Chain won't stay on largest cog



Y

yk

Guest
I have a rear derailleur adjustment question. It is Shimano RSX, 7 speed.
I cannot keep the chain stay at the largest cog. It falls back to the 2nd
from largest unless I keep pressing the shifter. L limit screw setting
seems to be correct, because if I turn it 1/4 turn more, then the chain
jumps over the largest cog.. If I make the cable tighter by turning an
adjustment barrel, the chain won't shift down to the smallest cog. Is
there anything else I can try ? Could this be caused by a worn chain or a
gear ? TIA.
 
yk wrote:
> I have a rear derailleur adjustment question. It is Shimano RSX, 7 speed.
> I cannot keep the chain stay at the largest cog. It falls back to the 2nd
> from largest unless I keep pressing the shifter. L limit screw setting
> seems to be correct, because if I turn it 1/4 turn more, then the chain
> jumps over the largest cog.. If I make the cable tighter by turning an
> adjustment barrel, the chain won't shift down to the smallest cog. Is
> there anything else I can try ? Could this be caused by a worn chain or a
> gear ?


See if your changer is aligned in the vertical before you
have a long sad story like our 'changer in spokes'
concurrent thread poster.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971
 
Has it ever worked? Is the derailleur designed for the size of the largest
cog; is it an MTB cassette (28+ teeth) on a road derailleur (designed for
<27 teeth)?

Justin Vincent

--

"yk" <[email protected]> wrote in message
news:[email protected]...
>I have a rear derailleur adjustment question. It is Shimano RSX, 7 speed.
> I cannot keep the chain stay at the largest cog. It falls back to the 2nd
> from largest unless I keep pressing the shifter. L limit screw setting
> seems to be correct, because if I turn it 1/4 turn more, then the chain
> jumps over the largest cog.. If I make the cable tighter by turning an
> adjustment barrel, the chain won't shift down to the smallest cog. Is
> there anything else I can try ? Could this be caused by a worn chain or
> a
> gear ? TIA.
>
>
 
yk wrote:
> I have a rear derailleur adjustment question. It is Shimano RSX, 7 speed.
> I cannot keep the chain stay at the largest cog. It falls back to the 2nd
> from largest unless I keep pressing the shifter. L limit screw setting
> seems to be correct, because if I turn it 1/4 turn more, then the chain
> jumps over the largest cog.. If I make the cable tighter by turning an
> adjustment barrel, the chain won't shift down to the smallest cog. Is
> there anything else I can try ? Could this be caused by a worn chain or a
> gear ? TIA.
>
>


May be that you rear der is so 'over adjusted' that the first 'click' of
the lever, doesn't move the rear der to the next cog. Shift all the way
down, loosen the inner wire, screw the barrel adjuster almost all the
way down, pull the inner wire tight and reconnect. Then shift once, see
if the chain moves to the next cog, fine adjust, then shift up the cogset.
 
"Justin Vincent" <[email protected]> wrote in message
news:[email protected]...
> Has it ever worked? Is the derailleur designed for the size of the largest
> cog; is it an MTB cassette (28+ teeth) on a road derailleur (designed for
> <27 teeth)?
>
> Justin Vincent
>

You may be right ! It is a road bike with 26inch wheels. It is REI's
Novara Radonee. I don't know history of bike. I got it used. It has
Shimano RSX STI shifter. and both rear derailluer and rear wheel hub have
RSX mark. They are probably original. As you guessed, the largest cog has
28 teeth. Does it mean MTB cassette and not compatible with the derailluer
?
Thanks.
 
"Qui si parla Campagnolo" <[email protected]> wrote in message
news:1112019254.ede2092292056fbccaf725dd7832596a@teranews...
>
> May be that you rear der is so 'over adjusted' that the first 'click' of
> the lever, doesn't move the rear der to the next cog. Shift all the way
> down, loosen the inner wire, screw the barrel adjuster almost all the
> way down, pull the inner wire tight and reconnect. Then shift once, see
> if the chain moves to the next cog, fine adjust, then shift up the cogset.


I replaced the shift cable and follow the derailleur adjustment procedure
from scratch.
The problem is that the rear pulley does not line up with the largest cog
unless I keep holding the shifter.
There is a small offset that causes the chain to fall to the next cog.
 
On Mon, 28 Mar 2005 19:34:03 -0800, yk wrote:

>
> "Qui si parla Campagnolo" <[email protected]> wrote in message
> news:1112019254.ede2092292056fbccaf725dd7832596a@teranews...
>>
>> May be that you rear der is so 'over adjusted' that the first 'click' of
>> the lever, doesn't move the rear der to the next cog. Shift all the way
>> down, loosen the inner wire, screw the barrel adjuster almost all the
>> way down, pull the inner wire tight and reconnect. Then shift once, see
>> if the chain moves to the next cog, fine adjust, then shift up the cogset.

>
> I replaced the shift cable and follow the derailleur adjustment procedure
> from scratch.
> The problem is that the rear pulley does not line up with the largest cog
> unless I keep holding the shifter.
> There is a small offset that causes the chain to fall to the next cog.


There is a reasonable probability that your derailleur bracket is bent.
This will cause the problem you are having. There are tools to straighted
bent brackets. Check with a good local bike store.
 
"A Muzi" <[email protected]> wrote in message
news:[email protected]...
>
> See if your changer is aligned in the vertical before you
> have a long sad story like our 'changer in spokes'
> concurrent thread poster.
>


No matter what I do, a rear pulley won't lineup to the largest cog once I
release the shift lever.
 
<[email protected]> wrote in message
news:[email protected]...
> The Park Tool website (http://www.parktool.com/) has excellent,
> step-by-step instructions for adjusting index-shift systems.
>

Actually I follow this instruction step by step, but cannot make the pulley
line up to the largest cog.
The problem may be an incompatible cassette or damaged derailleur ?
 
On Tue, 29 Mar 2005 03:41:26 +0000, sg wrote:

>> The problem is that the rear pulley does not line up with the largest cog
>> unless I keep holding the shifter.
>> There is a small offset that causes the chain to fall to the next cog.

>
> There is a reasonable probability that your derailleur bracket is bent.
> This will cause the problem you are having. There are tools to straighted
> bent brackets. Check with a good local bike store.


This is a good guess, if all the other adjustments are correct. Starting
over with the adjustment from scratch should have cured any other trouble.
By the way, the tool to straighten the derailleur hanger is usually
called an adjustable wrench. Be very careful if your frame is aluminum.

--

David L. Johnson

__o | "A foolish consistency is the hobgoblin of little minds, adored
_`\(,_ | by little statesmen and philosophers and divines." --Ralph Waldo
(_)/ (_) | Emerson
 
On Mon, 28 Mar 2005 19:22:39 -0800, yk wrote:

>> Has it ever worked? Is the derailleur designed for the size of the largest
>> cog; is it an MTB cassette (28+ teeth) on a road derailleur (designed for
>> <27 teeth)?
>>
>> Justin Vincent
>>

> You may be right ! It is a road bike with 26inch wheels. It is REI's
> Novara Radonee. I don't know history of bike. I got it used. It has
> Shimano RSX STI shifter. and both rear derailluer and rear wheel hub have
> RSX mark. They are probably original. As you guessed, the largest cog has
> 28 teeth. Does it mean MTB cassette and not compatible with the derailluer
> ?


It's not that it is a mountain bike cassette that makes is problematical,
but the size of the big sprocket may be too big for the derailleur. This
casts doubt on the other diagnosis of a bent hanger.

Check to see that the hanger is straight, though. The pulleys should be
lined up below the cog -- when, say, you are in the middle of the cassette
and the middle chainring. Any misalignment between the jockey pulleys
could be a problem. It may be the hanger, or it may be a worn-out or
otherwise damaged derailleur.

But if it is only the largest cog that causes trouble, this may be the
answer. Try to adjust the "b" screw that controls the rotation around the
hanger; that may help as well.

--

David L. Johnson

__o | Accept risk. Accept responsibility. Put a lawyer out of
_`\(,_ | business.
(_)/ (_) |
 
yk wrote:
> <[email protected]> wrote in message
> news:[email protected]...
>
>>The Park Tool website (http://www.parktool.com/) has excellent,
>>step-by-step instructions for adjusting index-shift systems.
>>

>
> Actually I follow this instruction step by step, but cannot make the pulley
> line up to the largest cog.
> The problem may be an incompatible cassette or damaged derailleur ?
>
>


Time for a trip to see a competent bike wrench!!! Could be a lot of
things which, w/o seeing it, are hard to diagnose.
 
David L. Johnson wrote:
> On Tue, 29 Mar 2005 03:41:26 +0000, sg wrote:
>
>>> The problem is that the rear pulley does not line up with the
>>> largest cog unless I keep holding the shifter.
>>> There is a small offset that causes the chain to fall to the next
>>> cog.

>>
>> There is a reasonable probability that your derailleur bracket is
>> bent. This will cause the problem you are having. There are tools
>> to straighted bent brackets. Check with a good local bike store.

>
> This is a good guess, if all the other adjustments are correct.
> Starting over with the adjustment from scratch should have cured any
> other trouble. By the way, the tool to straighten the derailleur
> hanger is usually called an adjustable wrench. Be very careful if
> your frame is aluminum.


Ack! Use the Park-specific tool... using adjustable wrenches for a more
delicate operation like this one may lead to over-adjustment and subsequent
compensation, further aggravating the problem.
--
Phil, Squid-in-Training
 
"Phil, Squid-in-Training" <[email protected]> wrote in
message news:[email protected]...
> David L. Johnson wrote:
> > On Tue, 29 Mar 2005 03:41:26 +0000, sg wrote:
> >
> >>> The problem is that the rear pulley does not line up with the
> >>> largest cog unless I keep holding the shifter.
> >>> There is a small offset that causes the chain to fall to the next
> >>> cog.
> >>
> >> There is a reasonable probability that your derailleur bracket is
> >> bent. This will cause the problem you are having. There are tools
> >> to straighted bent brackets. Check with a good local bike store.

> >
> > This is a good guess, if all the other adjustments are correct.
> > Starting over with the adjustment from scratch should have cured any
> > other trouble. By the way, the tool to straighten the derailleur
> > hanger is usually called an adjustable wrench. Be very careful if
> > your frame is aluminum.

>
> Ack! Use the Park-specific tool... using adjustable wrenches for a more
> delicate operation like this one may lead to over-adjustment and

subsequent
> compensation, further aggravating the problem.
> --
> Phil, Squid-in-Training
>


I don't see any obvious damage or bend with the derailleur or hanger (a part
of frame), but, it may be different for an expert. By the way, it is a
steel frame. As many suggested, it is probably the best to leave it to a
pro. I have one more question though. It seems very difficult to find the
same derailleur (RSX). anymore. Can I use different model, such as
Shimano Sora without replacing the shifter ? TIA.
 
yk wrote:
> "Phil, Squid-in-Training" <[email protected]>
> wrote in message news:[email protected]...
>> David L. Johnson wrote:
>>> On Tue, 29 Mar 2005 03:41:26 +0000, sg wrote:
>>>
>>>>> The problem is that the rear pulley does not line up with the
>>>>> largest cog unless I keep holding the shifter.
>>>>> There is a small offset that causes the chain to fall to the next
>>>>> cog.
>>>>
>>>> There is a reasonable probability that your derailleur bracket is
>>>> bent. This will cause the problem you are having. There are tools
>>>> to straighted bent brackets. Check with a good local bike store.
>>>
>>> This is a good guess, if all the other adjustments are correct.
>>> Starting over with the adjustment from scratch should have cured any
>>> other trouble. By the way, the tool to straighten the derailleur
>>> hanger is usually called an adjustable wrench. Be very careful if
>>> your frame is aluminum.

>>
>> Ack! Use the Park-specific tool... using adjustable wrenches for a
>> more delicate operation like this one may lead to over-adjustment
>> and subsequent compensation, further aggravating the problem.
>> --
>> Phil, Squid-in-Training
>>

>
> I don't see any obvious damage or bend with the derailleur or hanger
> (a part of frame), but, it may be different for an expert. By the
> way, it is a steel frame. As many suggested, it is probably the
> best to leave it to a pro. I have one more question though. It
> seems very difficult to find the same derailleur (RSX). anymore.
> Can I use different model, such as Shimano Sora without replacing the
> shifter ? TIA.


Good thinking, and yes, you can use any Shimano derailleur without replacing
the shifter. Make sure you don't get one that's "RapidRise" also known as
"low-normal."

--
Phil, Squid-in-Training
 

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