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Shimano Nexus and Alfine 8 Axle Unit Failure

Here are some pictures of a typical failure we see with Shimano Nexus and Alfine 8 speed hubs.

The tang on one side of the axle has a tendency to break off. Once this happens, it puts stress on the larger part of the axle which can crack and then stress the twin tang on the opposite side of the axle. The job of the tangs are to hold the main sun gear in place. The small holes you see are for a C-clip that keep the sun gear from moving sideways. We have seen this failure several times and is a strong example of why NOT to stand on the pedals on hills. The symptom you may have if this happens is the hub skipping gears. In the upper left photo you are viewing the main sun gear from the right (drive) side of the bicycle. This gear is being forced in a backwards (anti-clockwise, as viewed) rotation. In fact, all IGH axles are being rotated towards the back. This is why it is important to have non-turn washers that precisely engage the drop-out. A good mechanic will rotate the axle toward the back of the bike as s/he tightens the axle nuts to 32-35 foot-pounds.

It is our contention that modern internally geared hubs (IGH) (with the exception of NuVinci and Rohloff) cannot handle the forces created by standing or climbing super steep hills. The main reason for this recommendation is path dependency to the 3/8" (9.5-10mm) rear axle dimension. If IGH makers were to make a hub with a larger 14mm axle with flats that were 10mm wide (just like a BMX axle) then they could drastically increase the durability of the whole hub because the internal axle parts could be larger. The quest to save weight is another reason that limits durabilty. In our opinion, the benefits of IGH outweigh the slight increase in weight. Durability is the #1 reason people purchase an IGH.

The pictured axles are common to the Shimano 8 speed hubs including but not limited to: Alfine SG-S501 (axle unit # Y-35Z-98040), Nexus SG-8C20 (axle unit # Y-35P-98050) and Nexus SG-8R20 (axle unit # Y-34R-98040).