General Cycling Discussion - Snapped 7800 Durace cranks

Just wondering if anyone has any advice on what i should do about my Durace cranks which snapped clean off at the point where the axle meets the drive side spider. I'm an average 160 pound local A grade cyclist with a bit of kick but no sprint ace. They failed during full power and left me with serious bruises on my inner thigh. The local bike shop said they must have been crash damaged previously and not covered under warranty ! They have had enough milage to be due for a new big chain ring but that is it. Any help would be appreciated.

Maybe try contacting Shimano directly?

I've seen pcad post a pic of a broken DA crank, but I don't know if it was his set so maybe he or someone else that had the same problem can help you.

And welcome to the forums.

That bike shop "must have" is BS. With enough mileage and time aluminum will fatigue and fail if used by a strong rider who gets out of the saddle but it should not be in less time than to wear out a set of chainrings. Sounds to me like possibly a defective forging got through inspection.

Did you talk to the LBS owner and was it the shop that you purchased the bike from? If not then try it. If it was then I would let them know that they will never sell you another bike. A DA equipped bike is not a small sale for most LBSs.

Hey, thanks for those posts. The problem is they were bought second hand and were added to the bike later. My lbs is saying i should have bought them new and it would teach me for being so cheap ! I don't really have a leg to stand on by the looks of things. In a way it does go to show you that Durace isn't really bombproof after all.

Hey, thanks for those posts. The problem is they were bought second hand and were added to the bike later. My lbs is saying i should have bought them new and it would teach me for being so cheap ! I don't really have a leg to stand on by the looks of things. In a way it does go to show you that Durace isn't really bombproof after all.


Having been secondhand you don't know what they went through in their life before you. Secondhand, I wouldn't have pursued a warranty claim even. You roll the dice when you buy used.

-R

As I mentioned earlier ANY aluminum crankset used by a strong rider will eventually fail due to metal fatigue. I knew one rider who destroyed a C Record crankset too due to fatigue. Per my understanding aluminum cranksets used by professional teams are replaced regularly for just that reason. Not sure about replacement intervals they use however.

If you are a racer or hard riding athletic rider aluminum cranks should be considered a wear out item and replaced regularly. Could save your gonads, and possibly your frame, if you land hard on the top tube when a crank breaks.

Hey, thanks for those posts. The problem is they were bought second hand and were added to the bike later. My lbs is saying i should have bought them new and it would teach me for being so cheap ! I don't really have a leg to stand on by the looks of things. In a way it does go to show you that Durace isn't really bombproof after all.

Since you didn't buy them from the shop, I don't see how it can have any responsibility at all. Even Shimano may be blameless--I'd guess it was a faulty forging (I've seen others break, both Shimano and Campy), but nobody has any way of knowing what the previous owner did with or to them.
You're lucky to get away with bruises, btw. A friend of mine snapped a Campy crank a couple of years ago, broke two vertebrae and spent weeks in traction. It took almost a year of PT before he was able to walk and ride again.

Thanks again for all the postings that have been made. According to the instructions that came with the new set of Durace cranks i have fitted "before every ride the crank set should be inspected for any sign of wear and should be replaced if any damage is noted " I guess that covers their asses. But still, who is going to dismantle their crank set 4 or 5 times a week.. In my case the axle snapped just inside the right hand external cup making a quick check impossible. Tatfield had an interesting point though saying a crank set is a disposable item and requires regular replacement. So there you go..

It sounds like the spindle failed which was not clear to me from your original post. Is this a DA crankset with the spindle integral with one arm? When I wrote of aluminum fatigue I was thinking more of a crank arm failure due to fatigue. Except for Ti spindles that was the common failure mode on older forged aluminum cranksets with solid square taper spindles.

You are right about disassembly being a PITA as your failure point would not be visible w/o doing so. I would also think that repeated disassembly/reassembly to inspect that area would be as likely to cause problems than prevent them.

Contact Shimano about the failure and ship the parts to them to examine if they ask you to. A metallurgist there could determine the cause of failure probably. You might end up with a additional replacment crankset for free.