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Chain slipped from second smallest cogs smallest under tension,to adjust B scew ?

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Chain slipped from second smallest cogs smallest under tension,to adjust B scew ?

Old 08-26-17, 06:38 AM
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Chain slipped from second smallest cogs smallest under tension,to adjust B scew ?

Hallo,
for several times recently, I stood on the bike when pedaling, then I felt the chain suddently droped,
it sounded like dropping from second to the smallest, but I did not really see it, however, I checked the alignment when chain sets on smallest cog, the chain and pulley and derailleur is strictly in line, you can see it in the photos, and I checked the schifting, it is perfect and smooth, so why the tension caused by my weight could trigger a chain sudden drop, should I adjust the B screw, assuming the distacne between the largest cog and up pully is too large or what? however, I did not find a B screw actually on this derailluer, it is a sachs huret 6 speed, indexed lever shifter for rear derailleur.

Thanks a lot!
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Old 08-26-17, 06:58 AM
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The B screw is there to stop the chain fouling the LARGEST cog, not really relevant with the smallest cogs. If the chain and cogs aren't worn, you're looking at either the adjustment being out or maybe a sticky cable making you think the thing's adjusted when it isn't.
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Old 08-26-17, 07:30 AM
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Attached is a 3000. It has a B adjustment screw. As you have surmised and looking at your pictures your 2000 does not appear to have one. In terms of the top jockey clearing the largest cog on the rear, that's what the B adjustment does, things look OK. However your jockey wheels appear to be worn.

I have no idea as to how that might affect shifting. I also wonder what is happening with your largest cog. It appears to be missing a chunk. No doubt it is some sort of special shifting helping mechanism but it looks a bit extreme.

Are your shifters friction or indexed and how many rings do you have up front? Given a possible 1990 for the bike if it is indexed then things might possibly not be adjusted properly. If it is friction then you live with poor shifting until your memory gets in tune with how far to move the levers.

Otherwise things look a bit old/messy or worn out. I would be tempted to remove the rear dérailleur. Take it to bits, clean it, fit some new jockey wheels with new grease and work the same into any springs. I would guess that you have a free wheel rather than a free hub. Six gears and no bulge in the wheel hub itself. Consider getting yourself a new free wheel as well.

As per europa same sort of thing and yes also look at your cables, inners and outers. They also look like they have spent quite a bit of time on the bike. Could be time to replace them as well... and the chain.

I guess basically I am saying I have no idea but if I were to buy your bike the first thing I would do as a matter of course is completely strip it down and start fitting new bits including most of the aforementioned.
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Old 08-26-17, 07:48 AM
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I think that you're looking at the wrong end of the bike. What kind of shifter do you have?
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Old 08-26-17, 08:04 AM
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jockey wheels look fine, arent they?

Originally Posted by chorlton View Post
Attached is a 3000. It has a B adjustment screw. As you have surmised and looking at your pictures your 2000 does not appear to have one. In terms of the top jockey clearing the largest cog on the rear, that's what the B adjustment does, things look OK. However your jockey wheels appear to be worn.

I have no idea as to how that might affect shifting. I also wonder what is happening with your largest cog. It appears to be missing a chunk. No doubt it is some sort of special shifting helping mechanism but it looks a bit extreme.

Are your shifters friction or indexed and how many rings do you have up front? Given a possible 1990 for the bike if it is indexed then things might possibly not be adjusted properly. If it is friction then you live with poor shifting until your memory gets in tune with how far to move the levers.

Otherwise things look a bit old/messy or worn out. I would be tempted to remove the rear dérailleur. Take it to bits, clean it, fit some new jockey wheels with new grease and work the same into any springs. I would guess that you have a free wheel rather than a free hub. Six gears and no bulge in the wheel hub itself. Consider getting yourself a new free wheel as well.

As per europa same sort of thing and yes also look at your cables, inners and outers. They also look like they have spent quite a bit of time on the bike. Could be time to replace them as well... and the chain.

I guess basically I am saying I have no idea but if I were to buy your bike the first thing I would do as a matter of course is completely strip it down and start fitting new bits including most of the aforementioned.
they just look fine, not very sharp at the end like a typical worn one.
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Old 08-26-17, 08:17 AM
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indexed lever , original from sachs huret

Originally Posted by Retro Grouch View Post
I think that you're looking at the wrong end of the bike. What kind of shifter do you have?
does this angle gives better details of the jockey wheels?
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Old 08-26-17, 08:56 AM
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Originally Posted by retro grouch View Post
i think that you're looking at the wrong end of the bike. What kind of shifter do you have?
+1
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Old 08-26-17, 09:48 AM
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I would first try indexing shifter, I think you have rear shifter cable set too tight. By the looks of your photos, there is a barrel adjustment, you can start here.

Could be lots of things but highly doubtful it's the B-screw,
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Old 08-26-17, 01:48 PM
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First you need to determine that the chain is actually dropping from the 2nd smallest cog to the smallest, rather than "skipping" when you apply high pedal pressure when on the smallest, which means that cog is worn. If it is dropping it is NOT the B tension screw, which affects only shifting onto a cog, not staying on it, and neither is it the limit screw. The most likely cause is cable/housing friction, as the derailleur cannot shift to the small cog unless the shifter is in that position. What you are likely experiencing is a delayed shift to the small cog. Putting pressure on the pedals would flex the frame enough to induce the cable to move the rest of the way.
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Old 08-26-17, 02:07 PM
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you hit the spot and I suspect lubing the cable housing is necessary

Originally Posted by cny-bikeman View Post
First you need to determine that the chain is actually dropping from the 2nd smallest cog to the smallest, rather than "skipping" when you apply high pedal pressure when on the smallest, which means that cog is worn. If it is dropping it is NOT the B tension screw, which affects only shifting onto a cog, not staying on it, and neither is it the limit screw. The most likely cause is cable/housing friction, as the derailleur cannot shift to the small cog unless the shifter is in that position. What you are likely experiencing is a delayed shift to the small cog. Putting pressure on the pedals would flex the frame enough to induce the cable to move the rest of the way.
also another comments points to the cable housing is set too high at the barrel adjust. gonna check it out. Thanks!!!
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Old 08-26-17, 02:11 PM
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Originally Posted by theunartist View Post
I would first try indexing shifter, I think you have rear shifter cable set too tight. By the looks of your photos, there is a barrel adjustment, you can start here.

Could be lots of things but highly doubtful it's the B-screw,
I think that derailleur design precedes index shifting. That's why I was curious as to what kind of shifter PO is using.
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Old 08-26-17, 02:41 PM
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Originally Posted by Retro Grouch View Post
I think that derailleur design precedes index shifting. That's why I was curious as to what kind of shifter PO is using.
Yeah!!! I think the OP has a lever tension shifter and not an index shifter.

I think the OP either has wrong cable tension or that adjustment screw on the lever itself is too loose when chain is under pressure.
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Old 08-26-17, 02:42 PM
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the yellow cable is holden in position to straighten the cable angle to adjust barrel

Originally Posted by europa View Post
The B screw is there to stop the chain fouling the LARGEST cog, not really relevant with the smallest cogs. If the chain and cogs aren't worn, you're looking at either the adjustment being out or maybe a sticky cable making you think the thing's adjusted when it isn't.
tonight will test it out to see if this solved the false shifting caused by cable housing distortion.
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