Aaaagh - broken flange on my Schlumpf

Was just making the final tweaks to spoke tension having fitted a new rim to my first generation Schlumpf and the flange broke at a spoke hole. Don’t think the tension was excessive (it was pretty similar to the tension on my other 29er wheel - admittedly higher tension than the previous build, but that was leading to spokes going completely slack), and no sign of any notching at the spoke hole where it’s broken, so not really sure what I did wrong.

Is there anything I can do with this, or is my hub now trash?

I’ve read suggestions of making a plate to span 3 holes on the hub bolted to 2 bridging the popped hole. Then with hole for those 3 spokes drilled in it

Those 3 would be a little shorter but might work

However practically I’d probably just run my hub missing 1 spoke. Not perfect but better than binning the hub

Can it not be sent off to get fixed? Though that may be a costly fix.

I’ve sent an e-mail to Schlumpf - will see what they say. Not really sure I can see how it can be fixed short of replacing the whole hub body, and given it’s a first generation they probably don’t have lots of those sitting around :frowning:

Maybe he’d upgrade you for a reasonable cost?

That’s a bummer. I wonder if Schlumpf will improve that area as well in the next version of the hub. Hopefully…

Actually that might just work - I’ve seen the suggestion to bridge the gap but use the existing spoke holes and the existing spokes to hold the plate in place, but not sure a plate thin enough to fit will be strong enough. However if I bolt a new plate in it can be a lot thicker, and actually the spoke length will be virtually the same with a 3 cross spoking.

Though looking at what I have, I think there’s a better plan. I actually only need to take out the spoke to the left of the break in this picture - if I use a steel plate bolted onto that hole to attach both the spokes, the force from those spokes will counterbalance each other and the net force on that spoke hole will be a lot less than that normally at a spoke hole. Odd length spokes required, but I think I can love with that.

And how about drilling a new hole in between the broken out one and the next one on the left? Maybe that could be another solution?
Very limited room though…

Yeah, that’s the problem - not even as much room as it looks from the outside as the hub body is higher on the inside. If it wasn’t cut away between the spoke holes it would be an obvious and easy fix.

It just might fit. The actual hole would be a little smaller than the marked spot.

I’m not sure that you will have a net loss of tension with two spokes pulling on a single hole. It’s true that the force will be somewhat opposed; however not directly. What about building the flange back up with aluminum brazing rod? I’ve never used the stuff but if the infomercials are even half right it may be strong enough. Of course you’d have to strip down the hub, and repack it. Probably a rebuild for the wheel too.

Same thing happened to me, just been riding it. Though about maybe trying some JB weld but I dunnno.

It has been reinforced on the last production and additionnally the radius is now machined on both sides of each holes. My feeling based on the photo is that your wheel has been built with the spoke radius on the wrong side of the hole radius machined on the hub.

I’ve posted this in the STW thread but I though this might be of interest here, too.

If you want a ‘proper’ repair then you could get a new flange laser cut. Basically an annulus with two concentric rings of holes: one set for some m3 bolt to fix into the existing spoke holes and a new set of holes for the spokes. You’ll probably get away with same spokes and it would only cost £10-£20.

Something like this:

You might have to play with the outer hole positions a little to keep the same length spokes, and the inner pattern is just an approximation.

Ah - shouldn’t be surprised to find you on here too! I thought I might get slightly broader technical expertise on STW, but as it turns out the two best suggestions have come from unicyclists.

Not in that photo it’s not - I’d just rebuilt it the right way round (previously one side was wrong)! Though I think where it has broken is on the side where it was always right.

I had the same thing happen to my older generation square taper Schlumpf hub. I sent it back to Florian and he replaced the hub with a new ISIS hub, though this was not free. Hub number 105 was replaced with M501 - their serial numbers pleasingly reversed!

When applieng such one I would skip each time 11 holes until all bolts are tight.

Should probably give an update on my plans for those interested. I like nickjb’s idea as it takes a lot of the stress off the spoke holes, but for now I’m going with something a lot simpler. I mentioned earlier the idea of using a plate bolted to the spoke hole to the left of the broken one with two spokes attached with opposing tension. A slightly more elegant development of that was suggested to me by a chap called Ben from Kinetics cycles (who is himself a unicyclist).

I’m going to get an extra long double ended spoke made up with an s-bend in the middle and threaded at both ends. The s-bend will sit in the intact spoke hole to the left, one end will act as a replacement for the spoke currently in that hole, the other end will replace the spoke which would have gone in the broken spoke hole. I’ve had a good look at the forces involved, and at the worst the force on the spoke hole from this double spoke will be no more than that from a single spoke - provided neither of the spokes ever goes completely slack (as they shouldn’t do in use) the force on the spoke hole will be less than normal.

After searching around for a way to make such a double ended spoke I eventually found an obscure specialist shop which sold something suitable…

It’s a fairly common problem on the earlier hubs. I had a 2008 KH/Schlumpf hub which was hardly used before it broke.

The problem is that the flange holes are directional- if you don’t have the spokes around the right way it puts too much tension on the flange and snaps it.

Mine broke a couple of weeks after a new wheelbuild, and just before my races at Unicon 16. Luckily I managed to buy a new hub and had my wheel rebuilt, but it was still pretty annoying.