Strange shifting problem

Josh Hassol said:

I recently re-cabled my rear derailleur. I adjusted the indexing and
got it working perfectly on the work stand. But when I'm out riding,
the derailleur will, from time to time, spontaneously shift to the next
smaller cog. This is not a case of BB flex causing ghost shifting. It
occurs under normal, easy pedaling, and I'm riding one of those older
Cannondale frames with the huge down tube (very stiff).

Each time the problem has occurred, I've stopped and tightened the
cable tension a little bit with the adjuster at the derailleur. It
seems to help each time but then, an hour or a day later, the same
thing happens. The chain is not "stretched," and I'm running all
Shimano stuff: Dura Ace shifters, Dura Ace chain, Ultegra cassette, 600
cranks, 105 short-cage derailleur. Nothing is worn, and it's all
clean and lubed. I've never had this problem before, despite having
re-cabled the bike a few times.

Ideas, suggestions?

First, the obvious: is the pinch bolt tight enough? It sounds like the
cable is being pulled out of place very slowly. Also, if you're using a
coated cable, did you remove the coating under the pinch bolt?

Then the non-obvious: how long has it been since you inspected the
housing? If one of the housing ferrules has failed, it could "shorten"
the housing by letting the wires poke through. If the housing is more
than a year or two old, replacing it would be a good idea.

Jeff

JeffWills said:

Josh Hassol said:

I recently re-cabled my rear derailleur. I adjusted the indexing and
got it working perfectly on the work stand. But when I'm out riding,
the derailleur will, from time to time, spontaneously shift to the next
smaller cog. This is not a case of BB flex causing ghost shifting. It
occurs under normal, easy pedaling, and I'm riding one of those older
Cannondale frames with the huge down tube (very stiff).

Each time the problem has occurred, I've stopped and tightened the
cable tension a little bit with the adjuster at the derailleur. It
seems to help each time but then, an hour or a day later, the same
thing happens. The chain is not "stretched," and I'm running all
Shimano stuff: Dura Ace shifters, Dura Ace chain, Ultegra cassette, 600
cranks, 105 short-cage derailleur. Nothing is worn, and it's all
clean and lubed. I've never had this problem before, despite having
re-cabled the bike a few times.

Ideas, suggestions?

First, the obvious: is the pinch bolt tight enough? It sounds like the
cable is being pulled out of place very slowly. Also, if you're using a
coated cable, did you remove the coating under the pinch bolt?

Then the non-obvious: how long has it been since you inspected the
housing? If one of the housing ferrules has failed, it could "shorten"
the housing by letting the wires poke through. If the housing is more
than a year or two old, replacing it would be a good idea.

Jeff

Good suggestions. Also check the routing of the cable on the derailer;
if you run the cable on the wrong side of the pinch bolt, you won't be
able to get it adjusted correctly.

--
Dave
dvt at psu dot edu

JeffWills said:

First, the obvious: is the pinch bolt tight enough? It sounds like the
cable is being pulled out of place very slowly. Also, if you're using a
coated cable, did you remove the coating under the pinch bolt?

Then the non-obvious: how long has it been since you inspected the
housing? If one of the housing ferrules has failed, it could "shorten"
the housing by letting the wires poke through. If the housing is more
than a year or two old, replacing it would be a good idea.

Jeff

Thanks for the ideas. It sure seemed like the pinch bolt to me, too,
but I've checked it and it is tight. The cable housings are new (I
replaced them at the same time as the inner wire), and the ferrules all
look fine. It's not coated wire, just plain old Shimano stuff.

dvt said:

Good suggestions. Also check the routing of the cable on the derailer;
if you run the cable on the wrong side of the pinch bolt, you won't be
able to get it adjusted correctly.

--
Dave
dvt at psu dot edu

thanks. I routed it straight. I'm thinking this might just be a case
where a new cable and new housings take a few rides to stretch and get
fully seated.

Josh Hassol said:

I recently re-cabled my rear derailleur. I adjusted the indexing and
got it working perfectly on the work stand. But when I'm out riding,
the derailleur will, from time to time, spontaneously shift to the next
smaller cog. This is not a case of BB flex causing ghost shifting. It
occurs under normal, easy pedaling, and I'm riding one of those older
Cannondale frames with the huge down tube (very stiff).

Quoted message said:

Ideas, suggestions?

On my C'dale I had a similiar problem. What worked for me was to use a
2mm washer. I placed it between the dropout and cassette. Problem
solved.

In article <[email hidden]>,
[email hidden] says...

Quoted message said:

Ideas, suggestions?

Clean and lube the BB guide. That's where I would look first.
--------------
Alex

How did you adjust the indexing? By eye or by feel? I don't have a work
stand at home so just flip the bike over shifted to a middle cog, and
press the jockey wheel down, making sure that it's absolutely,
positively aligned over the sprocket..

Alex Rodriguez said:

In article <[email hidden]>,
[email hidden] says...

Quoted message said:

Ideas, suggestions?

Clean and lube the BB guide. That's where I would look first.
--------------
Alex

Thanks for the suggestion. I did clean the BB guide and lubed it with
tri-flow. So it's not that, I don't think.

landotter said:

How did you adjust the indexing? By eye or by feel? I don't have a work
stand at home so just flip the bike over shifted to a middle cog, and
press the jockey wheel down, making sure that it's absolutely,
positively aligned over the sprocket..

That's an interesting technique. I've never tried that. I'll check it
before my commute home today.

I always follow the procedure outlined in the instructions from
Shimano, or from the Park Tool website, both which, I guess, could be
classified as "by feel."

quote='Josh Hassol'dvt said:

Good suggestions. Also check the routing of the cable on the derailer;
if you run the cable on the wrong side of the pinch bolt, you won't be
able to get it adjusted correctly.

--
Dave
dvt at psu dot edu

thanks. I routed it straight. I'm thinking this might just be a case
where a new cable and new housings take a few rides to stretch and get
fully seated.[/QUOTE]
I think you are on to something here. Sometimes, the cable ends and ferrules are coming together (seating) and effectively shortening the housing.
If you want to force the process you can. Metal ferrules seen to work best for me with true Shimano SIS housing sections. I like to get the "factory" pieces for both shifter and derailer ends.

JeffWills wrote:

.. . . If one of the housing ferrules has failed, it could "shorten"

Quoted message said:

the housing by letting the wires poke through. If the housing is more
than a year or two old, replacing it would be a good idea.

Jeff

Jeff gets the prize! In my original reply, I said that I had checked
the ferrules. But on my ride home last night, when the shifting
problem appeared yet again, I thought, "hell, let me check them again."
Sure enough the housing is not properly seated in the ferrule at the
downtube stop. Instead, the end of the housing is caught on the edge
of the ferrule. It must have done that as I was pulling the cable
through. As a result, some of the housing wires are coming out, and
squeezing down along the outside of the ferrule. This causes the cable
tension to diminish over time.

Easy to fix (tonight), but I never would have checked again if Jeff
hadn't planted that seed in my mind. Thanks!

Josh Hassol said:

JeffWills wrote:

. . . If one of the housing ferrules has failed, it could "shorten"

Quoted message said:

the housing by letting the wires poke through. If the housing is more
than a year or two old, replacing it would be a good idea.

Jeff

Jeff gets the prize! In my original reply, I said that I had checked
the ferrules. But on my ride home last night, when the shifting
problem appeared yet again, I thought, "hell, let me check them again."
Sure enough the housing is not properly seated in the ferrule at the
downtube stop. Instead, the end of the housing is caught on the edge
of the ferrule. It must have done that as I was pulling the cable
through. As a result, some of the housing wires are coming out, and
squeezing down along the outside of the ferrule. This causes the cable
tension to diminish over time.

Easy to fix (tonight), but I never would have checked again if Jeff
hadn't planted that seed in my mind. Thanks!

Good feedback. Thanks.

Lou
--
Posted by news://news.nb.nu

Josh Hassol said:

JeffWills wrote:

. . . If one of the housing ferrules has failed, it could "shorten"

Quoted message said:

the housing by letting the wires poke through. If the housing is more
than a year or two old, replacing it would be a good idea.

Jeff

Jeff gets the prize! In my original reply, I said that I had checked
the ferrules. But on my ride home last night, when the shifting
problem appeared yet again, I thought, "hell, let me check them again."

Vindication! I will do the magic cone dance tonight!
http://photostore.chrisleck.com/gallery/620182/4

Jeff