Problem with my new Schlumpf guni hub?

Unicycles and Equipment
1

In a nutshell, one of the crank arms is loose on my (new) Schlumpf guni hub. This is the same problem I had six months ago with my first generation hub.

The loose arm is on the downshift-button side. That is the same thing that happened to me last time, if I’m not mistaken. Luckily for me, a fellow member of the NYUC also has a guni from Florian, so he may be able to fix this when I see him tomorrow. If not, I’ll have to disassemble the wheel again (that’s a lot easier than building it!) and send the newer hub back to Switzerland.

I should note that I have not gone down any big curbs (nothing more than a few inches, and only a few times). I think the only strain I put on the guni was while riding up a fairly short hill today in high gear.

Blah blah blah:
Back in October, my geared unicycle began having problems. On several occasions it slipped out of geared (once causing a scary fall), but worse still was the related fact that one of the crank arms was falling off. I emailed Florian and spoke with him a few times in Switzerland, and I tried repairing things on my own and with the help of fellow NYUC club member (and fellow guni owner) Dave Bagley, but finally we realized that there was no way to fix this unicycle’s hub.

Florian had been working on an improved hub at this time, so rather than trying to fix my hub or sending me a replacement, he generously decided to give updated hubs to all owners of 1st generation hubs. These newer models have 12 internal pins rather than 6, and this means that the hub can switch into gear more smoothly. It took nearly six months for the updated hub to arrive, and it finally showed up last week [Florian had broken his arm and had gone to Laos on a unicycle tour, adding to the delay.]

Once the hub arrived, I tried to rebuild the wheel (putting all of the spokes back on the rim), but my two attempts failed. Rebuilding a wheel is a Zen art, and I’m not even a Zen grasshopper when it comes to truing a wheel, let alone building one from scratch. So I paid a bike mechanic $35 for the job, and, as of Wednesday afternoon, was on my way. Sure enough, the shifting was nearly seamless. I was able to make transitions from low to high gear and back with little difficulty. I rode it to Brooklyn and back to my mom’s apartment on the Upper West Side (a trip of about 8.5 miles each way) twice, logging a total of about 36 miles on it until just an hour ago when I realized that one of the crank arms is loose.

The loose arm is on the downshift-button side. That is the same thing that happened to me last time, if I’m not mistaken. Luckily for me, a fellow member of the NYUC also has a guni from Florian, so he may be able to fix this when I see him tomorrow. If not, I’ll have to disassemble the wheel again (that’s a lot easier than building it!) and send the newer hub back to Switzerland. Ugh.

2

Hmmm… my left crank came loose during the Laos tour. We just assumed it was the result of not being put on tight enough by the bike shop that I had build the new wheel for me. After that day’s ride, I tightened it up and had no problem since. Though it’d probably be a good thing now to to go over it with a proper torque wrench and make sure it’s tight.

3

Wow. That’s a relief. So maybe I can take it to the bike shop down the block and see. Thanks for the note, Gilby. I’ll write back when I know more.

David

4

no relief

Well, I took it to the bike store, but here is the snag: The loose crank is the one off of the silver button, which is the one that does NOT come off with the special tool. Now, I have never taken apart one of these hubs, and I don’t have Florian with me, so I wasn’t sure what to do. We got the other crank arm off easily (the first time I’d seen what is behind a crank), but from there we had no idea what to do next. The other crank and the other button were just taunting me.

5

Are these cranks regular square taper? If so anti-seize the taper and the bolt or nut thread liberally tap firmly but not too hard with a rubber mallet and tighten the bolt/nut. Anti-seize is the key!

6

Schlumpf has manuals in PDF format for their bicycle geared bottom brackets. The manuals explain how to adjust the shifting buttons for depth in the cranks and other things. You can download the Mountain Drive manual here (scroll down to the bottom of the page). Print that out and the bike shop should be able to get the shifting buttons adjusted for you.

7

Thanks, John. I checked out the site and eventually found the right technical manual pages. Luckily I can take them to the bike mechanic tom’w (whether he’s available is another issue). I can also buy a torque wrench and try the work myself or with a club member.

I really hope I can get this taken care of HERE rather than in SWITZERLAND!

David

8

What length and brand of cranks are they, David?

9

i know this is completely off topic but with the splinded geared hub comming out in the summer. i was wondering if you can replace the axel or do you have to replace the whole hub?

10

Honestly, I don’t remember. The thing is in the car, anyway. I’m so annoyed about this. I think they were 140s or 150s, and I’m curious as to why you wanted to know.

Florian wrote me today, asking whether I had tightened the crank arms or whether he had. When I sent back my hub, I also sent back the attached cranks because I had no way of taking them off (or if I did, I didn’t know it). But D4 sent his hub back without the cranks, so maybe he will know what to do (when I see him tomw) or will have the tool for tightening the crank.

I assumed that the assembly would come back to me in perfect shape and that this issue would have gone away. It’s hard to believe I waited 6 months for this. I do know that the cranks seemed fine when I got the assembly back – otherwise the mechanic and I would have noticed the loose crank earlier. So I’m guessing that something went wrong within a few miles of riding the new assembly, which seems odd, but it’s my only guess. Is it possible that Florian used some of the same components when he gave me the new hub? Perhaps the cause of the loose crank was never dealt with and I’m just riding the same faulty crank? I wish I knew enough even to make a good guess (or at least to be able to explain it to a bike mechanic).

11

What I’d like to know is how you ‘tightened it up’ in the first place. At the store yesterday, the mechanic and I failed to figure out what to do in order to effect any tightening whatsoever. We managed to take off the crank that was already tight, but it didn’t allow us to get to the loose crank or to do anything about it. The mechanic was understandably nervous about doing anything that could make the situation worse – he’d never seen this sort of assembly before.

Also, what tool did you use for tighening? You alluded to a torque wrench, but Florian wrote to me about getting a torque screwdriver (the thin one that goes into the hole of the button). I take it that this tool is not commercially available other than thru Florian. So I’m not sure what to do (or what to tell a mechanic to do).

12

You need the uber tiny alen wrench to remove the button from the crank, then you just use a torque wrench to tighten the nut just like on a regular unicycle. The torque screwdriver is used to put the button back on and I used Florian’s since he was on the LUT. Oh, and when removing the button, don’t do what I did and unscrew the hex screw all the way. It’s soo tiny and would suck to loose that. You just need to loosen it and then spin the button off with your hand.

If you have the same cranks that you had on the old hub, it sounds like since the crank came loose before and you rode on it, you may have damaged the cranks, meaning that it’ll never stay tight now because they are deformed. That’s typical with alloy cranks when they get loose.

13

I went to the bike shop, which was not helpful bc they don’t carry torque screwdrivers.

D3, the cranks only say ‘Schlumpf Innovations’ on the outside, so I am guessing they are his own creations. I guess they are 127s, bc the number 127 was etched into the cranks.

14

we did all of that, and the nut we came across was good and tight.

Yeah, so I either have to return the cranks or the whole crank/hub assembly. The problem is that I can’t remove the cranks, tho I believe my fellow club member can help me with that tomw.

15

Well, I was just guessing that the axle design and fabrication is very fine, but that the cranks are added as a necessary afterthought. Since unicycling puts more strain on cranks than bicycling, I reasoned, then the cranks added are possibly not up to snuff. This is why I asked about the brand.

From the technical manual it appears that replacing cranks is a simple matter provided that one has a small set of Schlumpf-provided tools. I don’t know whether these come with a unicycle or must be a separate purchase.

It might be reasonable to replace the factory-provided cranks with a set that are more unicycle-tested. This is why I was asking about the length.

From the manual it is evident that there are dimension restrictions on cranks that may also affect one’s choice of cranks that are suitable for that hub. The best cranks for square taper axles tend to have beefed-up dimensions in the very area where the manual has restrictions.

16

There are just a few small tools that are provided with the uni. One is a tiny allen screwdriver attacment that is necessary in order to remove the button. Another is a two-toothed job that holds the other button in place so that you can twist the first thing around without it going in circles.

Here is my trouble: I can remove only one of the crank arms. The other one appears fixed, like it’s attached to the hub diff’ly. Can someone else please corroborate this for me?

17

http://www.schlumpf.ch/handbuecher/WHB.md.engl.pdf

Page 17 tells how to remove crank arms. This is for the mountain bike model. I do not know how this relates to the unicycle hub.

18

Thanks, D3. I have already printed out that page (and a few others), but as you noted, there is no photo about the removal of the cranks for the uni. Luckily for me, D4 has already removed the cranks from his uni, so I can work with him tom’w at the club to get that job done.

Florian was specific with me about two things: 1) He doesn’t have extra hubs – they’re all spoken for, which is great (I’m glad his work is getting so popular), and 2) He never replaced the original cranks which are causing the problem now (due to friction wearing them down the first time), so he wants me to put other cranks on, and I can do that tom’w, too, since D4 has an extra set.

So by tom’w evening, I may have this under control.

19

I would assume each side is the same as far as removing cranks go. There is a special “small tube” that goes over the shifting shaft that allows you to use a regular crank extrator to remove the crank. You didn’t mention that as a schlumpf tool you had, but it did come with the uni (or with the replacement hub when I got mine).

20

Huzzah

My only hope was answered today at the regular convening of my uni club. Dave Bagley, who among other things is the webmaster for Tommi Miller, had pulled a groin muscle while riding his sideways-riding uni, Crabby, which Tommi built for him recently.

Since Dave was unable to ride and since he is such a great guy, and since he is the only other owner of a Schlumpf geared uni on the East Coast, he volunteered to help with my guni this afternoon.

It turns out that the only difficulty I’d had was removing the button on the loose crank side. It turns out that both cranks are attached identically, but tho that makes sense, I wasn’t sure owing to the fact that this is a geared uni.

Dave was able to get this button off, but he said it was tricky. Once done, he could have either tightened my loose crank or replaced it with an extra one he had. And being Dave Bagley, naturally he replaced it for me gratis.

Now I have my geared uni back in anction, and I can fix it myself if a crank ever loosens again.

Thanks, Dave! And thanks, too, to Gilby, Stockton, and Childs for trying to assist, too.