Bicycle rear gears - sudden failure

[GeorgeB]

'Light, strong, cheap. Pick any two' is a popular saying.

Factor in the trade off between strength/hardness and ductility/brittleness and it (hopefully) should be clear that lifespan is a different thing altogether i.e. These lightweight expensive components you don't understand...

I think I understand composite materials a bit better now. I was out cycling this afternoon on a three year old road bike which I've used for several hundred miles but has never been altered, crashed or mistreated.

All of a sudden, with no warning, the CAMPAGNOLO Xenon 9 speed rear mech just snapped off. The first I knew about it was a sudden jamming of the transmission as the rear mech went into the spokes. I was on a cycle path and and did not fall off the bike but it could have been much worse. I just looked up this component. It comes from a leading supplier and is about £30 - so hopefully not 'cheap junk'. And yet it seems this component is not fit for purpose and should never have been used by the bicycle builder. I'm sure my arc welded forks and glued handlebars would last longer than the composites which they have used in this gear changer. Here's a photo of the broken component:

 

[the snooper]

i can feel a george repair job coming on glue / fibreglass or something completely different go on george suprise us

 

[breezer]

Campag stuff is normally spot on. surprising.

 

[Barney1973]

Am a keen cyclist myself and take part in cross country races and ride trails around the country,my bikes take alot of abuse and components such as bottom brackets,cables,brake pads etc wear on a regular basis but I have never had a rear mech fail but have seen it happen but only in extremely muddy conditions.I don't buy high end mechs usually shimano SLX which is an entry level mech that costs about £35 so I think you have been very unlucky with your mech breaking,how old is your chain as this can cause problems due to it stretching over time?

 

[R Kraft]

The plastic looks like it has an amazing amount of porosity.
Robert

 

[brightspark]

the component looks like swiss cheese or an aero bar not suprised its happened. its not rocket science to see the weakness with the blow holes

 

[wyn]

By the look of it i first thought you had set fire to the plastic....That does look like a very poor bit of plastic moulding.

 

[GeorgeB]

Thank you for your comments. I read that another model of theirs was composite but, looking at it, perhaps mine is made of plastic. Either way, I agree the bubbles look like a serious manufacturing defect. There's no way I'm going to attempt to glue that back together! I'll take it to the large store who sold me the bike and ask for a replacement component. The bike is a few years' old and definitely outside warranty but I understand a product can still be deemed not fit for purpose (faulty) if it fails when you wouldn't reasonably expect it to. There's also a heath and safety issue but I'll be amazed if the shop accepts my claim, and it might not be easy to pursue any claim.

 

[spartan]

Why not try on one of the cycle forums, you might not be the only rider with this problem. With more ammo you might have more chance of getting some joy from the shop

 

[Barney1973]

Heres some theories from a bike forum,does happen but is pretty rare as far as i can tell
http://forum.ctc.org.uk/viewtopic.php?f=5&t=36569

 

[GeorgeB]

Heres some theories from a bike forum,does happen but is pretty rare as far as i can tell
http://forum.ctc.org.uk/viewtopic.php?f=5&t=36569

Wow, that was a good find - so recent and similar, too. Thanks also to spartan for the forum suggestion. I must sign-up and add my photo. I don't think the chain jammed in my case. I was in some middle gear, just coasting along when it happened. In any event, the component looks poorly made.

When I get a replacement rear mech, I'll have to make sure it's made of metal, rather than plastic. I'm shocked to find that Campagnolo used plastic for a structural element like that.

 

[Mr Mike]

George your better off just going out and buying a new mech the Xenon range from campag is the cheapest stuff they do. The chances of you getting a replacment mech slim to non, unless you willing to take campag to court over a £30 mech. By the look of your mech I would guess your limit screws are not set properly, the lower jocky wheel is twisted inward meaning the mech was still attached when it court the wheel, the mech would of then extended untill the main linkage pivots over loaded snapping between them and the dropout bolt. I would also look at the true of your rear wheel and the conditon of the gear hanger, before you go shouting at your local bike shop coz you might need a wheel true and a gear service to the the bike right

 

[hotrodder]

Rear derailleur and it's mounting to the frame are subjected to little in the way of stress i.e. one of the jobs for the rear mech is to lightly tension the slack portion of the chain. Forced/bad gear changes, jammed chains/freewheels, badly set up gears etc obviously alter the picture...

I was in some middle gear, just coasting along when it happened

Something must have jammed for it to snap (defective part or not) as there's zero stress (well, ok gravity) on the chain and rear mech when coasting/freewheeling.

Xenon is/was the entry level Campag kit i.e. not proper cheap tat but the cheapest kit they produce. Back when i was commuting 30 miles a day + weekend rides i doubt i'd get a year out of a similar quality part before all the pivots were sloppy etc

I understand a product can still be deemed not fit for purpose (faulty) if it fails when you wouldn't reasonably expect it to

As usual it's more complicated than that- initially it's down to the manufacturer to proove that the part wasn't faulty but at some point (and sometimes still within warrenty period!) the roles are reversed and it would be up to you to proove that part wasn't intentially abused/broken/dropped or otherwise not fit for purpose

 

[GeorgeB]

George your better off just going out and buying a new mech the Xenon range from campag is the cheapest stuff they do.

You make some interesting observations. I have no idea if you're right about the limit screws. I thought everything was set up OK.

What alternative 9-speed product would you suggest? Can I fit models to a road bike if they are described as being for a mountain bike?

hotrodder - any claim I make would be based on the Aero appearance of the plastic - that surely can't be right and seemed destined to fail.

 

[superls]

i had this exact thing happen to my 18 month old mountain bike, trashed the wheel and the chain. cost me a small fortune to replace it all.

 

[Shox Dr]

To follow on from what Hotrodder was saying.

This IS a common breakage IF.

You are trying or are running in a crossed gear, ie Big at the front big at the rear. If the limit screws are not set correctly, but more importantly chain length, if the chain is too short for Big-Big running it over stretches the rear mec, causing this breakage. It has happen to me and others I know. Before I learnt

Note; Rear mecs, (and front ones for that matter) will last longer and change gear better if you remember the following.

Do not cross the block (rear set)
So if in the smallest at the front only use the top half of the rear cassette
In the biggest at the front only use the lower half at the rear.

In the middle at the front it is OK to use the full cassette.

Always make sure the limit screws are set correctly, as a combination of this a worn/tight chain, and crossing over and moving to a bigger gear at the rear (easier to pedal) WILL pull the mec into the spokes, causing the problem you had.


I don't hold out much hope for a free replacement. useless you moan like an old git

 

[GeorgeB]

Note; Rear mecs, (and front ones for that matter) will last longer and change gear better if you remember the following.

I'm well impressed with the level of knowledge and help here. What a good forum this is! Many thanks.

I was cruising along in the middle of three gears at the front (like I use 95% of the time) and some middle-ish gear at the rear. It wasn't a hill and neither was I in top gear to 'go faster'. The chain is the correct size. All the parts are original. I agree the chain could have worn a bit but EVEN IF the chain jumped the gears or something, this rear mech should be manufactured to a level which supports crash-type trauma. You wouldn't expect to see a trailing arm for car suspension made of carbon fibre. I don't think they even allow you to weld parts like that. I just noticed that this rear mech is made of composite, rather than plastic. If it was carbon fibre, they'd shout it from the roof tops and put the price up so I doubt if it is carbon fibre. Therefore, what is it? It reinforces my opinion that the vacuum process and air extraction failed during manufacture.

 

[tigler]

Composite just means a composition of more than one material. The fibre part in this case could be anything.
GRP, glass fibre reinforced plastic, for example, is a composite of chopped strand glass fibres in a plastic resin.
Carbon fibre, on it's own, is useless. It must be woven and held in a resin for it to provide it's famous qualities.
So, the fibre composite in that mech could be anything. However, I would imagine that Campag would have done accelerated age and endurance testing to determine adequate life from the chosen material. Great as long as they also allow for abuse, and any overstressing which plastic doesn't like.
Personally, I've never been a fan of plastic in structural applications. In my experience it always eventually fails from fatigue or decomposition, when it does repair is typically impossible, and if the part is by that time obsolete and unavailable the whole piece of equipment is rendered scrap.
Bad enough on a passive item, but potentially dangerous in this case.

 

[Shox Dr]

They are NOT crash proof. In fact they will break very easily. I've lent a bike up against a wall and the bloody mec has broken. And that was a XTR mec



Reminds me I really ought to post in "what's you job" or in my case what was your job.

 

[GeorgeB]

Composite just means a composition of more than one material. The fibre part in this case could be anything.

There's little sign of any fibre in this component by Campagnolo. Perhaps they forgot to add it to the mix for my batch. The material reminds me of insulation type foam which surrounds copper water tanks (immersion heaters) for example. Chunks of the foam just snap off when put under the slightest stress. Here's a better photo of the side which remained attached to the bicycle frame.