Rear Derailleur Cable Breaking (Shimano)

Discussion in 'Shop Talk' started by knucklebuster, Nov 15, 2014.

  1. knucklebuster

    knucklebuster MTB Addict

    Location:
    Mission Viejo (South Orange County)
    Name:
    Dave
    Current Bike:
    Canfield The One '12
    I've had two myself (second today) and witnessed one other in the last few months, breaks right at the cable clamp (see pic). I thought I remembered finding something on the interweb when my first one broke saying it was somewhat common, but now I cannot get the google to give me what I'm looking for. It's a Shimano XT M786 Shadow+ 10 speed.
    Anyone experience this and/or have an idea of why and what can be done to MAKE IT STOP? I started carrying a spare cable in my pack, today I was close and mostly downhill enough that I just re-clamped it to get usage of the 5 big cogs. But I never had this happen until I went to Shadow+ so wondering if there is know issue and fix. Thanks!

    IMAG0528.jpg
     
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  2. herzalot

    herzalot MTB Addict

    Location:
    Laguna Beach
    Name:
    Chris
    Current Bike:
    '15 Intense Tracer 275c DVOish
    How tight is your Shadow Plus set? If it is hard to push with your thumb, there is some unusual stress on the cable.

    The guys at BikeCo told me that breaking rear derailleur cables might be caused by gear hunting. That is, let's say you are climbing in your bigger ring and are on the biggest cog in back. You pump your thumb a couple of times to see if you have an easier gear available before you dump to the little chainring. That bumping against the stop puts a ton of unfriendly pressure on the cable.

    I stopped doing it, and I stopped breaking cables. Luckily, my right thumb lever has a "loose" feel to it when it is already at the easiest gear, telling me I have no room left to go up, and "do not press."

    Another possibility is that your chain is too tight. You may be pulling the derailleur to its extreme when your suspension cycles if your chain is too tight.

    So there are three possibilities that I can think of Dave. I hope it's an easy solution.
     
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  3. knucklebuster

    knucklebuster MTB Addict

    Location:
    Mission Viejo (South Orange County)
    Name:
    Dave
    Current Bike:
    Canfield The One '12
    Thanks for the suggestions Herz, got me thinking some more... I think I have all those boxes checked, easy thumb push on the shifter, have the loose shifter feel when in big cog so not pushing against the stop, and chain plenty long. I remember now (vaguely, old ya know) another forum poster recommended filing a little of the edge off the "perch" where the cable goes to the clamp, as that seems to be the point of breakage (maybe the angle gets too big, or the edge is too sharp?).

    Ready for a new chain anyway so will double check that and may run new housing to make sure there are no tight bends, air down the shock and see if it stresses the cable anywhere in the travel, etc., or just buy a new bike. :ugeek:
     
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  4. Mikie

    Mikie Admin/MTB Addict

    Location:
    Lebec, California
    Name:
    Mikie Watson
    Current Bike:
    Yeti ASR5c, SC Hightower
    WOW!
    That pic looks like the pic I took of my bike Friday night. Accept my cable looked like it been like that for a week all completely unraveled. I'm wondering how I even finished the Cannell Plunge last week.

    Another possibility was suggested by rossage. I have the same XT rear derailleur and he was having the same problem. He took a tiny round file and rounded the edge of the slot where the cable first comes in contact with the derailleur. He noticed it had a sharp edge and that it was potentially working the cable back and forth to the point of breaking the threads one at a time. You probably would not even notice it until it was getting closer to failure. rossage said that once he did that the problem went away.

    Maybe a combo of that and what Herz said could be the culprit! Hope this helps!

    Mikie
     
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  5. mike

    mike MTB Addict

    Location:
    Western US
    Name:
    Mike O
    Current Bike:
    Guerrilla Gravity Smash
    The sharp-edge theory sounds and looks plausible.

    Some like metal ferrules versus plastic because they straiten out the routing a little. fwiw.

    My wrenches at the Path are propping a new Shimano cable (polymer coating IIRC) which they recently got in.

    All suggestions worth what they cost ya, maybe less...
     
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  6. Rob S.

    Rob S. Well-Known Member

    Location:
    La Habra, CA
    Name:
    Rob Skinner
    Another thing to confirm is that you only clamp the cable ONCE. Get your drive train set up just right, your shifter an your derailleur exactly where they need to be, carefully place the cable in the clamp, and slowly tighten the screw ONCE. If you jack around clamping and unclamping to get things just right, your cable won't last long. You might even break some strands before you're done.
     
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  7. knucklebuster

    knucklebuster MTB Addict

    Location:
    Mission Viejo (South Orange County)
    Name:
    Dave
    Current Bike:
    Canfield The One '12
    Thanks for the suggestions everyone. I filed the edges off the perch/hole thingy where the cable clamps. Spoke to a guy at the path live oak and he said they see quite a few of these, and taking the edges off usually does the trick. Makes sense if you watch the cable angle at that hole it goes from bent one way in small cog to bent the other way in large. Probably back and forth fatigueTM on each edge does it in eventually.
    For good measure, new cable housing and chain, so drivetrain should be good to go for awhile. Now waiting to get my Reverb back from the Path for a rebuild, and do a fork oil and seal change, and all will be hunky dorey (until the next thing happens....).
     
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  8. UPSed

    UPSed MTB Addict

    Location:
    Simi Valley
    Name:
    Edward Bottorff
    Current Bike:
    Niner Jet 9 RDO Plus
    Yep. Every Shimano Shadow derailleur I've had eats cables. I guess it's time for me to break out my round file.
     
  9. DangerDirtyD

    DangerDirtyD MTB Addict

    Location:
    La Verne, CA
    Name:
    Dennis (AKA Dio)
    Current Bike:
    2013 Trek Slash 9 (26er)
    It’s about time you chimed in Ed.
     
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  10. UPSed

    UPSed MTB Addict

    Location:
    Simi Valley
    Name:
    Edward Bottorff
    Current Bike:
    Niner Jet 9 RDO Plus
    Haha! I just accepted it as a design flaw and just kept changing them every few months.
     
  11. herzalot

    herzalot MTB Addict

    Location:
    Laguna Beach
    Name:
    Chris
    Current Bike:
    '15 Intense Tracer 275c DVOish
    Yup - 4 years later...
     
  12. Faust29

    Faust29 MTB Addict

    Location:
    Rancho Santa Margarita
    Name:
    Steve
    Current Bike:
    Chameleon & Highball C
    Ha-hem... Cough. 2014. Cough. Little late. Cough.

    I needed a little humor today. You guys came through. :D
     
  13. UPSed

    UPSed MTB Addict

    Location:
    Simi Valley
    Name:
    Edward Bottorff
    Current Bike:
    Niner Jet 9 RDO Plus
    Next time I do a Google search I will remember not to click on anything that is from imtbtrails. Apparently there is no useful information here. Thanks.
     
  14. Obsidian

    Obsidian Well-Known Member

    Location:
    Costa Mesa
    Name:
    Obsidian
    Current Bike:
    2017 Intense Tracer
    When I had a Shadow, I broke the cable in that exact spot about every six months. It got to the point where I started carrying a spare every ride.
     
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  15. Runs with Scissors

    Runs with Scissors MTB Addict

    Location:
    West Anaheim
    Name:
    Mark Whitaker
    Current Bike:
    2015 Giant XTC Advanced 1 29er
    Doing my part to contribute to thread necrosis....

    I'll admit I've never broken one on either of my Shadow Plus derailleurs. I saw one start to fray once, so I replaced it immediately.
     
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  16. herzalot

    herzalot MTB Addict

    Location:
    Laguna Beach
    Name:
    Chris
    Current Bike:
    '15 Intense Tracer 275c DVOish
    Me too and me too. I still carry a spare, but haven't broken one with my SRAM. I still like Shimano better.
     
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