Nexus Hub Blues

[WalthamCity]

I ride a Nexus 8 internal hub gear. The bike is about 6 months old. Initially the hub gear was great, smooth and quick changes up and down. Recently, however, it has been performing quite badly.

* When I change in low gears, the shifting is sometimes slow, and often make a loud metal "crack" as the gear engages.
* When I change in high gears, sometimes the gear slips "into neutral" - i.e. I lose all power. This is fixed by changing up and down the gears. It seems to happen most frequently when shifting from 6 to 7 at speed.

* The yellow cable tension marks are perfectly aligned, but I have noticed that even a tiny misalignment causes gears not to shift at all. When new the hub was much more forgiving of a small misalignment of the yellow marks.

Since the hub is a "black box" these problems are very hard to diagnose, and I'd appreciate advice on how to fix them.

Could it be that the hub just needs its annual bath in expensive Shimano hub oil? Or is there something more seriously wrong? (The bike is still under warrantee). Is this just normal performance for a Nexus 8 and I just need to live with it?

I'd appreciate thoughts your thoughts. The bike has been serviced recently and I was assured that there is nothing wrong with the gear-change cable.

[Brucey]

if the bike is under warranty, take it back and have them fix/replace the hub under warranty. I do not think it is acceptable for a hub of that sort to fail at that age/mileage i.e. before the first service is due. Do it now, don't wait; that is 'a product that is unfit for the intended use' if it fails that soon.

If the hub were out of warranty then that is a different situation, but shimano products carry a two-year warranty against manufacturing defects.

FWIW if I had a new Nexus hub I'd use a different lube in it from new even if it meant 'no warranty' simply because in the UK weather there is still a pretty fair chance that the hub will get water in it if you stick with the shimano lube scheme.

Your hub failure may or may not be related to water ingress/lube failure, but it shouldn't fail that soon and it shouldn't really be your problem if it does.

cheers

[WalthamCity]

Interesting. So the described behaviour is a failure of the Hub? That's all I needed to know. I'll head to the shop I bought it!

[gregoryoftours]

Just to make sure, when the yellow lines hit bang on it should be in 4th gear for Nexus 8sp.

[NATURAL ANKLING]

Hi,
So do Shimano get feedback / do they allow even direct from customers

[gerrymcm]

I had an issue with an N8 and the simple process of disconnecting teh shifter cable, re-lubing it and the shifter and then refitting it all resolved a seemingly very serious shifting issue. when I refitted it all the yellow dots didn't line up whereas they did before leading me to think that the cable in the housing or the shifter wasn't moving properly/fully and was therefore not allowing the rotating "cassette joint" to change the gears correctly.

good luck, they're great hubs provided the H20 penetrate!

[WalthamCity]

Yes - the yellow marks are bang on in 4th. The frustrating thing trying to diagnose issues is, as a complexity sealed unit, you can't see what it's doing or why gears aren't engaging.

[Brucey]

Yes - the yellow marks are bang on in 4th. The frustrating thing trying to diagnose issues is, as a complexity sealed unit, you can't see what it's doing or why gears aren't engaging.

well if you could easily see the workings, they would get dirty, which is why they are not on show.

If you do take one of these things apart they are in fact not that complicated. My point is that when the bike is new and under warranty, you shouldn't need to be doing that.

The gear is a 2x4 gear internally. The 2s gear has a direct drive or a reduction option. The 4s gear has a direct drive and three increase options. Thus gear 5 is direct drive and 6,7,8 use the 4s gear to increase that. Gears 1-4 are the same as 5-8 but the 2s gear is used in its reduction mode.

FWIW inside there are only four parts that move when different gears are selected, and you can see those moving in the right way (or not) once the centre is part-disassembled. The amount of disassembly required is slight; the centre comes out once the cone and locknut are removed on the LH side, and to gain access to the moving parts of the shift control, it is only necessary to remove one circlip which then allows the planet cage assembly to slide off the axle.

Please note that under normal circumstances there are only two types of 'slippage'; slippage of one sun (which should leave you with drive in the next lowest gear) , or slippage of the two-speed clutch, which is usually engaged when shifting from 4 to 5, and should remain engaged in all higher gears.

Thus if the hub exhibits gross slippage in (say) 6 or 7 it should never slip to 'no drive at all'; it would normally slip to the next lowest gear (if a sun fault) or slip to a gear that is four lower, ( i.e. 7 would slip and give you gear 3) if the two-speed clutch slips. The latter may feel like no gear at all, because the gear you might get is only a little over half the size of the one you wanted.

If the 2s clutch slips in gear 7 this means there is a catastrophic fault with the external gear shifting control (which ought to be obvious from the outside) or there is an internal fault of some kind with the 2s clutch.

BTW if you believe what some people will try and tell you, you may have been shifting this hub under full load. This is never a good idea; you can make most shifts under a modest load but if you shift 4-5 under heavy load the 2s clutch can be damaged. If the hub is ridden with a sticky cable or a maladjusted cable the shifts won't be in the right place and the consequent slippage will damage the hub.

If you try and make some shifts under full load (or even when stopped with your foot on the pedal) this will either work (or overwork) the shift control spring inside the hub (which only has limited travel) or it will allow the gear cable to go slack and the housing to pop out at one end; if it does this and then doesn't go back in again, all the gear adjustments thereafter will be out of kelter.

With the exception of the 4-5 shift, most of the shifts in this hub should be 'slicker than a slick thing'; all you need to is to carry on pedalling forwards (but without any real load) for a fraction of a second and the gear should go in very smoothly. Most people take brief instruction and then a test ride before they buy, so they know how the shifts should feel.

It therefore worries me that you think that clunking of any kind might be 'normal'. This implies that

a) you perhaps didn't get instruction or a test ride prior to purchase and/or
b) you may have been riding the bike for a little while with an ongoing fault;

the latter of which is extremely unlikely to improve matters. IME if the hub slips or makes a noise there is almost invariably something wrong with it or the way you are using it. If the cause is identified and rectified immediately a small fault can be prevented from becoming a large one; however if the hub is ridden on and highly loaded whilst it might for some reason slip, then a hub with a small adjustment fault (say) can soon be smashed to pieces inside.

cheers

[WalthamCity]

Thanks for all the advice on this thread.

To give you the (I hope) the end to the story I took the bike into the shop where I bought it. They initially thought that the hub needed to be sent back to Shimano under warranty, but had a thorough look and came to the conclusion that the cable was at fault. They've replaced the cable and it seems to have fixed the problems. For now, at least, the hub gear is back to its smooth-shifting reliable self.

If it plays up again they will send the hub in for warranty service.

[WalthamCity]

On the "clunking might be normal". All bike parts degrade over time, and there are very clear visual signs when, eg a brake is worn down or if a chain is failing. What isn't clear to me (and still isn't!) is how a hub gear "ages" and tells you it needs a service and Shimano oil bath. I thought clunking might be a sign of this. If it isn't, what is?

[Brucey]

what IGHs (along with a load of other bike parts) really need is preventative maintenance. If you wait for funny noises to appear then that is usually too late; the hub is already damaged or being damaged. [By analogy you can't tell when your car needs a service; you just know (by time or mileage, or a little light that comes on which might work the same way...) that it is due; if the car is already behaving weirdly, the chances are excellent that something is broken and it is a repair you need, not just routine servicing].

If the shifter is not controlling the cassette joint on the hub correctly, you will be riding around (full load) with the hub set 'between gears' ; a good analogy for this is to try and change gear in a car without using the clutch, whilst your foot is flat to the floor. You wouldn't expect a car gearbox to last long like that and it would definitely make funny noises whilst you were trying.

In your original post you mentioned that 'the marks were lined up correctly' and yet in the end it turned out that the cable was bad. I may be labouring the obvious here but it is not sufficient for the 'marks to be lined up correctly' some of the time, they have to be lined up correctly all of the time i.e. whenever and however fourth gear is selected. It is almost invariably the case that if the cable is bad, the marks line up differently in fourth gear depending on whether you upshift to fourth or downshift to fourth.

In hindsight slow or delayed shifting can be symptomatic of a bad cable too; however if the shift to fourth were delayed or didn't happen, this ought to have been obvious, since the marks would not have been lined up correctly at that time.

BTW I have mentioned this before elsewhere but sticky cables/cassette joints are the #1 problem with these hubs, and accurate diagnosis is not that easy; once in a blue moon the cable will move freely for part of its travel and if that happens to be near fourth gear, everything can look wonderful because the marks line up in fourth gear OK, even though the shifting may be all to cock elsewhere. There are already similar fourth gear alignment marks on the underside of the cassette joint (NB that you can always wipe clean, unlike the upper marks that often get dirty behind their 'window'). I think it would be an excellent idea to have a mark for each and every gear instead of just fourth gear; that way it would be much easier to diagnose sticky cables, however and wherever they are sticky.

Note also that I have encountered a few people who just don't (or won't) shift these gears in the right way. They routinely (regardless of what they are told, or how many times they have already had problems) try to downshift under full load, which (on most N8 gears) sends the cable full slack. Once that happens, all bets are off; the cable can come unseated at either end or come out of the groove in the cassette joint; subsequent to this, the least likely thing is that the hub will then behave normally.

So my advice is
- always shift the gears without load; carry on pedalling forwards as you shift, but without load on the pedals.
- get in the habit of checking the gear alignment in fourth, confirming that the alignment is perfect (and prompt) on both upshifts and downshifts to fourth gear.
- service the hub regularly if you want it to last.

cheers

[NATURAL ANKLING]

Hi,
On a motor cycle its possible to shift quite smoothly with out the clutch.
I always used the clutch, some style of riders could probably get away with clutchless changes and if it not your pocket they probably do.
You can and do get horrible noises on motor cycle gearboxes when you slip or drop a gear, not using the clutch would accelerate the dogs rounding off and then you would need to hold the gear lever to stop it dropping out.
You meet riders sometimes out and about and non jokingly openly say they don't use the clutch on trail motorcycles but like I said its probably often not there own pocket that pays, funny how people are sometimes.
I am not au fait with modern one day trials machines and they might well have a clutchless change box, would make sense maybe, just like the abs and non slip non wheelie software they use on pro race motorcycles, I was quite surprised at that, they probably have auto clutch like F1 too.

I am no saying that the OP abuses the box in anyway, its fixed, but watching riders sometimes is a real eye opener.

Old story - my mate rode a Yamaha 50 auto step thru, he said it would never wheelie......yes it will..so me and my other mate picked up the rear of bike by the luggage rack the rider gave it full bore in first and we dropped the rear.......its wheelies ok

[gregoryoftours]

So my advice is
- always shift the gears without load; carry on pedalling forwards as you shift, but without load on the pedals.
cheers

I knew that you weren't supposed to shift under load, but wasn't sure about pedaling without load - is this the preferable way of shifting or is it equally ok to stop pedaling entirely or even back pedal a touch if at a standstill? Are all 1 cable hub gears the same in this regard, eg nexus, alfine, old sturmey archer 3 speeds etc?

[Brucey]

quite a few hubs won't shift every gear completely (or some gears at all) if you change whilst stationary, whilst not pedalling, whilst pedalling backwards. The reasons for this can be both complex and varied. Even some of those gears that will seem to shift when stationary often are then 'doing something' - that could result in damage to the hub- when you start pedalling forwards again following a stationary shift. [ Possibly the worst kind of stationary shift in some hubs is one where you have your foot resting on the pedal when you work the shifter; this is just the kind of shift that some folk want to do when stopped at the traffic lights.]

It is also rare that all the shifts in any one hub work the same way. For example shifts 1-4 and 5-8 (in either direction) in a nexus 8 hub will 'go' reasonably well when stationary; 4 to 5 is not so good, but 5 to 4 is better.

So if you want a shifting technique that works with any hub, any shift, it is to shift whilst pedalling forwards without load; they all work OK like that, and perhaps importantly you can feel when the shift has gone in and you ought to know when it is OK to pedal hard again.

For other shifts it is a question of becoming familiar with any one hub's characteristics. You can usually work out if certain shifts are going to be OK or not under various circumstances, if you understand the way the hub operates internally. Past that, you need to do your own experiments or seek guidance from others. Experiments can be a bit iffy; if you don't feel through your feet what is going on, you can think things are wonderful when in fact they might damage the hub.

cheers

[gregoryoftours]

Thanks for that answer, it's very interesting, I've always thought that ideally you were supposed to shift without pedalling so it's good to know the right way.