BrownhillsBob's #365daysofbiking

On a bike, riding somewhere. Every day, rain or shine.

#365daysofbiking Gearing up

January 3rd – One of my bikes uses a Shimano Di2 hub gear – an Alfine 705. This is the original Di2 11 speed hub and has its own pros and cons, but on the whole it’s reliable and workmanlike, and apart from a somewhat fiddly oil change when the shifting gets lumpy, requires little in the way of mechanical attention during it’s lifetime.

Generally, the life I’ve found is about 15-25,000 miles. This hub has been through a lot, and more than 3 wheel builds, but I’m happy with the wheel it’s in now, which was why it was so annoying when it suffered a serious failure on Christmas Day. I lost about half the gears which just spun out when selected – 3,4,5, 9 and 11 I think. An oil change and filling with cleaning oil hadn’t helped at all. The hub was knackered.

There’s not much I don’t know about this system; I’ve been using it in different iterations for over a decade and I’ve got to know the tricks and fiddles and advanced maintenance procedures – both by reading manufacturer documentation and by trial and error. The internal mechanism of the hub is easy to remove and change for another – you remove the wheel, take off the changer mechanism, sprocket and disk brake. You then remove the non drive side cone and locknut, then unscrew the plastic retainer and oil seal on the drive side – I have the right tool for this but a strap wrench will do it fine too, but the key bit is it’s a left hand thread. Once it’s off, the whole gubbins will come out, the oil can be cleaned out and a new mechanism can be put back, or the old one repaired and refitted.

There was a snag. The 705 is no longer available, but there is a new version, the 7051. I didn’t want to rebuild the wheel. I scoured fleabay and the web for a 705. No dice. I found a brand new 7051 in Germany for about £250, which is a great price. I poured over Shimano drawings of the two hubs. I decided to risk ordering the 7051 and trying to swap the innards. If they didn’t fit I could always reassemble it and build a new wheel.

In time the hub arrived, and the good news is it fitted exactly the same. On the rare chance that anyone ever reads this wondering if it’s possible to swap the two, yes it is. I swapped the guts, but also the non drive side bearing and oil seal too – be careful popping that out as they’re easy to damage and if no longer flat, oil will leak from the cone.

The 7051 hub has an upgraded clutch, smother shifting and performs better changing under loading. I have to say, fitting it back was a dream, and it runs well. Once the factory stiffness had gone, changes are much smoother and there’s far less clatter when doing so.

The old hub mechanism I plan to dismantle to see what’s gone. Looks like I’ll be spending some time in the garage with the tools…

This post has been created on the off change anyone ever wonders the same thing: I would say this also applies to the non-Di2 cable variants too.

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One Response to “#365daysofbiking Gearing up”

  1. 480638

    Fascinating article. similar principle to an auto gearbox in a car, in miniature.



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