Nexus 8 Gear 5-4 Shifting Problem

[fstopman]

I am running a Nexus SG-C6011-8V, which is a low-normal hub with roller clutches. I think it's the same internally as the 6000-series Alfine 8.
Occasionally, after downshifting from 5 to 4, I hear and feel a loud pop. This may happen a couple of seconds after the shift seems to have been completed. I would guess that it happens only once in every 20 or so shifts from 5 to 4. This has been occurring since the hub was new (5 months). I've probably ridden only a few hundred miles on it.

Shifting technique: Pedaling with light effort;
Axle Nuts: Tight;
Dropouts: Short horizontal (Bob Jackson World Tour frame); no obvious misalignment. Nominal spacing of 130mm (hub OLD is 132mm).
Alignment of yellow marks on cassette joint: Very good whether shifting from 3-4 or 5-4;
Cable: Shimano with recommended ferrules, continuous housing from shifter to cassette joint; no apparent "hanging up".
Shifter: Microshift bar end for Nexus 8 (with friction adjustment per Microshift instructions).

I am careful not to shift under load, I've replaced the inner cable, and I check the yellow alignment marks obsessively. I'm now trying to "mis-adjust" the alignment a bit to see if that helps, but so far, no luck.

Do any of you have any experience with this issue?

[Brucey]

in gear 5 the sliding clutch is engaged, and the drive is taken from the driver to the secondary planet cage, and thence to the hubshell via the roller clutch at the far left of the gear.

In gear 4 the sliding clutch is disengaged, there is a roller clutch that drives from the primary ring gear to the secondary planet cage , the gear 4 sun pinion is locked to the axle by a single pawl, and the drive is taken by the secondary ring gear to the hubshell by another roller clutch.

Gears 2 and 3 work the same way as gear 4 except there is a different sun pinion locked to the axle.

A noise in gear 4 may be caused by

- the primary sun pinion moving on the axle
- the roller clutch between the primary and secondary gear taking up load
- the roller clutch on the secondary ring gear that drives the hubshell taking up load
- the gear 4 sun pinion not locking perfectly and slipping round one tooth
- the roller clutch on the secondary planet cage (that drives in gear 5) disengaging.

Some of these ought to happen after you freewheel in gear 4 or when you shift from gear 1 to gear 2, or gear 3 to gear 4, or gear 5 to gear 3, that kind of thing. So try a few other shifts out and see if any of those produce the same symptoms or not.

That it doesn't happen every time suggests that it is the gear 4 sun locking which is a bit quirky.

cheers

[fstopman]

Brucey - Thanks for the infos!

Normally there is no noise in any gear. The "pop" I sometimes get is only shortly after shifting the lever from 5-4, as soon as I exert some pressure on the pedals.

What I just noticed on a ride today is that if I exert "some" pressure on the pedals whilst shifting, I feel and hear the hub "clunk" into gear 4. This seems to work every time. If I shift while stationary, or turning the pedals with no pressure at all, occasionally the shift seems not to be completed until I exert some pressure again, whence I get the "pop" sound and the shift is completed.

For now, I guess I will just try to exert a little pressure when I shift 5-4...

[Cyril Haearn]

I thought my hub gear was very quiet but I went for a ride in the country, heard it ticking quietly, in town I cannae hear it

With a hub gear we were told to stop pedalling when changing gear, I usually keep turning the pedals without stopping but sometimes the gear does not change, should one stop turning the pedals for a moment?

[Brucey]

...With a hub gear we were told to stop pedalling when changing gear, I usually keep turning the pedals without stopping but sometimes the gear does not change, should one stop turning the pedals for a moment?

depends on the gear; the most reliable shift technique is to continue to pedal forwards but without any pressure.

cheers

[Stradageek]

I'm intrigued now Brucey, for all the three speed hubs I've used (Shimano and SA) I've always used a very quick 'pedal pause/slight back pedal' technique which seems to ensure a rapid positive shift with minimal delay/loss of speed.

Is this peculiar to the hubs I've used and will it work on my newly acquired Sachs 3x7 (BikeE recumbent)?

Cheers

Stradageek

[Brucey]

there are all kinds of things that will work but some are better than others. I suspect the advice to freewheel or backpedal was originally given to owners of 3s hubs simply because it wouldn't break the hubs. It isn't as quick and efficient as forward pedalling, no load (lets call it FPNL) shifting. Some hubs (eg some SA 5s ones) won't do some shifts at all when freewheeling or pedalling backwards, indeed the shift is delayed until you pedal forwards and there are extra springs in the hub that are there to ensure that this happens. If you pedal forwards hard, you can damage the hub as the gear goes in.

I would go as far as to say that that with even a modern NIG AW, the practice of shifting whilst not pedalling is pointless at best (this shift may not go in, in some cases) and it is positively harmful to shift whilst backpedalling; this just wears the actuator plate faster than normal.

cheers

[Cyril Haearn]

Got a back-pedal brake, cannae pedal backwards

[Cyril Haearn]

What about Rohloff, when changing 8-7 or 7-8?

[mchillingworth]

Can anyone recommend a good mechanic/shop for Shimano hub gears? I have the Alfine 11 that is playing up.

[Brucey]

Can anyone recommend a good mechanic/shop for Shimano hub gears? I have the Alfine 11 that is playing up.

location?

What about Rohloff, when changing 8-7 or 7-8?

it is pretty much the same deal as with a 5s hub; the shift needs to 'go in' before you stomp on the pedals again. You can feel this happening if you go FPNL.

cheers

[fstopman]

OP here, with an update on my Nexus 8 shifting observations:

1) Shifting 5-4 whilst pedaling lightly sometimes results in shifts that are incomplete; I can feel that the ratio has changed, but when I apply more pressure, there is sometimes a "pop". The crank doesn't "slip"; the hub just makes a noise. This only happens once, shortly after the shift.

2) Shifting 5-4 with "some" pressure, the gear changes and there is never, or almost never, a "pop" when I apply more force afterward.

3) Shifting 5-4 whilst not pedaling, that is, beginning and ending the shift while the pedals are not moving, seems to result in no "pop" at all.

My solution for the moment seems to be to make all shifts whilst the pedals are stationary. This has always worked, regardless of what shift I am making, even shifting several gears at once. Maybe later, after I do a dunk in the special magic Shimano oil, the hub will be less particular about my technique.

All this is a bit confusing. Shimano recommends to pedal lightly and shift only one gear at a time. People who know these hubs very well (Brucey, Aaron Goss) recommend shifting whilst pedaling lightly. Some users report that they are shifting while standing on the pedals - no problem! Others say their experience, and the recommendation from their LBS, is to stop pedaling whilst shifting. Quite a lot of divergence of opinion re. a component that is supposed to be simpler than a derailleur...

[Brucey]

most of the shifts can be done under some load but the 4-5, 5-4 shifts in an N8/A8 hub involves a sliding clutch. To expect this to fully engage under load is a big ask.

cheers

[Stradageek]

Thanks Brucey; seems like the answer is either to totally understand the internal workings of each hub or just try it and see what works best.

My son couldn't consistently engage 3rd on his old Shimano 3-speed until I suggested a fractional freewheel then fractional backpedal (FWBP) and my wife had trouble with her old SA AW3 until I suggested the same - but maybe this just translates into a period of light loaded forward pedaling as they start pedaling again.

So maybe with FWBP each gear change is getting a fraction of a second unloaded, back rotated and lightly loaded in sequence i.e. FWBPFPNL (the whole sequence takes less than a second) - and one of these will be correct.

Sorry about all the abbreviations

I'll experiment with my new Sachs 3x7.

As and addendum Brucey, can you tell me what the issue is with the no-false neutral SA 3-speed fitted to the Pashley postie bikes? I seem to recall something about destroying the hub by wheeling the bike backwards - or am I mis-remembering?

Thanks as always

Stradageek

[Brucey]

the NIG 3s hub (all current (2001-) toggle chain 3s hubs near enough, plus all 5s hubs from ~1992 onwards, and some export 3s hubs 1983-1999) has a thing called the actuator plate that (when the bike is wheeled backwards in top gear) prevents the hub from smashing itself to pieces. However

a) it isn't really strong enough to do the job, and
b) it sees a load every time you backpedal in some gears (eg during shifting) and it can fatigue.

without one fitted at all in top gear the clutch ought to pop out of engagement with the planet cage (if the bike is wheeled backwards), and (apparently, I have not tried it) it will do. However if the chain is loaded in any way as the bike is wheeled backwards (eg if a foot is on a pedal or the crank swings round against the back of a propstand, then the clutch is less likely to move and the gear can break itself, because there are parts that are trying to go at different speeds with no place to go. If it gets loaded up like that the actuator plate is meant to disengage the pawls on the driver. It normally does this Ok a few times and then it can break or fatigue.

If you never pedal backwards then the actuator plate never really sees any load, so doesn't get a chance to wear out or fatigue or break.

If you have a coaster brake hub of this type then the actuator plate sees load every time the brake is used and every time you freewheel.

The part is not expensive and can be changed in a few minutes. Not a bad idea to change it once every few years anyway.

cheers