So here’s the deal. I’ve been swapping out cranks on my 2nd generation pre-KH Shlumpf. For thousands of miles every thing has been hunky dory. I went from Schlumpf 165 mm cranks to some other brand of 152 mm cranks with no Q factor. The no Q factor was a bit scary for me. It made it too easy for my heels to hit the shift button by accident. So a few days ago I got rid of those cranks and put on some ProWheels 152 mm cranks. Lots of Q, I feel safer now. Except that today and yesterday when I was riding along in low gear at a high cadence the hub acted like it shifted. It went into free wheel mode for just a few degrees of rotation and then maybe went into high gear for a second at the most and then right back into low gear. On both occasions I maintained balance and kept riding, which is not so much a testament to my skills as it is to the brevity of the whole experience. Because it happened so quickly, and of course there was no warning, I’m not absolutely sure that it went into high gear. Something definitely slipped, though. It was one of those freaky scary experiences. The first time it happened I thought that maybe I had hit the shift button by accident, even though I didn’t feel any contact with my heel. The second time I’m absolutely sure I didn’t. Two times in two days is far too often to ride this around town and feel safe.
Has anybody else had this experience?
Do ProWheels cranks not work well with Schlumpf square tapers for some reason?
Any ideas about what is going on?
Just to add a little stress to my situation, I’m hoping to ride a century in a week and a half. I honestly don’t know if I can trust this hub right now.
Thanks in advance for the contributions from the best and the brightest.
The most likely explanation is that your bearing holders aren’t tight enough, so the lever arm slipped under torque.
It could also be that your cranks are loose or otherwise not installed properly. If a crank puts outward pressure on the schlumpf button, bad things happen.
Another possibility is that you put the buttons (or one of them) too far on the shift shaft after you changed the cranks. That way, the shaft cannot move completely to one side because the button on the other side is holding it back. So it may be just engaged in either high or low gear and could haphazardly disengage for a while.
Make sure that in each of the gears, you can push the “in” button somewhat more “in”, and it springs back when you release it. Just a little play is enough, like half a mm or so. If that is OK, you can rule out the above possibility.
i second everything that’s been said. if you’re still coming up empty you might check this out:
on my most-recent-generation schlumph, i managed to loose a little cir-clip that keeps the bearings from sliding along the axel. there’s a little lip on the axel next to the bearings where they sit. when mine was missing, my wheel would engage in geared mode all the time. when in 1to1 mode, it would engage for a moment then freewheel after a few revs.
it’s a long shot but maybe worth a glance if nothing else is working for you.
Doesn’t the “pre-KH” hub have a torque arm attached to the frame rather than the knurled “bearing”? I thought they only changed to the new method when the KH was released.
Is it? I thought it was an extension of the sun gear, to hold it still… I suppose it has a bearing inside it though for the axle to rotate. Anyway, getting off-topic.
Thanks guys. I really really appreciate your diagnostic efforts!
My hub, being a pre-KH Schlumpf, doesn’t have the knurled “bearing” or bearing. Whatever it is. It has the torque arm that is bolted to the frame. Yes, it is still bolted there. Good idea Tom, but it looks like that’s not what is going on.
Best I can tell the cranks are firmly attached. I didn’t ride it to work today because riding through traffic with an unpredictable Schlumpf is not good for longevity, so I can’t run out and double check crank tightness. I’ll check when I get back home tonight.
Klaas, I definitely wouldn’t have thought of that. I think the buttons are positioned relatively far out, so I don’t think that’s the problem, but I’ll check the button position when I get home tonight as well.
Mango, I’m putting my money on your diagnosis. I have noticed some clicking down there that could be due to the bearings slipping from side to side. The bearing spacer washer things are in place. That much I know. But they might not be thick enough to keep the frame and bearings from sliding around. I’m not sure how this movement would result in the gears shifting, but I still think that that might be what is going on. I’ll look to see if the circlips are in place. If not, I’ll make sure that they are and see if that fixes the problem.
Thanks for all of your insights. It’s amazing what kind of technical knowledge that the unicycle brain trust can provide. You guys are awesome. I’ll let you know what I find. It looks like there’s hope for Reach The Beach.
I must admit I’m getting on slippery terrain myself (as I am not aware of all the innards’ details), but it might be a matter of definition. Maybe that thing is a bearing whose outer shell is attached to the sun? I don’t know, I might be the muppet here.
Mango,
It looks like you were right! A big thanks. You are a life saver (not the candy, a real one).
The pre-KH Schlumpfs have bearings that are 90 mm apart. The Nimbus frame from which my frame originated, has bearing holders that are 100 mm apart. Rather than just sqeeze the frame the 10 mm closer, the guy who reconfigured the Nimbus frame into what is now my V frame, removed the circlips and added a total of three washer-like spacers. When it was all assembled with the original Schlumpf cranks everything was just fine. The Schlumpf cranks seat closer to the bearings than the new Prowheels cranks, therefore the Schlumpf cranks kept the bearings and the rest of the hub nice and tightly packed together. When I switched to the Prowheels cranks there were a few more millimeters of play for the bearings to slop back and forth.
So I took everything apart to investigate the circlip issue. I detached the torque arm from the frame. Then I removed the wheel set from the frame. As I was tilting the wheel, the torque arm, which is attached to the sun gear just fell off the axle. Whoops. With the cranks off, there wasn’t much holding it in place.
So what was happening when I was riding around with the Prowheels cranks was that the bearings were sliding back and forth. Sometimes the bearings spread apart far enough so that the sun gear became completely disengaged from the planet gears. That’s when things went funny/scary and it felt like I had switched gears. A split second later the bearings came back together and the sun gear re-engaged and everything was normal again. That’s my theory anyway.
So I reassembled the hub, left out the spacers and installed the circlips. I’ve only ridden about 4 miles since, but I haven’t experienced any problems.
Looks like the Century is on for next weekend!! Woo hoo! No excuse now for bagging out. Except for the boo boo on my knee.
So a big thanks to all of you who came up with the great suggestions and your detailed Schlumpf hub knowledge. What a great community we’ve got here!
My heirs thank you too.
Mango, I have the same problem. Where did you get a new cir-clip to snap in?
Also, my axle shaft is somehow tightly pressed in so that the groove for the cir-clip is inside the hub and completely out of view. It is too tight to simply pull by hand. Did you have the same issue? How can I pull out the shaft?
See my Thread for more details: Slipping Schlumpf and short axle??
