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 Post subject: Ouch! Why?
PostPosted: Mon Aug 10, 2020 9:54 pm 
Retro Guru

Joined: Sat Apr 15, 2017 12:26 pm
Posts: 718
Location: Lost now on the country miles
If you don't like the sight of blood, don't look any further. First the 'Ouch!' then the 'Why?'.
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Knuckles: ouch! Shoulder: ouch! Cuts, grazes, blood, bruises . . . Face vs gravel incident: very ouch! :facepalm:

Fortunately, not at high speed - probably only 11-12mph. But why?

As far as I can make out, this happened: on a 3 x 8, I was cruising along in 3 and 6; I went over a few little bumps and the chain jumped from sprocket 6 to jammed between sprocket 8 and the dropout. Derailleur hanger is not bent; limit screws are fine; indexing is fine. As far as I can tell the chain just bounced and jammed the wheel. Fortunately, I wasn't going 30mph and I wasn't on a road. However, I don't want to repeat the experience. Anyone got any ideas why this happened? Rear mech set up as in the photo below:
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 Post subject: Re:
PostPosted: Mon Aug 10, 2020 10:03 pm 
Retro Guru

Joined: Sat Oct 25, 2008 12:17 am
Posts: 1669
Location: Chesterfield
Surely if chainset jammed as you describe the bike would just freewheel ?


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 Post subject: Re:
PostPosted: Mon Aug 10, 2020 10:11 pm 
Old School Hero

Joined: Fri Jun 14, 2013 6:03 pm
Posts: 246
I would say you need a new chain as yours looks tired to say the least , I had a similar thing happen on my old Dawes that I only use for the canal towpaths, it would jump gears suddenly esp under load . New chain and no problems at all now...worth a try.


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 Post subject: Re: Re:
PostPosted: Mon Aug 10, 2020 10:51 pm 
Retro Guru

Joined: Sat Apr 15, 2017 12:26 pm
Posts: 718
Location: Lost now on the country miles
d8mok wrote:
Surely if chainset jammed as you describe the bike would just freewheel ?

Yes. Good point. Perhaps I ought to think again about this when the concussion has gone.

The chain is only a couple of months old and has done less than 300 miles. However, I recently put an old cassette on to try some different ratios and the 6 to 7 changing has been a bit odd.


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 Post subject: Re: Ouch! Why?
PostPosted: Mon Aug 10, 2020 11:13 pm 
Old School GrandMaster | Rider
Old School GrandMaster | Rider
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Joined: Thu Nov 26, 2015 7:29 pm
Posts: 7379
Location: peak district
Chains do jump about, some people remove links to keep the chain tensioned more or fit a device like a DCD.


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 Post subject: Re:
PostPosted: Tue Aug 11, 2020 8:14 pm 
Retro Guru

Joined: Sat Apr 15, 2017 12:26 pm
Posts: 718
Location: Lost now on the country miles
Yes. I've been wondering about this today and, on reflection and less dazed, I think that what must have happened is that the chain bounced (this is my springiest bike), got wedged between the cassette and dropout, which stopped the chain rings dead and my pedalling efforts and momentum sent me over. Either that or I've lost the ability to ride over bumps the size of moderately heaped dinner plates. :facepalm: The concern is that it could have happened somewhere where the consequences would have been much worse, e.g. right next to a five ft drop to a stony beach. I don't want my cycling to suffer the same fate as Martyn Ashton's.

Unfortunately, the only clutch mech I can find that would be compatible with my 90s Gripshift is by SunRace and unavailable anywhere. I've never had a DCD but I've been investigating and I gather that they did work pretty well: good call. I can feel a bit of shopping coming on.


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 Post subject: Re: Ouch! Why?
PostPosted: Tue Aug 11, 2020 8:20 pm 
Old School Grand Master

Joined: Tue Oct 09, 2007 1:55 pm
Posts: 10260
Location: New Forest, UK
I had a similar sort of thing last year, BANG and I was on the deck on the mildest of curves.

I never worked out why, I think I hit a stone (the size of a tomato perhaps?) which went directly under the front wheel rather than popped out sideways. As a result the front wheel lost grip and down I went.

The odd thing is that the front tyre never ran true again so something appears to have damaged its carcass..invisibly.


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 Post subject: Re:
PostPosted: Sat Aug 29, 2020 4:00 pm 
retrobike rider
retrobike rider
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Joined: Fri Aug 08, 2008 2:36 pm
Posts: 18747
Location: Yorkshire, England
Honestly the reason why it happened is you are riding the working bike. You need a Gravel bike to ride on gravel.

In the real world, back in the day up until people though they were pointless and more importantly look stupid, there where spoke guards, it stop this chain between the spokes nonsense (P.S. check the spokes, there may be bends and large gauges on them now, but that why the wheel stops fast as it pulls it around.).

Clean it up, ignore clutch mechs, look at some less worn gear and maybe a stronger spring rear mech or less worn jokey wheels(something else to check...) etc.
Oh because stuff happens unfortunately.

If it happens a lot, then something is wrong.


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 Post subject: Re:
PostPosted: Sun Aug 30, 2020 10:23 am 
Retro Guru

Joined: Sat Apr 15, 2017 12:26 pm
Posts: 718
Location: Lost now on the country miles
Like Hamster, I don't think I'll ever be sure what happened. The chain was off at the drop out end of the cassette, not the spokes end of the cassette, though. Whether that was a cause or consequence of the crash, I don't know. However, I cannot think of another reason for going over the top of the bars. If I had been taking chances and crashed I would accept it; the disturbing thing was that this was safe riding and it still happened - fortunately, not in traffic or at the edge of a precipice. Whatever, that bike is getting a brand new rear mech of one type or another before I go out on it again.

"If it happens a lot, then something is wrong." If it happens a lot, the dental bill will be enormous! :D


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 Post subject: Re:
PostPosted: Sun Aug 30, 2020 11:12 am 
Retro Guru
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Joined: Tue May 11, 2010 6:39 pm
Posts: 1725
Location: South Devon
CassidyAce wrote:
The chain was off at the drop out end of the cassette, not the spokes end of the cassette, though. Whether that was a cause or consequence of the crash, I don't know. However, I cannot think of another reason for going over the top of the bars. If I had been taking chances and crashed I would accept it; the disturbing thing was that this was safe riding and it still happened - fortunately, not in traffic or at the edge of a precipice. Whatever, that bike is getting a brand new rear mech of one type or another before I go out on it again.


You have my sympathies. I came off fairly recently (my own fault) and I don't want it to happen again soon.

When I came off I think part of the reason was possibly that I had got a bit of lube on the back tyre. Add a wet cattlegrid into the mix, and bam. I'm normally obsessive about maintenance and things being perfect. That time I thought I'd get away with it! Never again. Ironic perhaps that I'd just replaced the chain and cassette due to a scary chain slipping moment...

Most people ensure their bike is safe to ride by buying new or taking it to a mechanic. That's not always a guarantee, but as Retrobikers we ride old bikes and they can have issues. Pretty much every "good condition" old bike I've ever bought has had safety critical issues - sometimes I've discovered these in the stand, or sometimes on the trail. When it's out riding it can cause a scary moment. Jumping gears or odd shifting are a sign that something is not quite right so really it's best to sort these issues as soon as you can.

These days when I buy an old bike I always err on the side of caution. That tends to mean a full strip and rebuild before any serious riding. Intermittent drivetrain faults can be a pig to diagnose but I generally find that starting again and checking everything solves it. I don't use old cassettes unless I know their history, and chainrings get binned at the first sign they are misbehaving.

Even with all this care things need a decent shakedown. If you're running a mix of modern and old components you can have weird issues too.

Anyway as I say, sorry about the off. You've reminded me that my Giant has a chain suck problem when changing down to the smallest front ring, which sometimes means the chain jams. I think it's probably because it ideally needs a longer cage mech, but perhaps something to do with worn chainrings. It can take a while to fully diagnose and shake down these sorts of problems.

Whatever the problem is this bike only gets used for relatively gentle stuff at the moment! I was thinking about taking it for a ride today, but perhaps I'll fit a different mech first... :roll:


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