Intermittent "freewheel" for KH/Schlumpf hub

[osmundo]

I was cruising down a hill near my house in second gear tonight on my 36er Guni, just getting to some serious pace when the hub suddenly pops into this freewheel. I caught one step before I tucked into a roll on my hip and elbow, then sliding on my back. No serious injury but I chewed up the skin and muscle in those three areas.

The bigger concern is what to do about it. I have had my guni since the summer of 2008 and this has never happened. I keep it greased and it has been a very consistent performer for years. As soon as I picked up the uni after bouncing down the street it was back in gear and it seemed to shift fine.

This happened before when I first purchased the uni more than three years ago, but it always seemed to be in the process of shifting, never when I was cruising at speed in second gear. It eventually just stopped and it hasn't happened again in over three years.

The seems strange as well because the hub was under relatively little stress when the misfire occurred.

I'd love to hear comments from people about this. Any ideas for addressing the misfire besides dismantling a brand new wheel build, (I just had it completely rebuilt) and mailing the hub to Switzerland? It seems to work fine now but I sure am skittish about getting on and gearing up...especially downhill in traffic as I often do.

It is amazing how much trust we put in this equipment not to do precisely this.
(By the way, I did spend some time searching GUNI SHIFTING PROBLEM ect.. but feel free to point me toward a thread if I missed something.)

thanks

[tholub]

Check to see that your cranks are tight and installed correctly; a loose crank can creep out on the axle and press the button out far enough to go into neutral.

[saskatchewanian]

Are the buttons adjusted far enough out? (you can still push them in a bit when shifted)

Maybe the knurled bearing slipped in the holder?

That is about all I can think of besides what tom is suggesting.

[Klaas Bil]

Since you write you just had it completely rebuilt, you must also have reinstalled everything recently. That probably has to do something with the present mishap. My number one guess is what Satch wrote already: a button not adjusted far enough out. Check your installation manual on the details. Crank creep (as suggested by Tom) would be my second guess: it could move the button out of the position where the gears are securely engaged. I would think it's not the infamous bearing slip since the hub was under relatively little stress.

If it's any of these three, it would make no sense sending the hub to Switzerland because you would "destroy" the evidence (and in a way, fix the problem) when building the hub out of the uni.

Possibility number four is that you unknowingly touched the low-gear button. With old design hubs, this might cause the hub to freewheel. The newer hubs should either stay in high or switch to low, not be stuck in between gears. However, if you suddenly switch to low gear, it might feel as freewheel for a short while.

Let us know if you find out more.

[Tucson Uni]

I have experienced inadvertent downshifts on my 24 guni.

[brycer1968]

As described in the above posts, if your wheel builder wasn't intimately familiar with this type of hub its possible that the shift buttons or sloppy crank installation could be the source of trouble. After you rule those things out, another thing to check:

"You just had the wheel rebuilt"

So who built your wheel for you??

I do recall something in the product specs for my geared hub (#359) that said and I don't recall the exact language, something like: "if the spoke tension is too high, it could distort the hub and cause bearing problems". not sure if this could be the source of the problem you experienced, but I'd at least go to your wheel builder and ask him/her to check the spoke tension with a spoke tension meter and make sure they are all about the same even tension all the way around the hub and make sure that the tension isn't higher than is recommended for 14g straight gauge spokes (or what ever spoke you used). My park spoke tension meter came with a chart to id the range of tension for different spoke types. When I built my Schlumpf 29er, I finished the wheel build in the exact middle of this range of acceptable tensions for the type of spoke I was using and all the spokes were at almost exactly the same reading.

An educated guess: the sort of sutuation that would cause your hub to "distort" under improper tension is more likely to be uneven tension where a couple or a larger group of spokes were left way too tight on one side pulls the hub out of round - and might cause a malfunction???

Its worth checking it out.

Brycer

[corbin]

Slipping in high gear is usually the knurled bearing not being tight enough.

Also, it could be cause by excessively tight cranks (like way too high a torque value), and having the crank deform and get really close on the hub. But that is less likely. It is probably the first thing.

corbin

[tholub]

Originally Posted by corbin

Slipping in high gear is usually the knurled bearing not being tight enough.

Also, it could be cause by excessively tight cranks (like way too high a torque value), and having the crank deform and get really close on the hub. But that is less likely. It is probably the first thing.

corbin

Oh yes, I should have mentioned that; definitely a common issue, especially if you hear a grinding noise when it freewheels. Although usually if it freewheels because the bearing holder isn't tight enough, you can't just hop back on and ride it in high gear; it'll just slip until you tighten the holder.

[osmundo]

I appreciate all the feedback. I probably have 100 or miles on this wheel build without an issue prior to the big fall. It was built by the this guy that everyone in Denver metro pointed to when I made the rounds looking for someone to do it. It seemed like a competent job... I will have the tension checked. Great idea.

I'm not sure why the button position would make a difference, but that that also seems fine. I remember initially I had a ton of problems getting the crank arms not too tight, just tight enough and i ended up resorting to locktight, at Corbin's recommendation. I am going to re-install the crank arms as well

It just seems to different than the issues this hub had before. The neutral thing always seemed to happen when I was shifting, not cruising at high speed going down hill. I did not hit the button or put any particular tension on the hub...it just failed out of the blue...leaving me crumpled and bleeding on the pavement.

I am not too eager to see if it is going to happen again.

[siafirede]

Yeah, that sounds odd. I would be sure to check your frame bolts and crank bolts first. The buttons wouldn't matter unless you did hit them slightly on the way down.

Otherwise, take it easy and ride high gear on some slight downhills with pads and a helmet and make sure you test it under pressure and spinning fast before you go down something like Lookout Mountain again!

[corbin]

Originally Posted by osmundo

I appreciate all the feedback. I probably have 100 or miles on this wheel build without an issue prior to the big fall. It was built by the this guy that everyone in Denver metro pointed to when I made the rounds looking for someone to do it. It seemed like a competent job... I will have the tension checked. Great idea.

I'm not sure why the button position would make a difference, but that that also seems fine. I remember initially I had a ton of problems getting the crank arms not too tight, just tight enough and i ended up resorting to locktight, at Corbin's recommendation. I am going to re-install the crank arms as well

It just seems to different than the issues this hub had before. The neutral thing always seemed to happen when I was shifting, not cruising at high speed going down hill. I did not hit the button or put any particular tension on the hub...it just failed out of the blue...leaving me crumpled and bleeding on the pavement.

I am not too eager to see if it is going to happen again.

That really sounds like the knurled bearing slipping in the housing. The first time it happened to me I thought the hub was bad! Turns out it just needed to be tightened and I was good to go.

I still use blue lock tight on my main crank bolts; they never come loose anymore, and I never retighten them. I think I use about 30 or 35 ftlbs of torque.

corbin

[naturequack]

Osmundo,
Check out this thread.
http://www.unicyclist.com/forums/showthread.php?t=84211

I'm not sure how much this applies to your situation, but you never know. Got any circlips on that hub?

Geoff