Hi,
as a final followup, the brakes are now working fine. I don't think that the problem was wholly due to worn shoes, however I fitted a new pair of shoes just in case and when they are worn out, I'll try fitting the old shoes again.
I ordered the shoes from Old Bike Trader and the part number didn't match the current parts list from SA however the shoes were suitable. The main difference betwen the old and new shoes is the thickness of the actuator cam - you need to replace the shoes with the cam as a set. The new cam is slightly shorter so you don't need the thick spacer washer.
Before removal I measured the diameter of the shoes an three places (trailing Cam - pivot, centre-centre and leading cam - pivot) and the old shoes were 69.93, 69.42 and 69.52 mm in diameter respectively and after assembly, the new shoes were 70.07, 69.94 and 69.86. This shows that there was a little over 0.5mm of wear at the centre point which I don't think is a lot.
I had serviced the brake about 150 miles ago - before the snow and the winter gritting started. I'd serviced it because the brake had started to lock on. I removed the brake plate and removed the cam so I could clean and lubricate its faces and bearing shaft. Due to the construction of the brake, it's difficult to remove the cam without damaging the pivot starlock washer so I removed the cam by rotating it by 90° then opening the shoes a bit more by using a carefully selected nut and bolt as a jack. I was then able to remove the cam and clean it up. It was stiff in the housing and after cleaning and greasing, I released the shoes and found the mechanism much better and the brake worked fine.
I think that my service above was a major factor in my brake problems because it over-stressed the the shoe return spring. When I compared the old shoe spring with the new one, the old spring was a lot more powerful. The area of the spring was the same but the distance between its jaws was different suggesting that I'd stretched it beyond its limit. After riding in the snow and getting hit with road salt etc. the cam and pivots started to seize up and the return spring didn't have enough force to pull the shoes back away from the drum so the brakes were sticking on.
I still don't think they have worn very much - but watch this space for when I have similar problems.
Anyway, back to the service. Below is a pic of the new shoes (I also ordered a spare starlock just in case) :-
- Brake kit + extra starlock
After removing the brake plate, I was surprised at how badly corroded the inside of the drum was - there was a lot of aluminium rust in the drum and on the shoes/mechanism. The pic below is after I had given it a clean - believe it or not, the hub was shiny not too long ago - the winter salts have really take a toll on it :-
- Cleaned up drum
To remove the old shoes, you need to remove the old starlock on the pivot. If you are lucky, it will come of in one piece, if not it will break and you will have to use a new one. I'd advise safety goggles at this point. I couldn't lever the starlock off so I used a screwdriver and tapped it with a hammer. This got the washer off but it pinged a great distance. If you don't have eye protection, cover the washer and screwdriver blade with a piece of rag to absorb the energy :-
- Removing the starlock from the pivot
You should be able to remove the shoes from the pivot and plate now. Mine were corroded on and took a bit of levering with a screwdriver to get them off. I didn't use any release oil because I wanted to see what was underneath, YMMV :-
- Shoe and corroded pivot
after I had removed the shoes, the pivot looked like this :-
- Pivot showing corrosion
Everything was cleaned down - use a wire brush, wire wool and fine emery to clean the surfaces then re-assemble.
Once the brake is locked, I can undo it by pulling the lever hard and letting it fly back a couple of times or I can get off and push the fulcrum back to normal. When it happened today, I was at traffic lights and had to de-clip and rock the bike back and forth to free them.
