Is my Schlumpf hub broken (again)?

2 days ago, I was riding uphill at Elsbet. As I was riding in first gear, I went freewheeling. It reminded me of last year, when I was taking part in the Mont Ventoux Unicycle Challenge: my hub went freewheeling a lot of times. I didn’t know yet, but it was broken. Florian took it apart and have seen that the inner mechanism was severely wore down. He replaced it and it went nice since then.

So, is my hub broken - again?

For information, my right crank, on which the up-shift button is bolted, was a bit loose. Not so much that I could feel it while riding, but still a bit. I know this can explain some freewheel issues, but I’m not sure if it can explain this one. As far as I know, when a crank is loose, its bolt can push on the button to the outside and this could lead to freewheel. Does this apply to all the configurations? Which would mean all of the following freewheeling situations would be possible:

  • up-shift button on right crank, right crank is loose, low gear (<-- my situation when I went freewheeling)
  • up-shift button on right crank, right crank is loose, high gear
  • up-shift button on right crank, left crank is loose, low gear
  • up-shift button on right crank, left crank is loose, high gear
  • up-shift button on left crank, right crank is loose, low gear
  • up-shift button on left crank, right crank is loose, high gear
  • up-shift button on left crank, left crank is loose, low gear
  • up-shift button on left crank, left crank is loose, high gear

The previous question can be summarized to: “if any crank is loose, whichever crank the up-shift button is bolted on, whichever gear you’re riding, you may go freewheel”. Is this right?
If this isn’t right and I should not have gone freewheel in such a scenario, then I may have to disassemble my wheel and send my hub back to Florian :frowning:


Sorry to hear this Maxence :disappointed:

Can I check have you tried mounting a brand new set of cranks?

I’m thinking this is the 800 series BrakeFast hub right?

When you mount the cranks are you using the pre-tightening bolt?

I just wonder if you’re suffering more from a dodgy tight crank and its interface is just going to keep causing you issues.

I have never experienced this but I get the idea of the shifting button not enjoying a crank that doesn’t allow it to fully engage.

Again non-engineering brain wonders if there is a spring that is either too weak or too strong in your hubs internals causing it to not full engage or disengage.

I have had a misshift when my new hub kind of freewheels but this is not the same as shifting up (button goes in) and then the mechanism freewheels - which is what I believe you experienced

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You didn’t accidentally half-hit the button, by any chance?

I’m just learning how to ride a Schlumpf, and have done that a few times - either brushed the button accidentally and half-shifted-to-freewheel, or had the button screwed in too deep so when I tried to shift it didn’t go all the way in. And freewheeled. I don’t have any basis for comparison since I’ve only been riding it for a couple weeks but I think it’s all me and not the hub :slight_smile:

– UniT

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Just to clarify - if the crank was loose, was the button not able to travel all the way in, perhaps? I don’t know if you were deliberately shifting when it freewheeled or not. But if you were, I could see how that might do it…

– UniT

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I dont understand your list of setups, but, I might be able to answer.

Technicaly, if the crank of the side where you need to press to up-shift is loose, that means you will not fully engage the high gear and might end up in freewheel. You can damage the engagement points inside when doing that. And when that happens, it can freewheel whenever shifting in whatever direction.

It’s VERY VERY VERY important to always have a little bit of play behind the button once it’s engaged in the gear we want. Not having play means the engagement points are not 100% in and can cause damage to the hub.


Thank you all for your replies! :slight_smile:

Not yet. The cranks I use have already been used for some time. I’m in the process of finding new cranks to be sure the issue does not lie in the cranks being too old.

Absolutely right!

I’m pretty sure I didn’t. Even though I had, I’m pretty confident I would have been able to stay on the uni.

I was definitely not trying to shift. I had downshifted a few seconds before, though. Maybe the shifting process didn’t work well because of the crank being loose.

The issue is that I wasn’t even trying to shift. I was just riding normally, in low gear.

I do remember you telling me the exact same thing 4 years ago. So I now pay attention when I mount my cranks and screw the button :grin:
However, in that case, the crank may have been loose for a bit of time and the hub may have been damaged by my riding style :fearful:

Anyway, I’ll try and mount new cranks. I’ll let you know in a few weeks - or months, if I don’t ride my G29 so much in the next weeks - whether the issue was the loose crank or the hub itself.

Thanks again for your help!

Wondering if the loose right crank is therefore pulling the shifting rod towards to right - which would make the left (“low” button) snugged into its space - as in it would have little to no ‘pressing’ space.

So the question would then be: is the pressing space needed only for a good shift or also for how the hub remains engaged in any state - low or high gear that is.

I’m going to say it probably does make a different as the ‘in-gear’ state is when the shifting rod is stationed in the locked in mode for whatever gear - and not pulled or obstructed in any way regarding the extra inward pressing space.

So a loose crank on any side will be bad for shifting from any direction and also bad for running in-gear, low or high.

I may need to drink a second coffee and come back and edit this - but what I’ve typed so far feels like to makes sense.

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Thanks for the insights! That’s what I would have also said.
I have also tried something to check whether this stands or not. While pushing the left button - so, this should be similar to pulling the shifting rod to right -, I have pedaled with one hand… And the hub didn’t freewheeled. But it may only freewheel when lots of pressure is applied on it, which would explain why it did freewheel while riding uphill. So… Lots of unanswered questions :grimacing:
I may send an email to Florian to understand more about how the hub works.

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The missing part in understanding I feel is how the gear is locked in / engaged. Something is holding that in place or it holds itself there when engaged - but then what is the item that allows it to disengage.

I keep picturing a spring with two ball bearings from my countless watches of the How It’s Made video.

I bet there’s a correlation between drive forces and how well this engaged mechanism can hold the locked in gear - and I’d second bet this system isn’t effect or secure when there’s any away-tension to the shifting rod - towards to non-engaged gear. High or low that would be.

(That tension I see as coming from your loosening crank pushing in the inside face of your button and effectively pulling the rod say from high to low)

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You are right, if the button bottoms out (or the crank bolt comes out), it pulls the engagements out. There’s only about 2mm of engagement inside, the mechanism is the exact same when engaging Low or High gear.

Something I have seen on a pre-800 serie hub, was that at one point for a short amount of time one of the crank bolt came loose. That lead directly to damaged engagement pins. The issue was though, as soon as the pins were damaged, there was bits of broken metal floating around the hub. The pins are inserted with a very tight tolerance. Those metal bits ended up getting stuck in some engagement pins, leaving only 3 pins working out of the 8! I had to take appart the hub completly, clean out every bit of lube there was and making sure everything was dry and clean, then rebuilt it with new lube. It’s been good ever since. That happened about 6 months after getting the hub, and the hub is now something like 8 years old?

This is what I mean when as soon as you get issues, it doesn’t matter which side you are shifting. If you have metal shavings floating around the hub there’s no other solution than a complete rebuild.