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Old 2012-06-24, 07:51 PM   #1
MuniAddict
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Red face Super Schlumpf Slip 'n' Slide... accidental coast & bail!

Had a total bearing slip while riding my schlumpf G26er high gear this morning, in causing a rather long unintentional coast! As I was coming down the hill I applied some back pressure, and that's when it happened. Caught me by complete surprise but I somehow I managed to stay on for the coast, and thanks to quick reflexes, I had a surprisingly controlled dismount.

This kind of slip in high often results in a hard fall to your backside! I had my frame bead-blasted last week, which also removed the powder coating that from the inside of my bearing caps. This had kept the caps and the frame from contacting, so you could properly tighten the caps onto the bearings.

Unknown to me until this happened, without that layer of paint, I was not able to tighten the caps enough to keep the [knurled] bearing from slipping during back pressuring. The caps were tightening against the frame instead, allowing movement of the bearing. So now I will put some shims in there to take up the empty space!

Has anyone else experience the Schlumpf "slip"?


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Last edited by MuniAddict; 2012-06-24 at 07:57 PM.
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Old 2012-06-24, 08:10 PM   #2
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Nice catch!
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Old 2012-06-24, 09:27 PM   #3
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Yeah, once, just once

Nice face making there on the dismount
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Old 2012-06-24, 10:05 PM   #4
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That is exactly why I am going to bond my knurled bearing to a bearing cap once I get it back. Bond it to a cap and you don't have to worry about slip and don't need to over tighten.
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Old 2012-06-24, 11:19 PM   #5
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Quote:
Originally Posted by saskatchewanian View Post
That is exactly why I am going to bond my knurled bearing to a bearing cap once I get it back. Bond it to a cap and you don't have to worry about slip and don't need to over tighten.
I don't know if I'd want to do that! How would you remove the cap if you needed to, or to change frames? And the bonding agent would likely get caked into the knurling, making it difficult to remove if necessary. I'm thinking a thin strip (shim) made of fairly firm rubber would allow the knurled bearing to mold and settle into it, and prevent slippage. The rubber shim could be glued to the inside of the bearing cap and frame cap.

If that didn't work, then a traditional shim would suffice. Kris told me that I could also file the frame caps and bearing caps a bit, (where they come together) so it would once again create that small gap between the frame and bearing caps, enough so it would tighten onto the bearing, and not frame to bearing cap, like it would with no bearing inside!
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Last edited by MuniAddict; 2012-06-24 at 11:27 PM.
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Old 2012-06-24, 11:33 PM   #6
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Haha, once the video is loaded, Keep hitting number 4 on your keypad,, lol! (make sure you click somewhere on the video screen first, the hit 4 repeatedly! Or 5 for slomo!)
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Old 2012-06-25, 03:50 AM   #7
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I don't know if I'd want to do that! How would you remove the cap if you needed to, or to change frames? And the bonding agent would likely get caked into the knurling, making it difficult to remove if necessary. I'm thinking a thin strip (shim) made of fairly firm rubber would allow the knurled bearing to mold and settle into it, and prevent slippage. The rubber shim could be glued to the inside of the bearing cap and frame cap.

If that didn't work, then a traditional shim would suffice. Kris told me that I could also file the frame caps and bearing caps a bit, (where they come together) so it would once again create that small gap between the frame and bearing caps, enough so it would tighten onto the bearing, and not frame to bearing cap, like it would with no bearing inside!
I am planning on using a Mountain Uni UCM (Nimbus D'brake would work as well, as long as it has clearance) with its universal bolt holes. I may or may not remove the calliper mounting arm first since I was using it with the knurled bearing on the left. I see no reason to remove the bearing cap once it is on there if it can fit any frame I am likely to get (Triton, KH, Nimbus, Qu-Ax, K1, etc)


I am not so sure about adding shims, it might work but I would just remove a bit of material from the bearing holders like Kris suggested.
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Old 2012-06-25, 11:06 AM   #8
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I wonder if a little hole could be drilled in the knurled bearing and a corresponding pin or screw could be stuck in through the bearing holder to keep it in place. Wouldn't want to try it out myself, though. But something like that should be a pretty easy fix for the problem for Florian and Kris, also with the new disc cranks and the geared hub combination.
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Old 2012-06-25, 11:14 AM   #9
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I wonder if a little hole could be drilled in the knurled bearing and a corresponding pin or screw could be stuck in through the bearing holder to keep it in place. Wouldn't want to try it out myself, though. But something like that should be a pretty easy fix for the problem for Florian and Kris, also with the new disc cranks and the geared hub combination.
pin must be use only for precise positioning but not for torque resistance, next Schlumpf generation should have a better design if I understood properly the reason on KH2012 bearing cap modification (no more lip on the inside)
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Old 2012-06-25, 12:49 PM   #10
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Never had it during actual riding - only in the first few test spins after re-assembly. It does feel sketchy though!

A rumour is that the next version of the Schlumpf hub may have the bottom-half of the KH frame bearing housing built as a single piece onto what is currently the knurled bearing casing, which should rid us of any risk of this happening. It would also avoid over-tightening issues as you'll not be using any bearing-holder tension to resist the twisting force.
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Old 2012-06-25, 02:16 PM   #11
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Another way to hold it firmly in place would be to have the bearing cap knurled or grooved as well, (during manufacturing) so the knurling on the bearing would "interlock" with the corresponding grooves in the cap. Kind of like how a splined fitting works.
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Old 2012-06-25, 04:05 PM   #12
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"Anti-Slip" Solution

I decided to use a shim. But rather than cutting a piece of aluminum can, I used a piece of aluminum tape instead, and it worked great! It's has strong adhesive backing so it won't move once it's in place, but can also be removed easily if necessary.

And because it's fairly soft, the knurling on the bearing will "imbed" itself well into the aluminum strip, and therefore it should hold well. It took just one thin strip to basically match the thickness of the layer of powder coating that had been removed. I'll test it later today but I think it should be slip-free!

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Last edited by MuniAddict; 2012-06-25 at 04:13 PM.
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Old 2012-06-25, 05:16 PM   #13
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That dreaded bearing slip is why I stop riding my Schlumpf G26er off road( I don’t have the skill to gracefully dismount) . I now have the hub in a HK29 frame and it make a great uni to ride down the bike path to the local hill trail which I ride in low gear. Even on the bike path I once had to make a quick stop for some clueless biker that cut me off and I had the bearing slip.

If the aluminum tape works under high stress let us know. Also let me know if you would be willing to sell a strip.

Last edited by muddycycle; 2012-06-25 at 05:25 PM.
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Old 2012-06-25, 05:36 PM   #14
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Quote:
But rather than cutting a piece of aluminum can, I used a piece of aluminum tape instead, and it worked great! It's has strong adhesive backing so it won't move once it's in place, but can also be removed easily if necessary.
That's probably going to make it worse as the adhesive will become gooey when warm or wet, as well the foil is so thin that it won't add significant thickness.

Adding a layer between the bearing and cap/frame will double the number of surfaces, which will increase the liklihood of slippage. You'd be better off following Kris's advice and filing down the caps so you regain some clearance and hence the ability to properly tighten the bearings OR follow Eric's advice and bond the cap to the bearing.

Honestly, given the risks of slippage and the risk of overtightening, Eric's idea is clearly the best way to go; it also sounds like Schlumpf is heading that direction.

In terms of the permanency off such a bond, don't worry as there really is nothing that will bond permanently to metal, so a nice contact adhesive like weld wood or barge cement, even red loctite might work though I wonder how well it woudl bond over time if there is flex in the bearing-cap joint.
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Old 2012-06-25, 06:32 PM   #15
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As for my aluminum tape/shim idea, so far there are no issues, and in preliminary tests it's holding perfectly under massive back pressuring on descents, and down pressure on steep climbs. I took the cap off immediately after a hard back pressure stop, and it was cold as ice and the shim hadn't budged.

Kris told me he also had a couple bearing slips which he said had ground a substantial amount of material off the cap and frame, enlarging it to the point where he could no longer use it for schlumpf riding.

He still had slipping even after filing down the cap and frame interface. So the next option would be to fill that enlarged space back to original proportions. It's just a matter of which material is best for that, and so far the alum. tape is working just as expected.

If it does end up breaking down, I will probably go back to the more traditional aluminum can shim, and *bond* that to the inside of the caps.
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Last edited by MuniAddict; 2012-06-25 at 06:36 PM.
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