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Inside the Sunrace-Sturmey 8-speed

As some of you may already have read over in the VV Forum and as hinted at in VV18, the third of the Sturmey-Archer 8-speed hubs I've tried broke recently.

I know a number of readers have been following the ongoing reports in the magazine about my experiences with the Sturmey-Archer 8-speed hub with interest. It seems I was sent a number of hubs which weren't really fully-developed - and I've broken three so far. But fingers crossed, it looks like they might have cracked it now...

The good news is that the new one they sent, which I built into a wheel for my town bike and have been using for a few weeks now, is MUCH better. Shifting is far more precise than ever before, it's still lovely and silent, and feels pretty efficient too. I've also heard similar very positive reports from Tony Hadland who also has a latest-generation Sturmey 8-speed. Apparently someone who tried his, a Rohloff user usually, compared the Sturmey's shifting favourably...

If the hub is now mature, many people are holding out hope that it'll be squeezed into a Brompton rear triangle before long... finally giving that bike a decent range of gears at a feasible price.

Anyway, in the meantime I thought I'd have a go at taking one of the old ones apart - Sturmey didn't want it back, as it failed from a cause already known by then. I don't think they should mind me showing detailed pics of the innards - any competitor wanting to copy the hub will simply have bought one. But realistically, there's such a tooling cost involved anyway that this is pretty unlikely.

Please note this is not an 'official' guide about how to do it. No doubt, expecially when reassembling, there are alignments to be observed and torque settings to be adhered to. It's for interest only.

We'll start with the hub, with sprocket and axle nuts removed:



First stage is to remove the circlip:



This releases the shifter cable support plate and a washer:



This exposes the drum which the gearchange cable wraps around and rotates to change gear. Remove the nut, and this and a few spacers are released:



Another plate is exposed:



This just pulls off, revealing the first set of bearings.



The hub had been used hard for six months or more, but the bearing races look like new:



Pull off another plate and you can see the spring which tensions the gear change cable. Note also the still-clean grease on the ball race.



These parts also just pull off now. The ballrace is secured behind a press-fitted sealing ring, so I couldn't remove it. There was also a thin cylinder-ring type seal in a groove around the outside, seen below the part.



Inboard of this ring is another bearing surface, again gleaming as new.



Next pop off a plastic shield and you can unscrew (left-hand thread) the large-diameter outer race. This screws into the hub with a fine thread. You really need a large pin spanner to remove this, or a special tool. Again, bearing surfaces pristine:



At this point the hub innards are ready to come out:



But first you need to flip the hub round and release the hub brake parts:



Just undo a few nuts and it all pulls off:



Just the cone left:



and you can pull the innards out leaving the hub shell:



Inside there's a freewheel ratchet ring and axle bearings, again with clean grease:



The innards are one solid lump:



And a reverse view:



The reason for the hub's failure is now revealed, too:



The ring gear has burst in two places:



Removing the circlip from the end allows the damaged part to be removed:



A number of gear fragments fell out at this point. One of the planet gears was missing, with just the pin remaining.



Leaving that for now, we can continue to disassemble: the various stages of the transmission simply pull off the axle:



The largest stage, all greasy. The grease was mostly pretty clean still.



Each stage has three freewheel pawls on its outside, which engage with a ratchet ring at the back of the previous stage.



Looking at the axle with some stages removed, we start to get an idea of how the shifting works:



There are three wee spring-loaded shifter levers, recessed into the axle, and controlled by the three rings on the other end. When raised, the levers engage with the splined bore of the planet gears rather like the pawl of a freewheel:



Removing a circlip lets the controller rings slide off. These have a cam-like profile, which clearly controls the shifting sequence:



The shifter levers can now drop out:



And all three posing for the camera:



At this point it's about as disassembled as I can go. The 'stages' seem to be press-fitted together from two main parts, holding the 'sun' and 'planet' gears within. So after a little cleaning just time for an exploded pic:



Click here for a full-size (3000 pixels wide, 300k) version


Another pic of some of the gears:



And now I'll put it back together, just to prove I can :-)

As this is a non-working hub I've not regreased before reassembly.

First get all those wee springs and shifter levers back in place, slide on the controller rings (they're coded A B and C), slide all the controller rings back onto the axle, and secure with the circlip.

Reassemble the pawls and spings onto the gear units. Then slide the gear units back on:



Don't forget this shield thingy which goes on before the first gear set:



Fit the final freewheel pawls and replace the circlip and the innards unit is now complete:



Refit the axle bearing cone:



and replace remaining drum brake parts:



Now flip the hub back over, and screw the big bearing ring into the hub shell:



Add the bearing race, and settle the next bit in place:



The bit with the two 'prongs' sticking up engages with the 'controller rings' which handle gear shifting:



Those prongs engage through to the cable drum, now fitted along with the plastic shield for the outer bearing race:



Just a few spacers to go:



Add the shift cable support plate, washer and circlip:



and it's done!

Posted on 22 June 2005