More Nexus 8 gear problems

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fenmanctc
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Joined: 15 Dec 2013, 10:10am

More Nexus 8 gear problems

Postby fenmanctc » 6 Jan 2021, 8:19am

Suggestion welcome. I have an e- bike fitted with Shimano Nexus SG -C6000-8R hub gears. This has covered 3,850 miles of gentle use on flat roads. Gears 6,7 and 8 are slipping intermittently. It seems worst in 7th. The strange thing is, they don’t slip while changing DOWN, only when going up, when the cable is under increasing tension. Most odd! I have changed the inner cable, made sure the pinch bolt is tight ( awful design IMHO) and precisely indexed things by lining up the yellow dots in 4th.
Any ideas ? I have a smooth running Alfine hub on another bike, but I’ll bet the innards aren’t transferable. Can’t swap the hubs as one is 36 h, the other 32..........Ah, well , looks as if I’m going to have plenty of time at home to fix it!

Brucey
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Re: More Nexus 8 gear problems

Postby Brucey » 6 Jan 2021, 10:00am

slipping following gear changes in one direction only suggests that the cable/CJ (cassette joint) isn't perfect and that the gear selection position varies depending on whether you upshift or downshift to any one gear.

One of the pernicious ways this can happen is if the cassette joint arm isn't always free to rotate ACW [edit; I meant CW of course....] until it hits its stop. If it isn't, (eg because the cable housing pulls at it, and/or the NTWs are allowing the axle to turn, which will have much the same effect) then gear selection will be hit and miss. The latter fault won't appear on the workstand, only when you are actually riding the bike.

So if the tangs on your NTWs are a sloppy fit in the dropouts, or the NTWs are worn against the axle flats, and/ or the track nuts are not tight, and the cable housing is interfering with the position of the CJ arm, the installation is bad and you should expect problems of the sort you are seeing.

A final comment is that often lining up the yellow marks exactly isn't the best setting for the hub anyway. Up to 1mm more cable pull (i.e. so the yellow marks are staggered) may make gear selection more reliable, not less.

cheers
Last edited by Graham on 6 Jan 2021, 12:57pm, edited 2 times in total.
Reason: strikethrough added using [s]target[/s]
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fenmanctc
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Joined: 15 Dec 2013, 10:10am

Re: More Nexus 8 gear problems

Postby fenmanctc » 6 Jan 2021, 11:45am

Thanks for that, Brucey. I’ll try the simplest first, that is to adjust the cable a notch or two. Can you tell me what ACW stands for? I’ll try to look at the cassette joint next and work through the other suggestions. The gear changer is a twist grip. Can they get worn? Is this likely after < 4000 miles? I have an Alfine trigger shift to substitute if all else fails.
Cheers

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mjr
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Re: More Nexus 8 gear problems

Postby mjr » 6 Jan 2021, 12:07pm

fenmanctc wrote:Thanks for that, Brucey. I’ll try the simplest first, that is to adjust the cable a notch or two. Can you tell me what ACW stands for?

Anti Clock Wise
MJR, mostly pedalling 3-speed roadsters. KL+West Norfolk BUG incl social easy rides http://www.klwnbug.co.uk
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Brucey
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Re: More Nexus 8 gear problems

Postby Brucey » 6 Jan 2021, 12:25pm

yes that is correct, but I am a twit, I should have said CW of course, for the cassette joint arm on a Nexus 8...d'oh!... :oops:

I shall revise my post accordingly.

cheers
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simonineaston
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Re: More Nexus 8 gear problems

Postby simonineaston » 6 Jan 2021, 1:02pm

A final comment is that often lining up the yellow marks exactly isn't the best setting for the hub anyway. Up to 1mm more cable pull (i.e. so the yellow marks are staggered) may make gear selection more reliable, not less.
Are we taking a millimetre between the centre of each yellow mark as a rough indication of a millimetre of cable pull? (The former being a short arc of a circle, the latter being the actual cable pull...) Or am I worrying unduley?
EDIT: I think the answer to the last Q. is "Yes".
byyeee,
SiE