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Cannondale rear shifting problem

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Cannondale rear shifting problem

Old 05-14-18, 07:48 PM
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milktree
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Cannondale rear shifting problem

Hi everyone.

I'm new to this forum, so hopefully I won't break any unspoken rules in my first post.

My background: I worked as a professional bicycle mechanic for three summers back when dinosaurs roamed the earth ('90-'92), and I've been a semi-professional motorcycle mechanic more recently, but not currently. (the contrast between a motorcycle chain and a bicycle chain is kind of hilarious)

My wife and I have a '12 Cannondale tandem which we bought used last year.

I can't get the rear shifting to work right.

It's a 10 speed Shimano Ultegra setup. (triple front, but that shouldn't matter here)

Here's what I've done:
  • trimmed/squared/polished all the cable housing ends and replaced the endcaps with aluminum ones
  • replaced the cable
  • verified the derailleur hanger is straight
  • verified the bushings in the derailleur are tight
  • verified the derailleur cage is straight
  • chain and cassette were new shortly before we bought the bike (according to the seller, and they look/feel good)
  • shifter and derailleur work: I hooked up the shifter directly to the derailleur with only the final cable housing between them and it shifted well
  • set up the high limit, low limit, and "B-tension" screw according to years of practice (and instructions, just to be sure)
Here's the symptoms:
  • When in the highest gear (smallest cog) and I shift once (to a lower gear, second smallest cog) the derailleur barely moves, and it doesn't shift. If I pull on the cable (at the downtube) it'll jump down a couple gears, and then settle quietly in the second smallest cog. If I then up shift, it shifts cleanly to the smallest cog.
  • Once the derailleur is part way up the cassette, it'll shift normally (both up and down) all the way to the largest cog, and up cleanly all the way all the way to the smallest cog.
  • I clipped a bunch of wooden clothespins on the derailleur cable at various places to measure cable travel. At the top of the top tube it's "big" like about 1.75mm At the entry to the derailleur housing on the chainstay, it's more like .60-.75mm (so, that's wrong) between the two bottom brackets (boom tube? bottom tube?) it's much closer to 1.75mm, but not quite (hard to measure, I haven't figured out the right technique yet)
  • on either side of the rear BB pulley the distance is different.
Therefore: that pulley is doing something wonky.

This is what the setup looks like (a slightly modified extract from page 18 of the 2009 tandem suplemental)

(grrr... I'd usually do this inline with nice thumbnails, but no URLs for newbies! Sorry about the huge image at the bottom)
(edit again... apparently even that doesn't work.)

try this : (remove the spaces)

mahonkin dot com /~milktree/bicycle/tandem/ stoker-cable-guide.jpg

and our particular one:

mahonkin dot com /~milktree/bicycle/tandem/ stoker_cable_routing.JPG

The cable goes through the red thing, and that appears to be mucking it up.

So here's my questions:
  • Do these things fail like this regularly? (is it common? How long do they typically last?)
  • Is there anything else that could be causing this?
  • If not, where the hell does anyone find specialty parts like that in the US? They're easily available in the UK and Germany!
  • Is there a better way to fix this than replacing that part?
  • What tests have I screwed up? (what's wrong with my diagnosis process?)
Thanks!

Last edited by milktree; 05-17-18 at 09:37 AM.
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Old 05-15-18, 07:25 AM
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I have never seen cables routed like this before, but then again, I have never owned a 'Dale.

The behavior you describe is not unfamiliar to me. I forever seem to be tweaking the rear derailleur cable to balance between crisp upshifts to smallest cog with no downshift from smallest cog (your case) and no upshift to smallest cog with crisp downshift from smallest cog. I think there is a cable length window of about 2 fempto meters where both work :-).

I can offer 2 suggestions here:

1- I just live with the non-completing downshift (to larger cog) and just click the brifter again or nudge it just a bit to complete the shift (there is nothing you can do to address the other case). Its a pain, but one just naturally shifts as many times as necessary to achieve the desired gear ration without thinking too much about it.

2- I have seen and personally experienced that lot of rear shifting issues being caused by that short length of cable housing that runs between the chain stay and the rear derailleur. Once it develops wear and exhibits any sort of impedance to cable movement things go wonky. You might replace this with new and a new derailleur cable. I have also found that slightly longer housing with a wider sweep to behave better.
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Old 05-15-18, 09:13 AM
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It sounds to me like a classic case of too much friction on the rear derailleur cable. You should start by lubing the cable housings and that red disc. It's also worth checking all the cable entry points for burrs or misalignment between the cable housing center and the cable stop on the frame.

I haven't seen that red disc approach before. It seems like an awefully convoluted cable guide to me. I believe it's just a straight hole through it. Newer Cannondale tandems have a 1-piece molded cable guide like most other bikes, but they're model-specific. You might browse Cannondale Experts for something that looks like it would fit (https://www.cannondaleexperts.com/Cable-Guides_c_7.html).
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Old 05-15-18, 11:07 AM
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Originally Posted by Alcanbrad View Post
I have never seen cables routed like this before, but then again, I have never owned a 'Dale.

The behavior you describe is not unfamiliar to me. I forever seem to be tweaking the rear derailleur cable to balance between crisp upshifts to smallest cog with no downshift from smallest cog (your case) and no upshift to smallest cog with crisp downshift from smallest cog. I think there is a cable length window of about 2 fempto meters where both work :-).

I can offer 2 suggestions here:

1- I just live with the non-completing downshift (to larger cog) and just click the brifter again or nudge it just a bit to complete the shift (there is nothing you can do to address the other case). Its a pain, but one just naturally shifts as many times as necessary to achieve the desired gear ration without thinking too much about it.

2- I have seen and personally experienced that lot of rear shifting issues being caused by that short length of cable housing that runs between the chain stay and the rear derailleur. Once it develops wear and exhibits any sort of impedance to cable movement things go wonky. You might replace this with new and a new derailleur cable. I have also found that slightly longer housing with a wider sweep to behave better.
Ugh... "just live with it" is ... less than ideal. There's no way Cannondale sold a $4k bike that was like that. Therefore something's wrong. (and it's really annoying!)

the last cable housing was new before we bought the bike, at least the seller said it was. It seems to be quite smooth, and when I hooked the shifter up to the derailleur directly using that housing it functioned fine. I can totally imagine that the PO used too short a cable, but.. it looks like it's got a good radius.

Testing suggests the problem isn't at the final housing, but at the wonky stoker's BB cable routing thingie. (based on cable movement)
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Old 05-15-18, 11:14 AM
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Originally Posted by OneIsAllYouNeed View Post
It sounds to me like a classic case of too much friction on the rear derailleur cable. You should start by lubing the cable housings and that red disc. It's also worth checking all the cable entry points for burrs or misalignment between the cable housing center and the cable stop on the frame.
It's all lubed everywhere The cable housings are all freshly cut square and the inner housing open. New derailleur cable too. No burs anywhere I can find. The "braise-ons" on the frame have an insert that separates the cable from the metal, so I'm pretty confident there.

I haven't seen that red disc approach before. It seems like an awefully convoluted cable guide to me. I believe it's just a straight hole through it.
Yes, that's correct. Offset mounting hole, straight through cable hole.

You might browse Cannondale Experts for something that looks like it would fit (url removed because fewer than 10 posts!!) .
Oh! That's a good site! It's in the US, and they admit the part (kit) exists! Thanks!
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Old 05-15-18, 11:58 AM
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I think you simply have too much slack in the cable when it's all the way down in the smallest cog. Tighten the adjuster on the RD 1/2 turn (CCW). Repeat until it shifts to that 2nd cog. Then run all the way up and back. Should work. When I install a cable, I always build in a couple turns of slack in one of the cable adjusters, then tighten the bolt with what appears to be a tight cable. Sometimes that's too tight but I can loosen the adjuster. Sometimes I need more adjuster. If I need too much, I back the adjuster all the way off, try again with the cable bolt.
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Old 05-15-18, 12:08 PM
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Originally Posted by Carbonfiberboy View Post
I think you simply have too much slack in the cable when it's all the way down in the smallest cog. Tighten the adjuster on the RD 1/2 turn (CCW). Repeat until it shifts to that 2nd cog. Then run all the way up and back. Should work. When I install a cable, I always build in a couple turns of slack in one of the cable adjusters, then tighten the bolt with what appears to be a tight cable. Sometimes that's too tight but I can loosen the adjuster. Sometimes I need more adjuster. If I need too much, I back the adjuster all the way off, try again with the cable bolt.
No, it's not that. See "professional bike mechanic", and "followed the instructions", above. I've adjusted a *lot* of index shifters on a lot of different bikes. I'm pretty confident I know what I'm doing in that respect.

That technique works when there isn't something "squishing" in the cable path. when I do that on this bike, it shifts to the next lower gear, but then the cable is way too tight for the *next* lower and all subsequent lower gears.

If I click once from the smallest cog, the derailleur moves just a tiny bit, not enough to shift. But if I pull the cable and release it, then click "up" to the smallest cog, it moves quite a lot, (the appropriate amount)
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Old 05-15-18, 12:08 PM
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Originally Posted by milktree View Post
Ugh... "just live with it" is ... less than ideal. There's no way Cannondale sold a $4k bike that was like that. Therefore something's wrong. (and it's really annoying!)

the last cable housing was new before we bought the bike, at least the seller said it was. It seems to be quite smooth, and when I hooked the shifter up to the derailleur directly using that housing it functioned fine. I can totally imagine that the PO used too short a cable, but.. it looks like it's got a good radius.

Testing suggests the problem isn't at the final housing, but at the wonky stoker's BB cable routing thingie. (based on cable movement)
I hear you. I think it is inherent in tandems due to accumulated cable slack in the long cable runs. You can see this be trying the following: Put the derailleur in the highest gear. Shift down one and while pedalling adjust the barrel adjusters to take up the cable slack and cause the derailleur to shift to the expected cog (i.e. where you would expect it be). Now try shifting around and see if it will successfully shift from the next to smallest to smallest cog. Eliminating ALL friction in the entire cable run is the best you can try and accomplish. All new super low friction compression-less housings is an expensive try, however, I am afraid that you will be futzing forever (or just living with it).
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Old 05-15-18, 01:18 PM
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Originally Posted by milktree View Post
No, it's not that. See "professional bike mechanic", and "followed the instructions", above. I've adjusted a *lot* of index shifters on a lot of different bikes. I'm pretty confident I know what I'm doing in that respect.

That technique works when there isn't something "squishing" in the cable path. when I do that on this bike, it shifts to the next lower gear, but then the cable is way too tight for the *next* lower and all subsequent lower gears.

If I click once from the smallest cog, the derailleur moves just a tiny bit, not enough to shift. But if I pull the cable and release it, then click "up" to the smallest cog, it moves quite a lot, (the appropriate amount)
Next guess is that it's still a cable end problem or similar. With Shimano 10sp, worst problem I've had with that sort of thing is where the cable exits the brifter into the housing under the bar tape. Maybe the tape is pre-tensioning the housing. Try untaping, shift all the way to the biggest cog, make sure the housing is tight in its receptacle, retape with the cable tight.
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Old 05-15-18, 01:47 PM
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Originally Posted by Carbonfiberboy View Post
Next guess is that it's still a cable end problem or similar. With Shimano 10sp, worst problem I've had with that sort of thing is where the cable exits the brifter into the housing under the bar tape. Maybe the tape is pre-tensioning the housing. Try untaping, shift all the way to the biggest cog, make sure the housing is tight in its receptacle, retape with the cable tight.
I haven't re-taped the bars since I fixed the poorly cut housing Currently there's *no* tape on the bars.

when I make the first shift, the housing doesn't move (at least I can't feel it with my finger across the housing and brifter chassis)

And, the cable movement coming out of the first housing (the one at the top of the downtube) appears to be plenty, it's about 1.75mm

Maybe I'll use automotive feeler gauges to measure the pull...
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Old 05-15-18, 02:45 PM
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Originally Posted by milktree View Post
I haven't re-taped the bars since I fixed the poorly cut housing Currently there's *no* tape on the bars.

when I make the first shift, the housing doesn't move (at least I can't feel it with my finger across the housing and brifter chassis)

And, the cable movement coming out of the first housing (the one at the top of the downtube) appears to be plenty, it's about 1.75mm

Maybe I'll use automotive feeler gauges to measure the pull...
So the cable pull at that first cable stop seems the same for every pull, including the first one? No need to reply to that. Therefore something's moving like it's spring loaded somewhere down the line. The first pull is just taking the slack out of whatever it is. So after you've shifted all the way down, there should be some movement in some component - the last housing to the RD, the mount for that little pulley, something. Maybe someone could watch for movement while you actuate the shifter to shift up from that 1st cog. Something's moving somewhere.

We got better shifting performance after replacing all the shift housing with Alligator housing: Alligatorilink Cable Kit - ALLIGATOR
Really fixed all our "have-to-nudge-the-lever" shifting problems.
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Old 05-15-18, 03:18 PM
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Will share a similar challenge I had once.
changed RD cable on mtn tandem. Just could not get it to work correctly. Upon careful scrutiny the cable was stretching under tension.
Changed cable to normal brand of cable that I usually use.
Viola, perfect shifting again.
i now have a note on my parts cabinet to never buy that brand/model of cable that gave me fits.
Yes, I tried all the usual things to no avail.
i even put the suspect cable back in after solving the issue to verify that it was the problem. Yup, it still sucked.
Been wrenching for more years than I care to say and never ran into this before.
This information may or may not help but is a data point to consider.
Also noticed some brands will break after normal life span at derailleur fixing bolt while others consistantly at the shifter. Some last longer than others etc. Have many bikes and have been wrenchimg long enough to see the differences.
Good luck.
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Old 05-15-18, 08:55 PM
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Originally Posted by milktree View Post

Oh! That's a good site! It's in the US, and they admit the part (kit) exists! Thanks!
I like them a lot, they helped me find the only 120mm stem, compatible with my fatty fork, on the planet.

Agree that the routing under the bottom bracket looks really gnarly.
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Old 05-16-18, 05:08 PM
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You've got the cables set up correctly; same as on my 2009 RT2. Mine shifts great, new cables a few thousand miles ago. I do think I have to over shift just a little past the click, but not much. Lots of cable to stretch and housing to flex/compress.
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Old 05-16-18, 05:34 PM
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I too have a Cannondale tandem with the cable routing as pictured by Scraper. The shifting has worked fine, with an occasional adjustment, for several thousand miles.

Originally Posted by milktree View Post
...trimmed/squared/polished all the cable housing ends and replaced the endcaps with aluminum ones
Are these the correct ferrules for the cable housing you are using? Most modern housings require a plastic ferrule that is designed to keep the individual strands of shifter housing wire from slipping past the end of the housing plastic. Make sure you have the correct ferrules for the housing you are using.
Other things to check:
Did the previous owner replace the shifter cable housing (linear strands) with brake cable housing (coiled flat wire)?
I concur with the previous suggestion to replace the rear section of cable housing and its ferrules. This area is a frequent culprit and the replacement parts are cheap. A housing that is too short can cause binding and a housing that is too long can flex laterally causing incrementally less pull at the rear derailleur.
Brent
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Old 05-17-18, 09:22 AM
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Originally Posted by obrentharris View Post
I too have a Cannondale tandem with the cable routing as pictured by Scraper. The shifting has worked fine, with an occasional adjustment, for several thousand miles.



Are these the correct ferrules for the cable housing you are using? Most modern housings require a plastic ferrule that is designed to keep the individual strands of shifter housing wire from slipping past the end of the housing plastic. Make sure you have the correct ferrules for the housing you are using.
er... I'm not sure. What do you mean "slipping past the end of the housing plastic"? The inner housing (teflon?) and the longitudinal steel strands and the outer plastic cover are all the same length, cut square. The ones I've got on now are aluminum. The derailleur's service manual says specifically to use "the aluminum end" at the derailleur, but doesn't specify anything special for any of the other ends.


Other things to check:
Did the previous owner replace the shifter cable housing (linear strands) with brake cable housing (coiled flat wire)?
Nope, linear. Made by Jagwire.

I concur with the previous suggestion to replace the rear section of cable housing and its ferrules. This area is a frequent culprit and the replacement parts are cheap. A housing that is too short can cause binding and a housing that is too long can flex laterally causing incrementally less pull at the rear derailleur.
So.. based on other derailleurs, it looks right. No kinking, no flopping. Any day now I'll be able to post pictures.
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Old 05-17-18, 09:28 AM
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Originally Posted by Carbonfiberboy View Post
So the cable pull at that first cable stop seems the same for every pull, including the first one? No need to reply to that. Therefore something's moving like it's spring loaded somewhere down the line. The first pull is just taking the slack out of whatever it is. So after you've shifted all the way down, there should be some movement in some component - the last housing to the RD, the mount for that little pulley, something. Maybe someone could watch for movement while you actuate the shifter to shift up from that 1st cog. Something's moving somewhere.
Yea... I'm pretty sure it's at the disk thing under the stoker's BB, "pull distances" for the first click seem sane before it, and "too short" after.

We got better shifting performance after replacing all the shift housing with Alligator housing: (url removed because too few posts... )
Really fixed all our "have-to-nudge-the-lever" shifting problems.
Woah.... That's neat. Their website is kinda craptastic, can you literally pull off or add links to change the length? (and trimming/replacing the core, obviously) Does it function just like regular housing?
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Old 05-17-18, 09:31 AM
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Originally Posted by Scraper View Post
You've got the cables set up correctly; same as on my 2009 RT2. Mine shifts great, new cables a few thousand miles ago. I do think I have to over shift just a little past the click, but not much. Lots of cable to stretch and housing to flex/compress. (image removed, only a few posts to go!!)
Your garage looks a lot like mine! (different motorcycle, no concrete)

any chance you can take a close-up picture (or pictures) of the little disk guide? Specifically the entrance/exit holes? I wonder how worn mine is.
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Old 05-17-18, 09:41 AM
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And while I'm using up initial posts...

Are there shift cable manufacturers that are generally known to be less stretchy than others?
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Old 05-17-18, 10:07 AM
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Originally Posted by milktree View Post
Yea... I'm pretty sure it's at the disk thing under the stoker's BB, "pull distances" for the first click seem sane before it, and "too short" after.



Woah.... That's neat. Their website is kinda craptastic, can you literally pull off or add links to change the length? (and trimming/replacing the core, obviously) Does it function just like regular housing?
Yep, just de-section to length, no cutting. I have all my cables covered with that core, full length except where I can't. Keeps them cleaner.

I'd talk to a dealer (Tandems East?) or someone about the disc. I don't think that's stock. There's usually a grooved or tubed plate that goes there.
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Old 05-17-18, 08:16 PM
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Originally Posted by milktree View Post
.....

Woah.... That's neat. Their website is kinda craptastic, can you literally pull off or add links to change the length? (and trimming/replacing the core, obviously) Does it function just like regular housing?
Jagwire also makes a compression less cable housing made up of individual 10mm aluminum barrels. We have them on our co-mo and are quite happy. I plan on switching to them on my single when the time for new housing comes back around. Look for jagwire elite cable sets. Not cheap though.
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Old 05-17-18, 10:23 PM
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I have Jagwire stainless for all cables and I have one continuous length of Jagwire compressionless housing for the rear brake.

Jagwire does state the you should use continuous housing whenever possible to eliminate the added friction on the cable entering and leaving the housing multiple times. But if you have it run just like factory.... It seems to me if you are hanging up only on the last cog, that the issue is with the derailleur and not the cable.
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Old 05-18-18, 05:00 AM
  #23  
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Originally Posted by Yamato72 View Post
....... It seems to me if you are hanging up only on the last cog, that the issue is with the derailleur and not the cable.
I believe this is only partially true. The cause is most likely due to the cumulative friction and slack in the run of cable that is not able to be overcome by the derailleur parallelograms return spring. Component manufacturers strive to make the force you have to apply for shifting as light as possible which results in specifying the return spring to provide “just enough” force to overcome the friction and slack inherent in the cable path for a single bike. They are designing to the market and that is the single bike.

Repeating what I said earlier, you can see this for yourself: Put the derailleur in the highest gear. Shift down one and while pedaling adjust the barrel adjusters to take up the cable slack and cause the derailleur to shift to the expected cog (i.e. where you would expect it be). Now try shifting around and see if it will successfully shift from the next to smallest to smallest cog.

When the derailleur should be in the smallest cog you can feel less tension in the cable. If you applied a little force on the derailleur it would shift and the cable tighten. Similarly if you were to cut the cable close to the derailleur it would shift as the return spring would not be held back.

So yes, the problem is that the derailleur cannot overcome the friction and slack, however we tend to focus on the cable as that is about the only element of the system we can tweak.

One thing I have thought about trying but have never gotten around to, is to play with the limit stop screws on the derailleur to operate it in a region where there is more tension on the return spring. I don’t know if there is enough range available to make a difference. Has anyone thought about or tried this?

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Old 05-18-18, 05:52 AM
  #24  
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Originally Posted by Yamato72 View Post
I have Jagwire stainless for all cables and I have one continuous length of Jagwire compressionless housing for the rear brake.

Jagwire does state the you should use continuous housing whenever possible to eliminate the added friction on the cable entering and leaving the housing multiple times. But if you have it run just like factory.... It seems to me if you are hanging up only on the last cog, that the issue is with the derailleur and not the cable.
Except that when I hooked up the shifter directly to the derailleur using only the rear housing it shifted just fine.

Also, I'm hanging up on the first shift from highest gear, but only in one direction.

If it's in the highest gear, and I click once... nothing. If I pull the cable with my hand and shift down three for four gears, and then let go, it drops into the second highest gear, not the highest gear. one upshift click shifts cleanly.
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Old 05-18-18, 07:43 AM
  #25  
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Have you tried a different cassette? I once exchanged a new cassette at REI when I had shifting issues on one cog only. The replacement cassette worked fine. I’m not suggesting it is a likely solution but given that nothing else has yet solved the problem and trying another cassette is easy to do, might be worth a try?
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