July 12, 2003
Sturmey S3C teardown
So I bought this wheel on eBay (the only thing I've ever bought on eBay). I was mainly interested in it for the hub, a Sturmey-Archer S3C 3-speed coaster-brake hub. (S3C=Super Cool Coaster Component, not to be confused with its predecessor, the TCW, otherwise known as The Crappy Wun). This would make an ideal rear hub for my chopper.
(The TCW has a bad reputation because the braking action is dependent on the hub being in gear; if the hub is incorrectly adjusted and you end up in the false neutral between 2nd and 3rd, your brake won't work. This could be Very Bad. The S3C has its own problems (Sheldon Brown hates them), but it's at least better than the TCW. (Vomit has an S3C built into her chopper, CFT JanBrady.) The best coaster-brake hub Sturmey made was the AWC, which is based on the venerable and ubiquitous AW.)
One problem: the brake didn't work. Soon after I got it I tore down the brake-side of the hub and discovered that this one was missing its brake shoe. No problem; Broadway had one in stock. So I bought a new brake shoe and installed it, but the brake still didn't work.
So today, I tore the whole thing down.
Pulling apart a Sturmey hub is a whole lot of fun. Once you get past the anxiety and the idea that you'll get a bunch of little springs and gears and things bouncing and flinging off in all directions (which you won't), you're OK. It's kind of like shucking an oyster, or breaking open a Fabrege egg with a hammer and chisel.
You need Special Tool Number One (a hammer) and Special Tool Number Two (a steel punch, preferably a chisel-headed one; any width should work).
First you pull off the rear cog (the circlip comes off easily if you use a mini flat-blade screwdriver) and the dust cap. Then you need to remove the external components on the non-drive side; on the AW, these consist of the axle nut, washer, lock nut, lock washer and cone.
Now comes the fun part: knocking the internal mechanism free of the hub shell.
The internal mechanism is secured to the hub shell at the ball ring; the ball ring has two detents on its perimeter, probably designed to accept a special spanner which is nowhere to be found anywhere in the world, except perhaps in the shed of some old guy in Nottingham who used to work at the Sturmey-Archer factory, and took it with him when he retired. Or maybe it's in the bottom of the Lost and Found box down at the local pub. No matter; you don't need it. You can knock it free using the hammer and punch.
Put the wheel vertically across your feet, steadying it against your thighs with a forearm. Align one of the notches closest to your head and to your right (so, from the point of view of somebody standing in front of you and looking at you wondering what the hell you're doing, the notch is at their 10:00 position). Put the tip of the punch into the notch on the ball ring, and tap the punch so that the ball ring begins to loosen from the hub shell. Tap, tap, tap. You may need to reposition the notch to the 10:00 position a couple of times. Tap, tap, tap. Turn. Tap, tap, tap. (NOT thwack, thwack, thwack!)
It goes something like this:
The ball ring is made of of very hard steel, and will unscrew from the hub shell before the detent deforms. The angle here is kind of critical; you need to position the punch so that you get maximum purchase on the detent, but at an angle oblique enough to spin the ball ring. After a couple of taps you should be able to unscrew the ball ring/internal mechanism from the hub shell.
Once you take off the brake arm and the brake-side components, the internal mechanism can be removed...
...from the hub shell. (Note ridges machined on the inside of the hub shell; these are for one of the sets of gear pawls. Nice stuff.)
All the components in the top row (axle nut, washer, brake arm nut, brake arm, brake-side bearing assembly, and brake ring) must be removed before you can take out the internal mechanism from the other side of the hub shell.
Then the internal mechanism can be disassembled. A bench vise helps here.
There are all sorts of pretty little things inside a Sturmey hub (like, for example, the pinion assembly). What's amazing to me is that, even though they're based on the same principal (the epicyclic planet/pinion/ring), each hub model is so vastly different from the others. This was the first time I'd had a chance to pull apart an S3C. It wasn't too difficult, and I took the opportunity to clean it out a bit (other than being a little gummed up with varnish, it was in very good shape) but it took me a while to figure out what was wrong with it, and only after I tore it down, reassembled it, reinstalled it into the hub shell a few times. I had to peer at the leaflet a few times before it clicked.
It wasn't clicking.
For some really weird reason, the driver assembly's brake pawl springs (part HSA-459) were missing, so when you try to engage the brake, the pawls don't engage their ring and the brake shoe doesn't expand. A quick trip to Broadway got me a pair of $1.25 springs, and I was back in business.
The culprit: missing pawl springs in the driver assembly.
If I've said it once, I've said it a thousand times: thank God for Broadway Bicycle School.
Posted by smasher at July 12, 2003 09:39 PM