Monday, 27 September 2010

Hopper hubs (pt 4)

This is the hub that is going be laced into the rear wheel for the Hopper. It’s a Steelite SAB 3 speed Sturmey Archer with a 70mm drum brake from 1994. I got it for £8 posted. Why so cheap?, well it’s because the axle has snapped in two.  The rest of the components are fine (missing a few ball bearings though), so with a new axle fitted it should be a fully working 3 speed braked hub for roughly half the price that a fully working one would cost second hand off ebay and about a quarter of the price of a new SAB hub. Plus, in the process I get to have fun stripping it down and fixing it.

This is a greased hub rather than an oil lubricated hub. Apart from the changes related to lubrication (i.e. sealing/ball races) the most obvious difference between this hub and the AW that came fitted to the Hopper is the width of the 3 speed internal mechanism. With this hub the internals have been shrunk down a bit to accommodate the width of the drum brake without making the hub shell too wide.

The trickiest bit of opening up these hubs can be unscrewing the Ball Ring. This needs either a special Sturmey Archer 'C' Spanner or a hammer and punch to get it loosened up. Normally it should be fairly easy to undo with a couple of taps, but this one was very stuck. Probably a side effect of this being a powder coated hub. It took some serious welly from a hammer and chisel to get it free. I ziptied the brake to keep it locked in the hub so that I wouldn't damage the thin lip near the spoke flange when it was in the vice.

You can see from this photo that the hub shell is wider.

Whilst in this photo you can see the internals are more compact. These two aspects together provide the room for the drum brake.

These hubs are very easy to strip down and shouldn’t be intimidating to anyone who fancies having a go. I would do a write up of stripping a standard AW hub, but there is no point when I can just direct you to this youtube video which covers almost everything.

One thing to remember when playing with these hubs though is the pawl springs. They are tiny. If you aren’t careful you could tip up part of the internals, a pawl pin can drop out and the pawl spring will vanish from the face of the earth. So it’s a good idea to put an elastic band around the pawls whilst you are working, just in case.

Here’s the disassembled hub. You could strip it down more than this, right down to every single individual part but this is enough for me to get it fixed and re-greased.

The original axle is a HSA534. You can't buy these, so you could be forgiven for thinking this hub is not repairable. But the reason you can't buy them is they have been superceded by a better design. This better axle is the HSA571, which is available quite easily. On the old axle the Sun Pinion is a seperately machined piece which has been stamped permanently onto the axle - this creates an inherent weak point and is the reason this axle has somehow gotten snapped. The newer HSA571 axle is machined from a single piece, problem solved. In this photo I've removed the small circlip from the old axle, ready to put it on the new one - it holds the Planet Cage assembly in place.

I couldn't find out what grease you are supposed to use in these hubs, or anywhere obvious which sold the actual Sturmey Archer grease. So I got a tube of Shimano internal hub gear grease. If it works in more complicated 7/8 speed Nexus hubs then I figure it will work ok in a simple 3 speed. the hub was making all the right noises when it was greased and back together, so it should be fine.

Here is the hub all cleaned up and rebuilt with brand new outer parts such as wheel nuts, indicator chain, brake cable parts and brake arm clip. It's now all ready for lacing into a wheel and testing out. The front wheel will get a standard X-FD drum brake. Happy days :)

You can find the Technical spec in PDF form on Tony Hadland's excellent site, which is essential for finding out the parts numbers. As with all these things though, you can only learn so much by looking at the exploded diagram, best to take it to bits and find out for yourself.

1 comment:

  1. I've just downloaded iStripper, and now I enjoy having the hottest virtual strippers on my taskbar.