I found that the brake backing plate for the Ariel hub, can have too much clearance on the axle. This is obvious when the axle is tightened, but with the torque arm removed. Consequently, the shoes will not contact square to the brake drum, if the plate can tilt on the axle.
The plate on my bike had 0.020" clearance (another plate had 0.008", and another had 0.005"). I fitted a bronze bush to the backing plate, with 0.001" - 0.002" clearance on the axle. After doing this, when the torque arm was bolted on to the hub, there was a clearance between it and the mounting lug on the fork leg. I made a thin packing piece to fit, so that when the torque arm / mudguard bolts were fitted, there was no side load on the backing plate; the backing plate fitted beautifully into the hub, and the face of the shoes therefore would be parallel to the drum surface.
Note I have also replaced the felt seal with a lip seal.
Also, With all A and B models, it is worth checking that the fork staunchions are engaged to the same depth below the top of the upper triple tree. Often one is lower than the other (less engagement in the taper), and the lower one can be linished until they both install (tighten up) to the same depth; mine are set 1 - 2 mm below the top. This ensures that the hole for the axle is perfectly aligned in each slider.
Find an automotive or truck brake repair specialist, who can machine the brake drum with the wheel assembled. Sometimes they will require you to rmove the wheel bearings. The fellow I use charges $20.
The front wheel for my '56 RR took 0.012" to clean up.
Get them to also bond and rivet (the rivets are very important; we only get one life!) over size linings to your shoes; the linings will be approx 1/8" over the drum size (7"). Same shop that does the drum machining charges $40 for this, so not too expensive!
Assemble OS shoes onto backing plate, but replace the shoe springs with turnbuckles; I make my own (refer to pics below). Put 0.010" - 0.015" shim packing between each shoe and the actuating cam. This will ensure there is just enough clearance after machining (once removed), for the wheel to rotate freely and safely.
Do up the turnbuckles tight; this locks the shoes square against the cam, and the fixed pivot. The fixed pivot should be adjusted out most of the way, so plenty of adjustment remains.
Make a dummy mandrell same size as axle, and some sort of custom nut, and install (do up tight) the backing plate. When re-using the mandrell, set up in 4 jaw chuck, to no more than 0.001" run-out.
Accurately measure the drum (mine was 7.012" ID after machining), and machine shoes to the same size (tungsten carbide or ceramic tips are best).
File significant bevel (lead-in) on each shoe - at least 10mm long - to prevent leading shoe from grabbing. Wear a mask during all machining and shaping, even though the post- asbestos materials are "supposed" to be harmless.
Remove shims and re-assemble shoes to backing plate, and assemble wheel. Hold brake on, whilst doing up axle and torque arm nut. You will be impressed at the bite even at this stage, because the linings have been arced to the drum, and will be making close to maximum contact.
Remove the wheel several times after short rides, and sand - paper high spots lightly to hasten the bed-in.
Your brake has just got better (but don't tailgate anyone!).
Richard
