Broken Front Mech

My front mech (derailleur) broke when I rode out to meet Shaun C. for this ride on Wednesday so I had to do the rest of the ride on a single chainring.

Since then I have bought a new front mech and have been able to work out what went wrong by comparing the new mech. to the old one. Here is a picture of the broken derailleur:

Broken front mech.
Broken front mech.

(The red circle highlights where the metal snapped.)

I’ve been having problems with my front shifting for about a year now, but I’d put it down to a worn chain and chainrings. What didn’t occur to me, however, was that the shifting didn’t improve this summer when I put new chain and chainrings on the bike! I’d just got used to struggling with the changes and had stopped worrying about them, despite the fact that the bike used to change chainrings quite happily a few years ago.

The groupset on the Basso is 10 years old now. (I originally had it on my Bianchi, but that frame eventually got scrapped after a crack developed in it due to damage caused by airport baggage mis-handlers.) The reality is now clear – the front mech was worn out. I’d had a very simplistic view of how the front mech. works – I thought it just shoved the chain off for changes to smaller rings, and jammed the chain against bigger rings for up-shifts, relying on the chainring to ‘pick up’ the chain.

When the up-shifting got worse, I simply over-pressed the shift lever to increase the friction between chain and ring until something happened. More often than not, this resulted in the chain going straight over the big ring and ending up wrapped round the right crank. I became expert at slowing my cadence, shifting the mech. back slightly and riding the chain back onto the big ring in one fluid motion. Both a clever and a stupid trick!

I should have sorted the problem out a year ago but I’d got it into my head that front derailleurs have such an easy job to do that there isn’t much that can go wrong with them, short of actually breaking, as this one did in fact. The reality is now clear though – the new derailleur has sculpted channels on its inner surfaces. These channels are no doubt carefully designed to guide the chain on its way during the front shifts. When I look at the broken mech., I can see where such channels used to be, but 10 years of hard work have worn them away so that the inner plates are now almost smooth. That mech. could no longer do anything other than shove the chain about. It certainly couldn’t help gently lift or drop the chain. I’d had to use brute force to make my front shifts and this unwanted stress was bending the derailleur cage each time. Eventually, the metal fatigued and broke along a very clean line.

Post Mortem verdict: A negligent approach to maintenance meant that the worn out derailleur was not replaced when it should have been. This meant that excessive force had to be used to initiate gear changes. Eventually, this led to failure.

Recommendations: Clean and inspect bike regularly and make any adjustments necessary for safe, reliable operation. Replace worn parts before they become unreliable or unsafe. Especially – never ignore strange noises from the bike – they mean something, and it probably isn’t something good! 😉

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4 Responses to “Broken Front Mech”

  1. That is the sort of thing that happens to me, I am terrible with bike maintainance!

  2. Oh, I forgot to mention…

    When I was out with Shaun, I noticed that my front brake blocks were almost worn down so I’ve just replaced them. I neglected to do that on my first MTB once, trying to get just one more ride out of the blocks. They wore out on a fast dangerous descent and I destroyed my front wheel braking metal-on-metal!

  3. I’ve never broke a front mech, i’m great at breaking everything else though. .

    I’ve snapped loads of cranks,
    The springs always go in my rear mechs or I manage to put them into my rear wheel.
    The ratchets always fail on my shifters
    The springs go on my brake calipers.
    The bearings go in everything.

  4. I’ve snapped one crank.

    My mate put his rear mech into his wheel when I was out with him once. He destroyed the mech, broke several spokes, mangled the chain and snapped his gear hanger off. He had to borrow my bike to ride back to his car while I guarded the wreck of his bike.

    I wore the entire ‘transmission’ out on my MTB by leaving a chain on too long. It’s much cheaper to change chains more frequently!

    I’ve pitted the cups and cones on the Campag Proton rear wheel of my Cannondale by not noticing that the locknuts had come loose and riding a couple of hundred miles like that.

    If I had the money, I’d put my bikes in to my LBS a couple of times a year for servicing.

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