Nexus 8 still slipping

For discussions about bikes and equipment.
Brucey
Posts: 41359
Joined: 4 Jan 2012, 6:25pm

Re: Nexus 8 still slipping

Postby Brucey » 12 Apr 2020, 2:45pm

if there is still oil in there when you add the grease, it'll all mix up and become a runnier mixture. This will be fine provided it stays in the hub. Suck it and see I'm afraid.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

vandjq
Posts: 107
Joined: 16 May 2007, 11:30am

Re: Nexus 8 still slipping

Postby vandjq » 12 Apr 2020, 3:34pm

OK Thanks Brucey

vandjq
Posts: 107
Joined: 16 May 2007, 11:30am

Re: Nexus 8 still slipping

Postby vandjq » 19 Apr 2020, 12:41pm

Well I rode the bike for 40-50 miles before it slipped again in gears 1-4. This time I removed the innards and dipped them in ATF. Everything looked as good as new and the ATF has mixed well with the grease. Once again when I re-assembled the wheel the yellow marks lined up perfectly from 1-4 and 5-4. But after about 80 miles it slipped again in 2-4 and the yellow marks will not line up.

Now I know that the marks not lining up is usually a symptom of a sticking cable. But I have replaced the cable and housing four times and followed Brucey's advice on greasing the cable with Teflon/oil.

Given the excellent condition of the hub internals, I suspect that the fault lies outside the hub. This bike has vertical dropouts. The frame was replaced under warranty after the hub axle slipped and damaged the dropouts. Since then I have been tightening the axle nuts to 42nm as per the Shimano service manual.

In an earlier post Brucey mentioned possible problems with the axle:

The track nuts can back out, (even if they are tight enough to start with), if the NTW tangs are a slack fit in the dropouts, or the axle is a slack fit in the NTW. Either thing can cause the axle to turn (in alternate directions depending on whether you are using high or low gears) and this can cause the whole shooting match to work loose. If the frame is aluminium, it is possible for extensive damage to the frame to occur in this way.

[edit; if the track nuts are not 100% tight, the axle moves on one side (making the chain slack), and the frame is stiff enough, the axle can be slightly flexed out of shape, i.e. bent. This can inhibit the action of the gearshift within the hub, and make slippage in some gears likely. Usually when the wheel is remounted correctly, the axle goes back straight (i.e. it hasn't been permanently deformed) and the gears can mysteriously start working again.

If wheel slippage is persistent, one approach is to use some chain tugs to help prevent it. Batavus (amongst others) use some neat double-sided stainless steel chain tugs on their Nexus-equipped machines; these are not the strongest design, but they do have little cutouts in them for the NTW tangs; very many chain tugs simply won't work with Nexus hubs because they lack these features. The alternative would be a single-sided chain tug, but this would be thicker and have to go between the hub and the dropout; not all bikes will accept this.]


Now my chain is slack and my gears do mysteriously work again after remounting the wheel. I've had a look at those Batavus tugs on the Dutch bits website: https://www.dutchbikebits.com/batavus/b ... -tensioner

But I'm not sure which version to order or how the thing works. Any help would be much appreciated. I'm at my wit's end with this bike. :cry:

Brucey
Posts: 41359
Joined: 4 Jan 2012, 6:25pm

Re: Nexus 8 still slipping

Postby Brucey » 19 Apr 2020, 1:31pm

some photos of your dropouts might help?

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

vandjq
Posts: 107
Joined: 16 May 2007, 11:30am

Re: Nexus 8 still slipping

Postby vandjq » 19 Apr 2020, 3:08pm

Brucey - Photos attached as requested. Thanks for your help.

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vandjq
Posts: 107
Joined: 16 May 2007, 11:30am

Re: Nexus 8 still slipping

Postby vandjq » 19 Apr 2020, 4:51pm

Brucey - When I re-fitted the wheel I initially tightened the axle nuts by hand. The left hand nut was snug up to the cone locknut, but there was a 5mm gap on the right side. This meant I could see the frame moving as I tightened the nut with a beam wrench. I wonder whether there should be an extra spacer on that side? I've attached pictures of that as well.

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Brucey
Posts: 41359
Joined: 4 Jan 2012, 6:25pm

Re: Nexus 8 still slipping

Postby Brucey » 19 Apr 2020, 8:06pm

those are vertical dropouts and the usual way of fitting the NTWs is to fit the tang below the axle on both sides. In your pictures it looks like the tang is above on both sides, which might be right for this model for all I know but it looks like it hasn't always been like that and it certainly isn't usual. There is nothing to be gained from using chain tugs with vertical dropouts. The axle gap on the RHS is only about 2mm in the photo and it isn't unusual to see a gap of this size; Nexus 8 hubs are 135mm OLN as standard; there might be extra washers in some installations but this isn't usual.

The slots in the dropout need to be the correct width for the tang on the NTW. From the photos I would say this isn't the case, and furthermore if the torque load is taken on just one dropout, the dropout mightn't be strong enough.

I would suggest that you
- check that the tangs on the NTWs are the correct side of the axle
- verify and if necessary improve (eg by modifying and/or using shims perhaps) the fit of the NTW tangs

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

vandjq
Posts: 107
Joined: 16 May 2007, 11:30am

Re: Nexus 8 still slipping

Postby vandjq » 20 Apr 2020, 10:20am

Brucey - the bike was upside down when I took the photos, so the tangs are under the axle. Today I rode 18 miles without slipping, but when I got home I checked the yellow marks. Initially they were correct but as I repeated the test they started to go way out of alignment, then stuck completely going from 5-4. I have just turned the shifter down to 1 and the yellow mark is still stuck between 5 and 4.

Brucey
Posts: 41359
Joined: 4 Jan 2012, 6:25pm

Re: Nexus 8 still slipping

Postby Brucey » 20 Apr 2020, 11:03am

if the tangs are under the axle with the bike upside down (which was evident to me when I was looking at the photos) they are above it when the bike is upright. My comments relate to an upright bike, i.e. I think you have them the wrong way up. Your dropouts show marks from the wheel being in both positions at various times.

If the shifting is jammed between 5 and 4, try

a) releasing the axle nuts and trying again and/or
b) shifting quickly from 6 to 4.

if a) above works then it is indicative that the axle was somehow being strained when the axle nuts were tight. It would take a very stiff frame and/or a badly misaligned dropout to cause this with vertical dropouts.

As I have mentioned previously even with a new internal (with no cable connected) it is often possible to cause the shift mechanism to stall between 5 and 4 if you don't allow a 'run up' to this shift. A relatively small amount of axle flex, cable drag and/or adjustment error can turn this into a stall in use.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

vandjq
Posts: 107
Joined: 16 May 2007, 11:30am

Re: Nexus 8 still slipping

Postby vandjq » 20 Apr 2020, 12:01pm

Brucey - I should have said that the tangs are pointing to the open end of the dropout so are under the axle when the bike is upright. When I released the axle nuts that freed up the yellow marks. They were correct when I moved from 1-4 but way out when I moved from 5-4.

With the axle nuts still loose, I freed the cable from the cassette joint, then re-attached it. I am now able to line up the yellow marks perfectly in both directions. But when I tried to torque up the axle nuts the threads stripped.
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John w
Posts: 11
Joined: 27 Feb 2020, 10:05pm

Nexus 8 speed hub problem

Postby John w » 22 Nov 2020, 9:26pm

I've bought a new belt drive bike with a shimano nexus 8 speed with trigger shifter,
It slips/skips occasionally when in 4th gear.
Its really frustrating me.
I bought the bike online and as usual when trying to telephone the retailer they use covid as an excuse for not answering the phone.
I've lined the yellow marks and even tried the marks in slightly different positions.
Can this be rectified or is it a warranty claim??