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Intro

Just 2 months ago, I bought a new Cube Hyde Pro 2020 bicycle with belt drive (Gates, rear cassette out of metal, CDC with 22 teeth) Shimano Nexus 8 internal hub (model SG-C6001-8D). I mostly ride in the city and sometimes for fitness purposes.

Problem

Overall I am happy with the bike. It rides quiet and comfortable, but under high torque situations like short steep inclines or fast take-offs I have noticed a single sharp and unpleasant clunking noise from the gear hub. This happens in all the gears. I took a video of it on my daily commute on a short steep incline and gearbox in 1st gear.

What I tried

  1. First I made sure that the tension on the gear shifting cable was correct and that 2 yellow marks on the hub line up when the 4th gear is selected.

    Photo of rear belt drive hub

  2. Secondly, I checked the belt tension with the Gates frequency measurement app on the phone and it shows ~35HZ tension which is within the range recommended by the manufacturer.

  3. Third, I did some research, and it seems that few other users have noticed such behaviour even on this website. I actually found 2 threads with similar problem but with no clear solution:

I would greatly appreciate any help or input from you. Even if you don't have the solution but have observed the same behaviour, please reach out and maybe we can find the solution together.

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  • 1
    Two months, don't attempt any repair by yourself. The product is still under warranty. Take that bike back to the shop or arrange a return if you bought online.
    – Carel
    Oct 30, 2020 at 18:17
  • Whats the mileage? Alfine are recommended an oil change at 1000 km, and then every 5000 from then on. I suspect Nexus will be similar.
    – Criggie
    Oct 30, 2020 at 22:20
  • Thanks for the reply! Yes I will not try any major repairs, just the adjustments. If its serious I'll take it to the dealer. Mileage is low, 200 km tops Oct 30, 2020 at 22:25
  • This to be a common problem. I have the same bike from late 2018 and the same Nexus gear issue that has not been resolved by adjustment to the cable tensioning, and the realignment of the yellow marker. At £199+Vat for a new replacement gear with no guarantee of the same issue reoccurring when cycling mild/medium hills I really regret buying this cycle.
    – Steve
    Jul 30, 2022 at 12:21
  • The reliabilty of this Hub Gear is total and utter ****. Shimano pride themselves on reliablity. Having spent £190+ on a complete rear wheel rebuild with new rim and spokes (since the Shimano no longer sell 32" as per the spec for the 2018/2019 Cube Hyde Pro and the replacement hub now only fits 36") on top of £146 for the actual gear (knocked Tredz back by £50 on price match) its a total money pit. It was either that or dump the bike as the slippage of the gear meant the bike was at best unusable and at worst down right dangerous. Never again would I buy a bike from Tredz nor a Hub Gear from
    – Stephen
    May 17, 2023 at 15:42

2 Answers 2

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There are some Nexus and Alfine bikes that have made it out into the world with a spec mismatch between the over and under style cassette joints and the shifter.

The cable pull sequence works in reverse order between the two shifter types. Because the cable pull for this system varies with each click, everything gets screwed up if you then use the setup marks. Something like what you're experiencing can result.

To check this, get your exact cassette joint and shifter models and make sure they're listed as compatible on si.shimano.com.

If that checks out, test it with less belt tension.

If that's not it, get oil dunk gear and the Nexus/Alfine notchy tool, pull the core, wipe, inspect for anything out of place or prematurely damaged or worn, dunk, grease, reassemble, and see if that fixes it.

One perfectly likely explanation is that the pawls that drive the shell are having engagement problems. If one or more is under-lubricated, deformed, or out of place, it could cause a partial engagement problem, which also fits the symptoms. This can lead to a situation where the tips of the pawl(s) get damaged and the problem gets worse. This is easy to inspect for once the core is removed. Note that despite the ostensible complexity of the hub, the pawl system in question is the most exposed part of the whole deal, being the interface between the drive ring inside the hub shell and everything else. If it does the same behavior with the cable disconnected completely, I think this pretty likely is what's happening.

It is true that everything about this should be covered under warranty. Between parts shortages and the usual awkwardness of getting warrant support to happen for mail order bikes, it may get hairy at the moment.

Also check dropout alignment slash sync up slider fore/aft if applicable, all of which can in theory cause hub badness.

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    thanks for your input! I checked the compatibility and the shifter is compatible. I tried adjusting the cable tension away from the yellow mark. And by away I mean 0.5-1 turn of the adjuster. Also I decreased the belt tension to ~25-30hz and so far so good! I can take the same slope without the loud bang, and shifting feels a bit smoother. I will continue observing it's behaviour and still try to avoid applying to much torque to the system. Its crazy how sensitive these hubs can be and also how mark can be a bit off and misleading. Thanks for suggestions! Nov 2, 2020 at 0:05
  • Glad it worked. It's somewhat of a known issue that the published tension specs for Gates can be punishing to Shimano IGH hubs. Nov 2, 2020 at 0:08
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    @user2523745 would you be so kind to write your solution in an answer yourself? I don't think your method is included in Nathan's answer yet.
    – gschenk
    Nov 2, 2020 at 0:50
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After several suggestions and trials I think I have resolved the issue.

I tried adjusting the cable tension away from the yellow linup mark. And by away I mean 0.5-1 turn of the adjuster. Also I decreased the belt tension to ~25-30hz which is a bit below the recommended 35-50hz range and so far so good! I can take the same slope without the loud bang, and shifting feels a bit smoother.

I will continue observing it's behaviour and still try to avoid applying to much torque to the system. Its crazy how sensitive these hubs can be and also how the yellow mark can be a bit off and misleading.

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  • Great work! I found mine had to be backed off a couple turns from the "right" position, but that was on a bike with suspension, so sitting on it re-tensioned things. Very curious that yours wanted to go the other way.
    – Criggie
    Nov 2, 2020 at 23:26
  • how do we measure a tension in Hz?
    – njzk2
    May 23, 2023 at 17:50
  • @user2523745 Its been a couple years now, how did this solution work out for you in the longer term ?
    – Criggie
    Mar 28 at 21:10

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