounds hydraulic ( dickie hose, dickie wheel cylinder..only working front shoe,etc) rather than mechanical (return springs put on wrong, hand brake self adjuster playing up,etc). Happy hunting!

Warren thank you so much for the detailed information, suggestions and for recommending Hitech!!

I know exactly which flexible hose you are talking about and the last time I was under there it was looking worse for wear, a great place to start I think.

On the weekend I had my son operating the brake pedal and can see that both pistons are working on the wheel cylinder (what I failed to check was the return of the pistons now that I think about it...) so I'll take a look at the state of that hose.

Many, many thanks once again. Really helpful stuff, I'll let you know how I get on!