I broke something but I don't know what???
 

I was out riding Kanuga Trail in Paris Mtn. State Park here in Taylors, SC when I heard a loud pop. As a super-Clyde I am hard on parts. Let me explain and see if you can diagnose the problem.

I was in the easiest speed on the bike (1-1; smallest in front, biggest in rear) because I was going up a really steep technical section at very slow speeds. In one particularly steep and difficult section, I stood up to pedal and that is when I heard the popping noise. At first I thought I broke my chain again, but when I got off to look at it, the chain was fine (it is fairly new). Also, my RD hanger is perfectly aligned and I could not ask for a more perfect chain alignment.

So, next, I checked my chain rings and cassette for broken or damaged prongs or deformations. Once again, everything looks brand new in the front and rear. I walked the bike up the steep technical section because I am not skilled enough to start on something that steep. Then I got back on the bike and noticed that my bike didn't like to coast. When the back wheel spins during coasting, it wants to turn the cassette as well, instead of spinning freely. In addition, at the next little hill I went up it popped again and basically won't let me put any high load on it.

The shifter still works fine (aligned etc) and this problem happens in any gear combination. The bike is not changing gears when it pops.

Here is my guess, but I have zero experience: The rear free hub ratchet mechanism is shot. That is the only thing I can think of. The crank set is perfect. The chain is perfect. The RD is perfect. The cassette is perfect. Everything is aligned. I think it's the free hub ratchet mechanism.

Anybody have this problem?? The bike is only 1 month old--Gary Fisher Piranha.

Thank you!

I think your diagnosis is correct!
A 2nd guess would be a broken axle, but you can check that easily by just taking the wheel off the bike.

Yup, agree wit the ratchet thingy. I had a bud that his new Madone did jsut about the same thing. I told him what I thought it was. He couldn't stop pedaling or the chain would pop off with the continued motion of the pedals. The rear derailleur would bobble around.

He took it to the shop. They tried to seel him a new chain, cassette and all other sorts of stuff. In the end, it was the ratchet sytem. He ended up getting lots of stuff for free since they felt bad for the misdiagnostic exam!:D

I too believe you got the right diagnostic, broken freewheel or snapped axel.

Sorry to hear about your poor GF, it should be under warranty so get that bike to the O.R. (LBS) stat. <<<--Sorry bout that, Mrs. Bautieri had Grey's Anatomy on TV last night.

When inspecting the cassette, I take it you checked there's nothing jammed in there that binds the cassette with the rest of the wheel?

I'm asking this because a couple of weeks ago someone *cough* forgot to fasten the bungee chord on my rear rack. One of the hooks ended up wedged between largest rear cog and hub/spokes. I could not get the hook out with multitool pliers, had to cut the bungee instead and leave the hook there. On the way home I rode what I guess could be called a geared fixie. Weird ride. Back home, I removed the cassette and got the hook out without any further complications.

--J

You probably broke the pawls in the freehub. It's not an item that breaks often nor easily. I also wouldn't expect it to break on a 1 month old bike. Take it back to the shop and have them look at it. It should be a warranty issue.

Below is a cut away of a freewheel (you have a freehub) but the principle is the same. Pointer #2 is what broke on your bike.

http://i32.photobucket.com/albums/d7...eelCutaway.jpg

My buddy's Madone was only 4 months old. Not top of the line wheels but you'd expect that this shouldn't happen on a 3k+ bike, but stuff happens!:(

BTW, thanks for the diagram. I know the symptoms but never seen one taken apart or the actual part.

Thanks for all the responses. Here is an update:

I took the bike to the LBS today and the guy said that it was just cable stretching! I asked him point blank if that would cause the cassette to move when I spun the rear wheel in a forward direction. He said yes! Okay, first of all, cables do not stretch. The shifters and RD can get worn in, thus seeming like the cable stretched, but steel cables simply do not stretch. Second, I don't care if you bend the RD at a 90 degree angle, the cassette should not spin when you spin the wheel in a forward direction. He lubed everything up and said that he was certain it was just the cable. Hmmmm.... I'm going to go ride the bike again, and if it's not fixed (which I'm quite certain it isn't) I'm taking the bike right back the the shop and asking for gas for my wasted trip!

Edit: Oh yeah, and all the people at the LBS said that this guy is the best. I've been riding for a little over a month, and I think I would be better at diagnostics than he is.

That guy sucks! Samething my bud went thru. 4 or 5 trips before they pulled their heads out. Always makes me wonder, a dip like me can see what's wrong but they can't. I think it's more like they don't want to see it! Might mean they have to work to solve the problem.:mad:

My bud was lucky, he got to keep the stuff they were planning to charge him for, chain and cogset after it didn't solve the problem. Of course I told him I wouldn't pay for their stupidity!:thumb:

That doesn't mean squat! The guy that transefered my components from one frame to another was the best too! He installed all the bolts dry. A bearing race in the headset upside down (annoying tick). I bought a new front derailleur cause he told me it wasn't shifting properly. Turns out he installed a kinked cable (which new cables were part of the package).
I found the incorrect bearing race myself, lubed all the bolts he didn't.

Worst thing was that I tipped him $30 for the $50 service he did. If I had known!:mad:

okay, blow the guy off since you know more than him.

Cables do stretch. The steel inner cable does elongate some. But what is more critical is the outer housing compresses. That's why they say to make fine adjustments using the barrel adjusters every few miles when new (usually around 100 miles of riding and evry 100 after than for a few times)

Okay, here is the update on the bike.

First of all, to StanSeven, I realize now that really I am arguing a moot point in regard to the cable stretch deal. Regardless of what is happening, the end result is the same--cable tension is decreased. The real point of my argument had to do with the LBS mechanic not knowing that the cassette should not spin when the rear wheel does (when spinning forwards). He specifically said that a cable tension problem would cause that problem---uh...no. And by the way, as an Engineering grad and soon to be science teacher, I pulled out my books and did some calculations.

Hooke's Law applies in the elastic region of a material (before the proportional limit of the material). Most cable manufacturers use standard stainless steel for their cables for which to reach the proportional limit you would need to apply around 60,000 pounds of force per square inch to reach--in other words, we are no where near the proportional limit, so Hooke's Law applies. Using the standard Young's modulus for steel, E=20(10^3) ksi, Hooke's Law tells us that in order to make a standard 1.2 mm cable strain (elongate) merely one width of an average human hair (1/1000 of an inch) one must apply 4,304 pounds of force to that cable. To put things in perspective, strongman Mark Felix, the current GNC Grip Gauntlet world record holder, did a one-handed dead-lift grip of 301 pounds. If he were to grip a brake lever at the end where there is somewhere around a 10:1 mechanical advantage and squeeze with all his might, the cable would experience approximately 3010 pounds of force and would not even stretch the width of an average human hair. Keep in mind that most people cannot squeeze near that hard, and if they did, the brake levers would break.

Conclusion, say whatever you want about settling in, shifting, or housing compression, but those steel cables experience macroscopically undetectable elongation. Like I said, it is a moot point because the effect is the same, but I was not going to let you have the last say. Please holler if you find my math is critically flawed.

Okay, about the bike. I took it out today (finally), and ,surprise, surprise, the same problem on the same hill! Only this time, much worse. The cassette is permenently affixed to the hub now, so I had to walk down the long downhill stretch at the end (it was either that or take the chain off and I was too lazy to take it off). Hmmm.... I'll take the bike in tomorrow and see if he'll have any mercy on me because of his misdiagnosis.

I once thought I knew more than the head mechanic at the local shop. Boy was I sorry! My wheel (I built) has lasted over 17000 miles and the one he built didn't even make thur the first 40 mile ride! Silly me, what was I thinking?:D

Once you mentioned the cable, my first thought was that you can remove al the cale, manually shift the rer der and it still shouldn't hang up as you describe. How could it be the cables?:rolleyes:

You might try running another wheel as a test.

Not sure if you math is right, the usual issue with cables is that a new cable has housings at each housing end is a metal end cap, which fits into a cable holder in the frame, when one uses the brakes or shifter this puts compression on this combination, forcing a compressing of the fit, which appears to make the cable lengthen or stretch. As for your bike, my guess is the hub ratchet mechanism is pooched.

To be fair to the mechanic though, it was probably wishful thinking, not wanting to have to rebuild the wheel on a new hub.....

That's funny, when my bud's wheel turned out to be faulty, it was replaced by Trek, the mfg'er ,not the shopdude. Sounds like the shopguy just doesn't want to take the time to look into the warranty issue. Clean the cable and say, "ok it's done".

Either that or he's scared he'll lose money in someway. But c'mon, he wants the customer to lose money by paying for something that should be in working order and isn't? She the customer take the loss instead?:eek:

I am beginning to agree with both of you (mechanic just lazy, not that dumb). I got the bike back, and it's fixed under warantee. It was the "freehub body."

Yeah, to make it clear, I do not disagree that something which looks like cable stretch occurs, but the steel cable itself is not elongating. Here is another proof of that. If the cable itself were to stretch, the cable would continue to stretch approximately linearly for the life of the cable, not just during the first month. Stretching during the first month only proves that the actual cable is not elongating.

Keep in mind that the cables are twisted-strand. And so even if there is not sufficient force involved to elongate any one of those individual strands, there certainly is sufficient force to get all those strands to "mate" together more tightly. So, yes they do stretch. And depending on the brand, it can be quite a bit.

Jgedwa is exactly right. Just looked up some data from Dynatek on 4.8mm stainless cable (bigger than bike cable). That cable would stretch 4.25 feet per 1000 feet of cable with 1000 pounds of force on it. So, significantly reduce the force and length and diameter, and you're left with still a pretty small amount--nonetheless, significant. I'll eat my words...cables do stretch, but not because the steel is stretching, but because the twisted cables do some sweet morph action. Thanks for pointing that out jgedwa.

One note, the original post was referring to shifting, and the rules there are different then they are for braking, which is why housing used for dérailleur cables is not recommended for brake applications. Dérailleur cables see a very limited amount of actual force, since the only force placed on it by shifting is enough to overcome the spring in the dérailleur trying to shift it to the home position, if you grab the two connecting points of a dérailleur with your hand you can easily overcome that spring, it is enough to cause the cable to seat in though.

Brakes need to clamp the shoes to the rim or disk, and that force needs to be considerably higher, but it's still pretty minimal, I can apply the brakes on my mountain bike with 2 fingers, now there is some leverage in the lever, but still, I doubt that it would be sufficient enough to cause much cable deformation if any. And any deformation in a brake cable is probably hidden in brake shoe wear.

That wheel should be a warranty item. I had a Race Lite wheel with a loose bearing and they replaced it no questions asked. Got my replacement in 2 days. Bontrager wheels have a 5 year warranty.

Certainly your engineering coursework must have shown you the folly in applying linear theory to real-world applications?

Bikes experience a phenomenon called "cable stretch". It's called that because it's not steel elongation and "cable stretch with housing compression and seating" is much too long to say.

Told ya:rolleyes: But you knew that any way.

Bikes are pretty simple mechanisms and when stuff goes wrong, it's pretty easy to figure it out. Go over to Park Tools and start studying. You'll be fixing your own stuff in no time;) I've known lots of engineers that can be trained to do simple tasks. Complicated ones too, if you give them enough treats:D

Ha, yeah, I need to go buy some of the bike specific tools, and I'm sure I could do much of my own work, as anybody else could.

Dude, come on! There are 2 absolutes in the world.
1 - Cables DO NOT stretch.
2 - You CAN NOT train an engineer to do simple tasks(at least - not simply)! :roflmao2:

I know that bears are easier to train but you can train engineers if you use the right treats;) Give 'em a new gadget and you can get them to ride bicycles:D