Broken Campy sprocket...

[kramnnim]

So today I stood up to sprint the last few hundred feet from the top of a local climb, and suddenly had that horrible feeling of "I'm pedaling but not moving forward!"

At first I thought the freehub pawls failed (which makes no sense considering there are 4 of them), but soon found that my chain was riding on nothing but spacers.

http://i.imgur.com/EDnyxSE.png

Ended up removing one spacer, and replaced it with a lid ring (?) from a Gatorade bottle. Tightened the lockring with a screwdriver as best I could, and rode 90 miles home without major problems.

Has anyone seen this happen before? The cassette isn't especially old, and I was only applying 700w when it broke.

[Lionel]

was the lockring torqued to spec ?

[regularguy412]

I've only known of a cog broken during an event, once in my cycling career. It happened during a 40K State TT event and it was a long time ago. The guy who broke it was a sprinter who would normally win the Cat I / II title. His dad was following in a car and swapped his wheel. I have no idea if it was Campy or Shimano,, as I did not personally 'see' the wheel/cog in question, but it was certainly the talk of those present during the post-event medal presentations.

Note: This was on a dead-flat course with no more than 3 feet of elevation gain/loss.

Mike in AR:beer:

[Louis]

was the lockring torqued to spec ?

I was wondering the same thing. (I assume you mean before the incident, not for the repaired configuration.)

First I wondered how the lock ring could possibly be removed while out on the road, then it occurred to me that if the cog came off that would cause the stack of cogs to loose tension, and the lock ring might be more easily turned.

[kramnnim]

I don't have the correct socket (crows foot?) to grab hold of the lockring tool...need to procure one. Always used a big adjustable wrench.

Based on feel, I think it would be close to the 40nm/29.5 foot pounds. Obviously my arm is not calibrated at all....heh.

And yes, the lockring was loose once the sprocket was gone.

[Scooper]

Has anyone seen this happen before? The cassette isn't especially old, and I was only applying 700w when it broke.

Yes. The same thing happened to a riding buddy. He was climbing out of the saddle when it happened. Lickton's replaced the whole cassette under warranty, and the failed cog went to Campagnolo for analysis.

http://i32.photobucket.com/albums/d7/k4drd/Bicycles/1994%20Paramount%20540ALWA94012/CIMG6900sm.jpg

http://i32.photobucket.com/albums/d7/k4drd/Bicycles/1994%20Paramount%20540ALWA94012/CIMG6902sm.jpg

[YoKev]

Nice MacGyver skills!

[FlashUNC]

Had a friend snap a SRAM rear cog like that.

[Tony T]

Always used a big adjustable wrench.

Based on feel, I think it would be close to the 40nm/29.5 foot pounds. Obviously my arm is not calibrated at all....heh.

Looks like we might have found the cause of the cog failure.....

[Pegoready]

Wow, replacing the spacer with a Gatorade bottle ring and riding another 90 miles?! Amazing.

[kramnnim]

Looks like we might have found the cause of the cog failure.....

How many people actually use a torque wrench on lockrings? There should be hundreds of broken sprockets out there if it is that crucial... But if it is, was my lockring too tight or too loose?

http://blog.artscyclery.com/tag/cassette-lockring-torque/

[FlashUNC]

I've certainly felt like I was snapping into pieces like that at the top of Pilot.

[Lionel]

How many people actually use a torque wrench on lockrings? There should be hundreds of broken sprockets out there if it is that crucial... But if it is, was my lockring too tight or too loose?

http://blog.artscyclery.com/tag/cassette-lockring-torque/

Way too loose if you could remove it without the tool.

[nrs5000]

I did this once to a 14t campagnolo cog, standing up to carry speed into the base of a climb.

[Tony T]

How many people actually use a torque wrench on lockrings? There should be hundreds of broken sprockets out there if it is that crucial... But if it is, was my lockring too tight or too loose?


Too tight. If you own a torque wrench (and why wouldn't you), why not use it?
(BTW, I torque everything from water bottle bolts to, yes, the lockring).

[Ralph]

I use a TQ wrench on about everything also....including the lock ring. However.....I do not believe the lock ring is very sensitive to being over tightened. But if it's too loose, and allows the cog to wobble under load, that's not good.

[Salsa_Lover]

Was also an spacer broken?

I guess the most probable thing was that with the overtorque a plastic spacer could have broke leaving the cogs loose which could lead to a broken cog.

[dogdriver]

Jeez. Now I'm feeling like a dolt. I just tighten the lock ring until it clicks a few times after feeling resistance.... and I do own a torque wrench.

[kramnnim]

Way too loose if you could remove it without the tool.

The lockring was loose once the sprocket broke out. Which I already said. :)

[kramnnim]

Too tight. If you own a torque wrench (and why wouldn't you), why not use it?
(BTW, I torque everything from water bottle bolts to, yes, the lockring).

As stated previously, I don't have a massive socket to connect the torque wrench to the lockring tool. (yet)

I don't see how being too tight would affect the metal sprocket before the plastic spacers would deform. And no, none of the spacers were broken.

[ultraman6970]

1st time I see this problem, incredible and must suck big time trying to get back home with what ever gear is working.

[pbarry]

As stated previously, I don't have a massive socket to connect the torque wrench to the lockring tool. (yet)

I don't see how being too tight would affect the metal sprocket before the plastic spacers would deform. And no, none of the spacers were broken.

You don't need a 1/2" drive ratchet for the cassette tool. A 3/8" to 1/2" adapter will do the job just as well.

If you bought the cassette from a U.S. retailer, pursuing a warranty replacement might prove rewarding.

[kramnnim]

You don't need a 1/2" drive ratchet for the cassette tool. A 3/8" to 1/2" adapter will do the job just as well.

If you bought the cassette from a U.S. retailer, pursuing a warranty replacement might prove rewarding.

It's the socket I do not have. My Pedros tool doesn't have a 1/2" square drive, you need to use a...22mm (?) socket to fit over it.

Got the cassette from a forum member, so no warranty claims possible... Not a big deal, I just robbed one from a cassette I had retired. (teeth on the larger sprockets were getting a bit sharktoothy)

[cfox]

Too tight. If you own a torque wrench (and why wouldn't you), why not use it?
(BTW, I torque everything from water bottle bolts to, yes, the lockring).

if you are tightening bottle bolts with a torque wrench, you are likely over tightening them. No consumer available torque wrench is accurate below 3 nm, certainly not one that goes to 40nm to tighten a cassette lock ring (I know, I'm sure you own a big one and a little one like me). I do use the honker torquer on the cassette, but for bottle bolts, finger tight with a L-shaped allen key is plenty. I agree it's important to use a torque wrench on the casette, but I know good mechanics that just haul down on it with a big crescent wrench and call it a day.

[pbarry]

It's the socket I do not have. My Pedros tool doesn't have a 1/2" square drive, you need to use a...22mm (?) socket to fit over it.

Got it. The Crescent should work fine. "Tight enough" on the cassette should be the torque you'd use to firmly snug, but not finally tighten, lug nuts on an alloy car wheel. If that advice contains too much gray area for some, just look away, and think pleasant thoughts..

The OP made it home after this failure using his wits and ingenuity. No doubt about his mechanical aptitude and mechanic's feel. :)

[Tony T]

As stated previously, I don't have a massive socket to connect the torque wrench to the lockring tool. (yet)


Just get the Spindoctor Lockring tool (http://www.performancebike.com/bikes/Product_10052_10551_1030394_-1___000000).
It accepts a 1/2" socket drive:

http://media.performancebike.com/images/performance/products/200/40-3770-NCL-TOP.jpg


If your torque wrench is a 3/8 inch drive, just use a 3/8" to 1/2" adaptor (http://www.amazon.com/TEKTON-1770-Ratchet-Adapter-3-Piece/dp/B000NPT5JO/ref=sr_1_3?s=hi&ie=UTF8&qid=1377478611&sr=1-3&keywords=socket+adapter)

[choke]

It's the socket I do not have. My Pedros tool doesn't have a 1/2" square drive, you need to use a...22mm (?) socket to fit over it. A socket in whatever size you need shouldn't be too expensive. FWIW, the Campagnolo tool takes a 24mm.

[Chief]

It appears to me that this was either a 14t or 15t cog that failed and that there is a missing piece. Correct? Shown is failed 14t cog for which I have no details as to how it occurred. I think it is a Scram cog, but I may be mistaken. Note that there is also a missing piece here. I'll bet that if you look carefully that the failure initiated where there was a stamping on the cog. I don't believe that over tightening or for that matter under tightening is the cause of the failure. Failure is due to a stress concentration produced by the imprint of the stamp. Note that the cracks that you see in this photo are post failure cracks; i.e., they occurred after the missing piece departed from the cog.

[kramnnim]

Yep, 15t...and yes, one of the breaks is at the stamped ramp. No clue if it was the first place to break, though. And yes, there's a missing piece...probably still on the road. The three I picked up were spread out a bit.

There's no way I overtorqued the lockring by anything significant- the alloy lockrings feel way too flimsy. It was probably within 5 foot pounds of spec. If undertorque is the cause, I shouldn't have made it home...without the tool I was only able to get it 3-4 clicks past fingernail tight. Maybe 1 foot pound...lol.

[Louis]

As I think someone said above, it's unlikely that this failure was due to over-torquing the cassette lock ring.

[merlincustom1]

Too tight. If you own a torque wrench (and why wouldn't you), why not use it?
(BTW, I torque everything from water bottle bolts to, yes, the lockring).

T, I thought the lockring spec was 50nM? I could be wrong.

[kramnnim]

Depends on the lockring...mine say 40nm.

[rice rocket]

Buy Shimano cassettes. Problem solved. :)

Good thing they just went 11 speed too, right?

[oliver1850]

Looks like one too many lightening holes in the cog to me (the one right below the ramp).

I doubt very much the failure was related to LR torque. My guess would be unfortunate timing of shifts, putting side load on the cog at just the wrong point. Would probably have to happen multiple times.

Most LR tools (Park) have a 1" hex. If you have a 3/8" torque wrench, this socket will let you eliminate LR torque from the next cog failure question.

http://www.ebay.com/itm/Performance-Tool-W38032-Chrome-Socket-3-8-Drive-1-6-Point-Shallow-/190889918390?pt=Motors_Automotive_Tools&hash=item2c71ecffb6&vxp=mtr#ht_1762wt_1213

Regardless of whether you think you have a claim: I'd send it to Campagnolo just so they could see it. If they see multiples with the same failure, they will improve the part.

[Tony T]

T, I thought the lockring spec was 50nM? I could be wrong.

Campy Chorus is 40nm

[Tony T]

As I think someone said above, it's unlikely that this failure was due to over-torquing the cassette lock ring.

Maybe yes, maybe no, as we have no idea of what the cassette was torqued to.
However, as the OP said that none of the plastic spacers were cracked, I would tend to agree with you.

[Hank Scorpio]

I broke a 14 tooth record or chorus cog too. Why is it in such a limited sampling that we have 4 broken 14t of two different manufacturers? I accounted mine to being in the wrong gear when making a slight effort on a flat to a short hill burst.