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From: AMuzi <am@yellowjersey.org>
Newsgroups: rec.bicycles.tech
Subject: Re: Had a wtf? this morning - Ping AMuzi
Date: Sun, 23 Feb 2025 09:28:41 -0600
Organization: Yellow Jersey, Ltd.
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On 2/23/2025 5:12 AM, Shadow wrote:
> On 22 Feb 2025 22:21:58 GMT, Roger Merriman <roger@sarlet.com> wrote:
> 
>> Shadow <Sh@dow.br> wrote:
>>> Went out for my morning ride. Just before a rather steep hill changed
>>> down and I heard a clump and the chain jammed.
>>>
>>> I looked back and half of my rear derailleur was sitting on the
>>> asphalt.
>>>
>>> OMG, I thought to myself, this is almost as embarrassing as a crank
>>> arm falling off. Then faced the "walk of shame" home.
>>>
>>> Note, I scrub chain/jockey wheels/sprockets with water and detergent
>>> every 200 Km. Was almost due for a new clean. Gear change was
>>> absolutely smooth until the incident. HI and LOW screws perfect, no
>>> way the chain came off and "fell into the spokes".
>>>
>>> Note I managed to rip a spoke clear out of the wheel with the
>>> breakage. What fell into the spokes was half the derailleur. I suppose
>>> that'll mean a new wheel too
>>>
>>> 	:(
>>>
>>> <https://www.sendspace.com/filegroup/v/qdHDWfYEJvo99L3/MhFp6hhZL5Z8ugxHfSuN/uTo4>
>>>
>>> The "cleaned" in the filename is because I cleaned the EXIF metadata,
>>> not the parts after the incident....
>>>
>>> So "wtf" happened, what did I do wrong and how can I prevent it from
>>> happening again?
>>>
>>> TIA
>>
>> Did the derailleur come apart due to impact with wheel/cassette or a
>> failure and then do so?
>>
>> My old commute bike, had a rear mech fail where the cage and parallel meet
>> apparently was glued in place? Was an Alivio so broadly similar to the
>> Tourney I think from memory, Cues which I replaced it with is substantially
>> more heavily built like the MTB mech’s as to if it will last any longer?
>>
>> The Alivio lasted 9 years and 19,000 miles so probably got my moneys worth!
>>
>> Mind talking of Andrew I expressed surprise that front mech’s could wear
>> though! My Gravel bike front mech (Sora) had to be replaced due to that!
>> Only just shy of 12,000 and 7ish years old so definitely sub par, though
>> have replaced like with like and didn’t really seem any reason to match the
>> rest of the bike ie GRX mostly with Tiagra shifters.
>>
>> Okay (at least in uk) neither of Tourney/Alivio/Sora/Cues are particularly
>> expensive being £30ish for a derailleur.
>>
>> Roger Merriman
> 
> 	Thanks for the reply. The gear had around 8000 Km on it, and I
> replaced the jockey wheels last year the cogs were looking like spikes
> they were so worn.
> 	I have no idea what caused the breakage. There was a lot of
> debris on the road, but I was only doing around 15Km/h, possible but
> not likely I managed to pick up a twig and it flew into the spokes.
> 	It felt like it just decided to break..... I would have
> expected it to show some signs of failure beforehand.
> 	The bike has 8 gears at the back. The derailleur that broke
> was a RD-TX35, designed for 7 gears. Maybe that forced it.
> 	I can get a Shimano Tourney TY300 cheap, around US$ 15, or an
> Altus RD-M310L for around US$ 35. (since salaries, pensions etc in
> Brasil are roughly 1/10 of British, multiply by 10 to get an idea of
> relative prices).
> 
> 	PS I have no idea if it's short, long, over under etc. I have
> the only Shimano gear in town. Nothing to compare it to. People here
> use "Sunrun" and "Yamada" which sell for around US$ 4.
> 	[]'s
> 	
> 	
Those Shimano prices are comparable to US rates:

https://www.amazon.com/Shimano-Tourney-TY300-Derailleur-Standard/dp/B01K5C6F1U?tag=bngsmtphsnus-20&linkCode=df0&hvadid=80264466539886&hvnetw=s&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4583863993594891&psc=1

not much over currently lowest price sources here.

https://cambriabike.com/products/shimano-tourney-ty300-6-7-spd-mtb-rear-derailleur?variant=41153396179126&utm_source=bing&utm_medium=cpc&utm_campaign=PLA&scid=scbplpGM061319-31&sc_intid=GM061319-31


Given that it was well used, could well have been just 
overall wear.  You set the low gear limit back when it was 
less worn, but now all the pins and pivots are sloppy. Only 
takes a couple of millimeters more travel to go from normal 
clearance to engaged on a spoke.

-- 
Andrew Muzi
am@yellowjersey.org
Open every day since 1 April, 1971