A couple of weeks ago my chain snapped whilst out riding.
After being rescued by car by my husband I changed the chain and did some general trike fettling, after which it became clear the chain was skipping over the rear sprocket (the sprocket had done 11,000 miles and was therefore probably rather worn).
Clearly I needed a new sprocket but had no idea how to go about changing it or whether any old sprocket would do.
So I sent an email to the ever-helpful Huw at Madison and he replied:
Basically, it’s a very easy job, you don’t need any specialist tools, just a few spanners and a screwdriver, you will need to remove the cassette unit (the plastic device that the cable routes into).
After taking the cassette unit off (part CJS-700 on the exploded view) you just need to prise a circlip off with a screwdriver, there should be a few notches in the hub where you can get purchase on the circlip.
Once the circlip is off (the circlip will be very tricky to get off) it is just a matter of taking the sprocket off and replacing it on it’s splines, then re-fitting what you’ve removed.
I have attached the exploded view for your hub and the Service Instructions which briefly explain the task, if you’ve done the servicing I’m sure you will find this an easy task.
So, fortified by the knowledge he thought I’d be fine, I went ahead and ordered a new 18T Alfine Sprocket (part number CS-S500, the Shimano Alfine Single Sprocket with Chain Guide 18 Tooth Black/Silver) which was just £7.99. Not a bad price at all!
The part arrived but I held off doing the sprocket change until a day when my husband would be around to help me. Mindful of Huw’s warning about the circlip I thought trying to do it myself with one weak arm might be a bit risky.
So today was the day – James had a day off work, the sun was shining and it was time to do a bit of trike maintenance!
So this is the view of the trike hub attachment in the lowest gear.
In order to remove the rear wheel you need to first disconnect the cable attachment for the hub gear. You can see here how the cable is attached to the hub – a notch in the hub assembly traps a metal widget.
And from the side.
The trigger shifter shows I am in the lowest gear.
In order to disconnect the gear cable and remove the rear wheel you have to first put the hub into top gear (11th). Fortunately with an Alfine you can change gear whilst stationary.
And this is what the cable now looks like going into the hub – the rubber bellows have extended and the cable is wrapped right round. The widget holding the cable is now right underneath the hub.
Here is the view from the back.
As the cable is so long it’s easy to grab it and pull and so rotate the gear innards upward, leaving the cable slack. I tend to find with my finger the place where the widget is attached and rotate it round, rather than pulling the cable, but either way works. This way is oilier though!
I’ve rotated the cassette unit right round now (as if it’s in first gear) and you can see how much slack there is in the cable.
It’s easy to pull the cable out of the guide area and disconnect the widget so it’s all loose.
Here is the hub now unattached to its gear cable. I try to put the gear cable out of the way but it has a terrible tendency to get in the way whilst you’re trying to remove the wheel!
Next thing to do is remove the blue and green axle washer thingies so that the wheel can be removed. Green for the right (starboard), blue for the left. You can see on the photos that they have a notch that is what stops the axle turning when you put the wheel in – the central hole is not round but shaped and this keeps the wheel in position. Blue and green washers are for vertical dropouts (which is what I have on my trike).
And here is the axle without the bolts. Note that the bolts are chewing away at my gear hanger!
And the other side (I forgot to clean this side before the photography!)
And now the job I hate – removing the wheel. I find this is always difficult for me, on a trike with a normal derailleur or with a hub gear. There’s something about trying to work your way round a derailleur/chain tensioner that just doesn’t work well for me!
However, on Alfie there is a more significant issue which causes more of a problem – my chain tensioner/Sora derailleur always instantly grips the carrier (the plastic guide either side of the rear sprocket) and won’t let it go.
I struggled with this for five minutes before calling James to help me. He was able to sort it out for me as he’s more adept but this is something that worries me about getting a rear wheel puncture when out on my own – will I manage to get the wheel off on my own? Fortunately I’ve only had 3 rear wheel punctures in 37,000 miles so they aren’t that common (and only one was when I was on my own and I managed).
Part of the problem is that my Sora derailleur has partly seized. When we changed the chain two weeks ago James spent ages freeing it up but once again it doesn’t want to rotate at all – you can see here a photo of the offending bit with an allen key stuck in it (I was hoping to remove it to give it a bit of a clean but it was not possible to undo it).
This bit should swing forward and backward to help tension the chain; it’s stuck in its mostly forward position which means it doesn’t get out of the way properly when trying to remove the wheel (plus the chain is a bit slack when in the granny ring).
And the main reason we’re pretty gentle with it? The gear hanger that it is attached to isn’t as strong as I’d like (I have previously broken one) and I don’t have a spare. I shall get on the phone to ICE and order one before I have a proper go at removing this part but I think this chain tensioner doesn’t like not moving very much.
So I now have a trike minus its rear wheel and after a spot of lunch and a cup of tea it was time to attack the hub.
Here it is in all its glory.
First job is to remove the topmost bit which has the large yellow dot on it.
This was dead easy – just rotate it anticlockwise and it undoes.
The next bit to remove is the cassette unit (the thing with the sticking-out arm).
This just lifted straight off!
This was all seeming rather easy so far.
Next item is a little rubber ring thingie.
There were warnings on the Shimano info document to put this on the right way up so I carefully placed it on my bit of cardboard so I knew which way up it should be.
And this is what we now have. The sprocket and its carrier are now just held on by the Circlip Of Doom.
Right at the bottom you can see the notch in the circlip. This was all we had to help ease the thing off.
James attacked it with a screwdriver.
And then with two…
Success! The thing was removed in just a couple of minutes.
Now the old sprocket just lifted straight off.
Here’s the mucky hub without the sprocket.
Old sprocket (on the left) and new on the right.
We cleaned the spindle etc of oil and gunk and random bits of hair! Much better.
The new, very clean sprocket and its carrier slotted straight on.
And now, the Circlip of Doom.
Taking it off wasn’t as bad as we had feared, putting it back on was a bit of a struggle.
We got it started OK.
And then you get to this point – we had to nudge it down so that it was on the very bottom of the pile of things on the spindle. You can see the two ends of it indicated by the arrows – not there yet!
And here’s the pic without arrows.
Did it!!! Only took about ten minutes.
So now it’s easy putting it back together – first the rubber ring thingie (that I had kept the correct way up). I cleaned it up a bit before replacing it.
Before I put the cable cassette thingie on I decided to give it a clean.
Couldn’t get all the gunk out so we took it apart (two tiny screws) and that helped a lot.
Once screwed back together again, we just had to line up the red dots on the carrier and the spindle and it all went in place. Then it was lining up the yellow dots for the outer metal widget and everything clicked into place beautifully.
A side view of the lovely clean sprocket!
Now all we had to do was put the wheel back on the trike. This went better than I had expected (well, I got James to help me from the beginning).
The difficulty (apart from fighting with the derailleur/chain tensioner and lots of mucky chain) is ensuring the arm thing is in the correct place. It has a real tendency to twist itself into the wrong position and get stuck. We managed to overcome its perversity this time without too much hassle.
Once the wheel is firmly in place we add the green and the blue non-turn washers either side, then tighten the bolts each side of the axle.
And then the last thing – to attach the gear cable! This involves once again sticking my finger underneath to rotate the top widget thing (with the yellow dot on) to bring it round so that the hole for the cable widget is there and I can slot the cable in. Then it is slowly released and all is done!
I haven’t had a chance to test my new sprocket except for cycling across the front lawn (about 10 metres) but the chain didn’t skip for that distance so it looks like it’s been a success!
[EDIT] All works very well! Took it out for a 26 mile ride today and the new sprocket works excellently [END EDIT]
All in all this was a pretty painless task and not as mucky as I suspected either.
The entire kit that I have removed is available to buy separately for under £14 so I think next time I’ll treat the trike to a new one of these too.