I am working on a bike at the recycling project which has a Shimano 7-speed hub but came without a shifter. It has lost its label but I assume it is a Nexus although I think quite old and the cable is attached into a chromed housing and clamped with a hex-socket grub screw; this differs from any Nexus illustration I can find on Google, so it may be something which predates Nexus.
Having never seen anything other than SA AW or Rohloff hub gears before, I blundered on and connected a 7-speed (cheap and old Shimano) twist shifter and just nipped-up the cable so there was no slack in gear 1 (or 7? can't remember if it defaults to low or high gear.) It appears to work in that it drives in each gear position (on the shifter) although I haven't ridden it enough to conclude absolutely it is selecting the full range although I would expect slipping in some shifter positions if it were not. The red marks certainly don’t align in gear 4 (on the shifter; more like 2/6) as Shimano guide suggests for cable adjustment on Nexus7.
So it appears that the cable pull is the same for a 7-speed derailleur as for a 7-speed hub gear and my life is made easy. I am suspicious however as this seems too good to be true from that ever divisive manufacturer; they are not usually that obliging in component compatibility.
I can’t find much information about cable pull requirements or anything other than standard shifters so wonder if anyone has tried similar substitution previously and what worked.
Shimano 7 speed hub gear
Re: Shimano 7 speed hub gear
sorry to be the bearer of bad news but the only shifter that will work perfectly with a Nexus 7 hub gear is (wait for it) one meant for a Nexus 7 hub gear.
What you have there is the first version of the nexus 7 gear which used a different cassette joint and axle assy to later ones. This arrangement is more robust in some ways because the cassette joint is retained using a metal circlip (so doesn't wear like later versions) but weaker in others because the axle has flats at one end only and therefore will only take a NTW at one end. Later versions of the N7 gear have two NTWs which is a better arrangement.
The cable pulls are ~5mm per gear between gears 1-5 and 6-7. Between 5-6 there is a longer cable pull of about 6 or 6.5mm. Not even an N8 shifter is right for it; that has a long pull between 4 and 5. The only other shifter which comes close is a SRAM X-series 7s or 8s shifter (which more or less pulls 5mm per click on every shift) but this of course doesn't have a long cable pull between 5 and 6. A shimano 7s shifter pulls about 3mm per click so will be a mile out, you will probably only get five gears from seven shifter positions.
If you are used to older hub gears you will be used to the idea that there will be neutrals between gears and that kind of thing. None of that with an N7, there is always a 'backup gear' so unless something is broken you should get some kind of drive regardless of how badly adjusted the shifter is. This doesn't mean it is OK to use the hub when the adjustment is wrong; if you hear funny noises or the gear hunts at all it is only a matter of time before the thing breaks.
cheers
What you have there is the first version of the nexus 7 gear which used a different cassette joint and axle assy to later ones. This arrangement is more robust in some ways because the cassette joint is retained using a metal circlip (so doesn't wear like later versions) but weaker in others because the axle has flats at one end only and therefore will only take a NTW at one end. Later versions of the N7 gear have two NTWs which is a better arrangement.
The cable pulls are ~5mm per gear between gears 1-5 and 6-7. Between 5-6 there is a longer cable pull of about 6 or 6.5mm. Not even an N8 shifter is right for it; that has a long pull between 4 and 5. The only other shifter which comes close is a SRAM X-series 7s or 8s shifter (which more or less pulls 5mm per click on every shift) but this of course doesn't have a long cable pull between 5 and 6. A shimano 7s shifter pulls about 3mm per click so will be a mile out, you will probably only get five gears from seven shifter positions.
If you are used to older hub gears you will be used to the idea that there will be neutrals between gears and that kind of thing. None of that with an N7, there is always a 'backup gear' so unless something is broken you should get some kind of drive regardless of how badly adjusted the shifter is. This doesn't mean it is OK to use the hub when the adjustment is wrong; if you hear funny noises or the gear hunts at all it is only a matter of time before the thing breaks.
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
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goatwarden
- Posts: 701
- Joined: 20 Nov 2009, 12:03pm
- Location: Bristol
Re: Shimano 7 speed hub gear
Thanks Brucey. Despite proving that I haven't fixed it, you have answered all my unknowns thoroughly.
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jakevoelcker
- Posts: 3
- Joined: 26 Feb 2015, 8:03am
Re: Shimano 7 speed hub gear
I used a Sram 7spd shifter on my Nexus 7 commuting bike for about 2 years, and it did work. However (as with any shifter intended for derailleur gears) the Sram shifter had a built-in overshift which is bad news for hub gears. I had to be careful with every gear change to take the shifter only just about to the click and no further. Eventually my hub internals detroyed themselves, possibly partly because of the shifter. I now have a new hub and the correct Nexus shifter and it's much better. The shifter is only £15 brand new at full price, and may be available cheaper online, so from experience I'd highly recommend that over bodging it with any other shifter.
Re: Shimano 7 speed hub gear
interesting point about the overshift. I just did a quick comparison between
- A current N8 twistgrip (almost identical in construction to the current N7 one)
- A ST-7S20 trigger shifter (similar to ST-4S20)
- A SRAM 7s trigger shifter
I found that I could overshift on upshifts (as would be with an N7 hub, i.e. pulling cable into the shifter) using any of them, but with the N8 shifter I usually didn't very much, I nearly always did (by 1mm and no more) with the ST-7S20 trigger (mainly because it is one-shift-at-a-time with this one) and with the SRAM trigger it was nearly always between 1 and 3mm overshift.
I'm not sure that the overshift is disastrous on an N7 hub because with any shifter it will only happen on an upshift anyway, and for it to actually do any harm I think you would have to be upshifting under appreciable load. I can think of lots of other reasons why an N7 hub internal might have clapped out in regular commuting use, mostly because of water ingress and bad (i.e. non-mobile) hub lubrication. There are better ways of lubing these internals than the method that shimano uses.
Of the many shifters I've used with these hubs I am not immune to the charms of a twistgrip but I do prefer the ST-7S20 trigger (now no longer available new, sadly). The current N7 twistgrip shifter is not terribly robust, nor does it have a wonderful action. But for a new shifter, it is pretty much the only game in town.
I actually have a a couple of SRAM shifters that I intend to modify so they have the correct cable pull for gear 6 and gear 7. I think it is going to be a lot of work for perhaps little reward....ho hum....
cheers
- A current N8 twistgrip (almost identical in construction to the current N7 one)
- A ST-7S20 trigger shifter (similar to ST-4S20)
- A SRAM 7s trigger shifter
I found that I could overshift on upshifts (as would be with an N7 hub, i.e. pulling cable into the shifter) using any of them, but with the N8 shifter I usually didn't very much, I nearly always did (by 1mm and no more) with the ST-7S20 trigger (mainly because it is one-shift-at-a-time with this one) and with the SRAM trigger it was nearly always between 1 and 3mm overshift.
I'm not sure that the overshift is disastrous on an N7 hub because with any shifter it will only happen on an upshift anyway, and for it to actually do any harm I think you would have to be upshifting under appreciable load. I can think of lots of other reasons why an N7 hub internal might have clapped out in regular commuting use, mostly because of water ingress and bad (i.e. non-mobile) hub lubrication. There are better ways of lubing these internals than the method that shimano uses.
Of the many shifters I've used with these hubs I am not immune to the charms of a twistgrip but I do prefer the ST-7S20 trigger (now no longer available new, sadly). The current N7 twistgrip shifter is not terribly robust, nor does it have a wonderful action. But for a new shifter, it is pretty much the only game in town.
I actually have a a couple of SRAM shifters that I intend to modify so they have the correct cable pull for gear 6 and gear 7. I think it is going to be a lot of work for perhaps little reward....ho hum....
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Re: Shimano 7 speed hub gear
Could you use a friction thumb or bar-end shifter?
Re: Shimano 7 speed hub gear
the problem with this is that it is very likely that you will end up between gears at times. You won't lose all drive immediately but the chances are excellent that the hub will be damaged.
In the simplest terms when the gear is half-in, it is like having a freewheel where the pawls are only half-way into full engagement; basically it is going to slip under load and when it does so it is liable to cause damage.
cheers
In the simplest terms when the gear is half-in, it is like having a freewheel where the pawls are only half-way into full engagement; basically it is going to slip under load and when it does so it is liable to cause damage.
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
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goatwarden
- Posts: 701
- Joined: 20 Nov 2009, 12:03pm
- Location: Bristol
Re: Shimano 7 speed hub gear
I was at the recycling project today and we decided the bike was not worth the effort for the project (ordering new shifter, time spent fitting, etc. would wipe out any profit for the charity; we could spend our time there more usefully.) So I bought it as a pile of bits and will sort it out at home.
I have just ordered a new shifter and chainset (both seem ridiculously cheap; chainset desirable as bike currently fitted with double chainset, front derailleur and rear fixed derailleur as chain tensioner) and so hopefully will be able to make it all work and look much tidier. Hopefully it will make a good bike for my niece to use at university.
The bike was a dead loss for the project as the frame has no mounts for rim or disc brakes at the rear (Nexus hub has a coaster brake) so we didn’t have any other suitable cassette or freewheel wheels in stock.
I have just ordered a new shifter and chainset (both seem ridiculously cheap; chainset desirable as bike currently fitted with double chainset, front derailleur and rear fixed derailleur as chain tensioner) and so hopefully will be able to make it all work and look much tidier. Hopefully it will make a good bike for my niece to use at university.
The bike was a dead loss for the project as the frame has no mounts for rim or disc brakes at the rear (Nexus hub has a coaster brake) so we didn’t have any other suitable cassette or freewheel wheels in stock.