MintSauce Posted March 19, 2018 Posted March 19, 2018 I've experienced at least 3x MTB rear derailleurs being destroyed on one of my bicycles in my life. In every instance, it was as a result of a foreign object being caught in the chain and/or derailleur. About 2 weeks ago I experienced a broken derailleur on my road bike for the first time.I left a downhill tar road at a fair pace, hit a slightly rough gravel road with a very steep incline, shifted into the easiest gear and 2 pedal strokes later... BOOM! It seems to me (I'd like to believe, seeing as I do my own maintenance) the limit screw is still in the correct position, so my riding buddy and I were both a little dumbstruck. Anyone have an opinion on what could've happened? Sent from my SM-G930F using Tapatalk
hagar Posted March 19, 2018 Posted March 19, 2018 about 2 years ago i also trashed my rear deraileur on my road bike it was my chain that caused the problem . A kink in my chain got stuck in the derailer
MintSauce Posted March 19, 2018 Author Posted March 19, 2018 cross chaining ? No, I had just shifted to the small chainring. I don't know if it's possibly just a combination of a number of things happening at the same time...drop from big to little chainring/shift from smaller to largest cog/hitting a bunch of gravel corrugations? Maybe the chain came of the lower pulley wheel due to the bumps and somehow got caught between the cage and spokes? Who knows?!
David Marshall Posted March 19, 2018 Posted March 19, 2018 Possibly chain suck on the small chain ring. Usually from wear and often in combination with wear and dirt. The chain sticks to the small ring until it jams under itself at the top of the ring and then rips the derailleur or hanger off. Usually after you have fitted a new chain.
Capricorn Posted March 19, 2018 Posted March 19, 2018 where's the top pulley wheel? ripped out or unscrewed? got pics of that or was it a roadside donation? How long is your chain? Keep it clean? what do you clean it and the drivetrain with? What do you lube your chain with? I ask because it seems the paint seems to be flaking off, and the exposed metal is corroded on portions of your rear mech that should be effectively protected from most of the elements. So somehow, the paint is either being scraped off, or there's some chemical paint removing going on. Chemical degradation of metal can occur, especially portions with stress raisers (like machined grooves/threads), that when given an unusual loading, can result in fracture.
MintSauce Posted March 22, 2018 Author Posted March 22, 2018 Possibly chain suck on the small chain ring. Usually from wear and often in combination with wear and dirt. The chain sticks to the small ring until it jams under itself at the top of the ring and then rips the derailleur or hanger off. Usually after you have fitted a new chain. No sign of chainsuck on the frame. The derailleur left clear damage on the frame, just above the dropout on the rear of the seat stay as well as a slightly bent spoke where it got caught.
MintSauce Posted March 22, 2018 Author Posted March 22, 2018 where's the top pulley wheel? ripped out or unscrewed? got pics of that or was it a roadside donation? How long is your chain? Keep it clean? what do you clean it and the drivetrain with? What do you lube your chain with? I ask because it seems the paint seems to be flaking off, and the exposed metal is corroded on portions of your rear mech that should be effectively protected from most of the elements. So somehow, the paint is either being scraped off, or there's some chemical paint removing going on. Chemical degradation of metal can occur, especially portions with stress raisers (like machined grooves/threads), that when given an unusual loading, can result in fracture. The top pulley was nowhere to be found. Got pulled out of the cage. The chain was not sparkling clean, but not particularly dirty. I recently started lubing with Smoove, although I don't love it as it seems to gunk up the chain too much. Chain length was spot on. The chain is close to needing replacement and a new one is going on today, but chainwear tool shows it still has some life in it. No twists in the chain either. I refitted it with the new derailler and it has been fine. I don't clean with any sort of chemicals. Bike gets ewashed with soapy water. I do an annual complete strip and then remove chain, chainrings and derailleur pulleys and clean seperately with a degreaser. Never anything but mild soap and water on frame and components. I also noticed with interest the corrosion. That bothers me quite a bit. I mean, I know I live in Cape town, but that shouldn't happen. The reason the paint flaked off is because that particular part of the derailleur is bent through almost 90 degrees. I have no doubt whatsoever that the reason the derailleur broke is because it ended up in the spokes, as per the damage on the frame and the bent spoke.
droo Posted March 22, 2018 Posted March 22, 2018 May have been a stone getting caught between the cage and the spokes? Unlucky, but possible. Either that or there's a sneaky engineer somewhere at Shimano that programmed a random self destruct sequence in to the DI2 system. The only RD I've ever had do that to me was because of a stick that got caught between the chain and chainstay and pulled the chain all the way back up to the seatstay...
Mongoose! Posted March 22, 2018 Posted March 22, 2018 ....snip...... broken derailleur on my road bike for the first time.I left a downhill tar road at a fair pace, hit a slightly rough gravel road with a very steep incline..., snip ......... Gravel road on a road bike nee man
MintSauce Posted March 22, 2018 Author Posted March 22, 2018 Gravel road on a road bike nee man What? Mine does the occasional singletrack mission too. In fact, on Mondays CPT/Hout Bay/Kalk Bay mission we would've done the greenbelt if we had anything left in the legs.
MintSauce Posted March 22, 2018 Author Posted March 22, 2018 May have been a stone getting caught between the cage and the spokes? Unlucky, but possible. Either that or there's a sneaky engineer somewhere at Shimano that programmed a random self destruct sequence in to the DI2 system. The only RD I've ever had do that to me was because of a stick that got caught between the chain and chainstay and pulled the chain all the way back up to the seatstay... Same here, there's always clear evidence of what caused it. Your dodgy Shimano engineer theory seems most likely at the moment
V12man Posted March 22, 2018 Posted March 22, 2018 The top pulley was nowhere to be found. Got pulled out of the cage. The chain was not sparkling clean, but not particularly dirty. I recently started lubing with Smoove, although I don't love it as it seems to gunk up the chain too much. Chain length was spot on. The chain is close to needing replacement and a new one is going on today, but chainwear tool shows it still has some life in it. No twists in the chain either. I refitted it with the new derailler and it has been fine. I don't clean with any sort of chemicals. Bike gets ewashed with soapy water. I do an annual complete strip and then remove chain, chainrings and derailleur pulleys and clean seperately with a degreaser. Never anything but mild soap and water on frame and components. I also noticed with interest the corrosion. That bothers me quite a bit. I mean, I know I live in Cape town, but that shouldn't happen. The reason the paint flaked off is because that particular part of the derailleur is bent through almost 90 degrees. I have no doubt whatsoever that the reason the derailleur broke is because it ended up in the spokes, as per the damage on the frame and the bent spoke.Top pulley fell out first? got jammed and into the spokes it goes....
Mongoose! Posted March 23, 2018 Posted March 23, 2018 https://www.bikehub.co.za/classifieds/298958-shimano-ultegra-di2-rear-derailleur/
MintSauce Posted March 24, 2018 Author Posted March 24, 2018 https://www.bikehub.co.za/classifieds/298958-shimano-ultegra-di2-rear-derailleur/Thank you for the tip off, but I also dislike scratches :-) Just so happens my brother was placing an order from CRC the day this happened. Landed an R8050 for about R2800 a week later. Sent from my SM-G930F using Tapatalk
'Dale Posted March 24, 2018 Posted March 24, 2018 I also yanked my SRAM Red derailleur punching up a small kicker I reckon dirty or somewhat gritty drivetrain caused that...
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