It seems I may finally have cracked the problem (or was it two, three or four problems?) ....
Problem number 1) - The brake drum assembly seems to be an amalgam of bits, some from the original bike and some e.g. the shoes from a a different or later bike resulting in a bit of mismatched geometry. The result was that (particularly after I had the shoes re-lined) there was very little free movement before part of the shoe made contact with the drum.
Problem number 2) - Another result of the mongrel assembly, the wrong part of the shoe made contact with the drum i.e. the end of the shoe next to the fixed pivot about an inch in from the end of the lining was making contact.
Problem number 3) - There was some wear in the hole of the torque link were it fitted on the stud in the backplate.
Problem number 4) - The non standard (home made?) rear stand fouled the nut on the torque rod back-plate stud when the bike was on the stand.
Numbers 1 & 2 were solved by mounting the shoes on the faceplate of my lathe and skimming approximately a 1.5mm of the nice shiny new shoe away and then using a flat Permagrit tool (wonderful tools, no one should be without them) to remove a little more from the lower, fixed pivot end. The result was that there was some free movement of the arm before the shoes made contact with the drum and subsequent testing showed that the, at first, ineffectual braking power of the shoes due to the wrong contact point was now much improved. Number 4 has been temporarily solved by improvising an extension to the stand stop (a Jubilee clip and washer) to prevent the stand contacting the torque rod nut. This will of course have to be replaced by something a little more sanitary as a matter of urgency!
I think the answer is something along these lines ......
The combination of all four is what caused the brakes to lock up, only releasing when you put the bike on the stand: When the bike was put on the stand the backplate was rotated against the direction of the wheel by the amount of slop (admitedly there wasn't a lot, it was just discernible) in the torque rod bolts. When the bike was in motion with the stand clear of the torque rod nut and the brake was applied hard the backplate rotated in the direction of the wheel to take up the slop. The limited clearance of the shoes and hence minimal free play of the arm resulted in the shoes remaining in contact with the drum even though the brake pedal had been released, not helped by the originally missing springs mentioned previously. When the bike was subsequently put back on the stand to investigate, the backplate was rotated backwards when the stand made contact, releasing the brake shoes allowing the wheel to rotate as if nothing had happened!
Anyway, a reasonably long test ride on suitably deserted bits of road, initially very gingerly, testing both the efficacy of the brakes and checking that there was no tendency to lock up remaining would seem to indicate that the problem is cracked. Having had the wheel in and out approximately 15 times now I can now do it much quicker although the process it is still far from being a work of art. I have to say, at one point Ebay was looking extremely tempting
Alan
