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Rear Deraileur Cable

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RunningBehind Offline
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Posts: 22
Joined: Jan 2014
Post: #1
Rear Deraileur Cable
I just replaced my rear derailleur with a new one of the same type (Shimano 105).

The only problem I ran into was trying to put the cable back through the barrel adjuster. The end of the cable started to fray, and I could not thread it through anymore. I trimmed a little off the cable, got it threaded, got it attached under the little clamp, and not I no longer have the big cog or the two smallest cogs when I shift.

I am very hesitant to touch the limit screws, as adjusting them without knowing what I was doing is what broke the last derailleur.

Could the problem be that the cable is frayed or is now too short? As a novice at repair, and because the cables run through the inside of the bike frame, should I just take it to my local bike shop?
Feb 3, 2014 08:48 PM
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GeorgeET Offline
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Venice Beach, CA
Posts: 1,162
Joined: Apr 2010
Post: #2
RE: Rear Deraileur Cable
The fraying is not a problem as you usually need to trim the cable length and put a cap on it so it does not fray.

When you put the new cable in the adjustment changed. First start by adjusting your barrel adjusters at the derailleur and handlebar. The screws should not have changed but they are easy to reset. However its the cable you need to adjust. Sounds like its too tight .

http://bicycletutor.com/adjust-rear-derailleur/

Never Give Up!!!
Feb 3, 2014 10:32 PM
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cny-man Offline
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Syracuse, NY
Posts: 409
Joined: Jul 2012
Post: #3
RE: Rear Deraileur Cable
A shorter cable will not affect shifting at all - the derailleur does not know how much cable extends beyond the clamp. Further, it cannot be the cable alone, as that would not affect both ends of the range. If too tight you may not reach the small cog, if too loose you may not reach the large one.

The limit screws on a new derailleur are going to need adjustment, period. They don't know at the factory the exact setup you (or anyone else) has. Luckily the limit screw are intentionally set tight so that you don't just slap on the derailleur and shift into the spokes.

So the first step is to adjust the limits, which is best done separately from the cable tension. Check the above tutorial, partktool.com/blog or sheldonbrown.com for adjustment procedure, but if it's not specified adjust the outer adjustment with the cable tension loose, and adjust the inner limit by pulling on the cable like a bowstring instead of using the lever. Then proceed to adjusting tension for the in-between cogs. If you are not confident in doing the above then take it to a shop or co-op for assistance.
Feb 4, 2014 04:57 AM
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RunningBehind Offline
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Posts: 22
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Post: #4
RE: Rear Deraileur Cable
I guess my concern is how difficult it was getting the frayed cable into the barrel adjuster. It only seemed to make the fraying worse.

Is there any way to stop this fraying?
Feb 4, 2014 06:52 AM
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nfmisso Offline
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San Jose, CA
Posts: 2,333
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Post: #5
RE: Rear Deraileur Cable
(Feb 4, 2014 06:52 AM)RunningBehind Wrote:  I guess my concern is how difficult it was getting the frayed cable into the barrel adjuster. It only seemed to make the fraying worse.

Is there any way to stop this fraying?

Some people attempt to solder or super glue frayed cables - they usually make things much worse, and damage the component (rear derailleur in your case).

I strongly recommend that you replace the cable; you do not need to replace the housing. Just pull the old one out from the shifter, and push the new one through. If you you get a Teflon coated cable, no lubricant is needed. If not coated, wipe a few drops of a light oil (I use TriFlow) on the cable before inserting it. Better quality cables have their ends spot welded together, so that they can't fray during the installation. You still need to cut the cable to correct length - AFTER everything is adjusted and work properly. Use proper sharp cutters designed for hardened cable; regular wire cutters are designed for copper wiring and will not cut bike cables cleanly. Then put a cap on the end to prevent fraying.

Nigel
Feb 4, 2014 09:31 AM
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cny-man Offline
Senior Member

Syracuse, NY
Posts: 409
Joined: Jul 2012
Post: #6
RE: Rear Deraileur Cable
(Feb 4, 2014 06:52 AM)RunningBehind Wrote:  I guess my concern is how difficult it was getting the frayed cable into the barrel adjuster. It only seemed to make the fraying worse.

Is there any way to stop this fraying?

If the cable is slightly frayed one can usually simply twist it clockwise to put the strands back in place. If it's more serious then one can indeed cut it slightly shorter and finish off with shrink-wrap tubing, solder or super glue, as well as the traditional cable end cap. It's not accurate to say people "usually make things much worse," with some of those strategies - just exercise a reasonable amount of care. I see no good reason to replace the cable at this point unless you find it has too much friction to allow easy shifting to the small cogs.
Feb 4, 2014 10:27 AM
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GeorgeET Offline
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Venice Beach, CA
Posts: 1,162
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Post: #7
RE: Rear Deraileur Cable
Yes indeed changing a cable requires length adjustment, The limit screws may need a tweak too, but first cable length(inner) needs to be set . So it has enough length to go through the entire range.

No one said its the cable alone but that the cable change is the first thing to try.

Put the bike upside down and watch how the derailleur moves. Can you manually push it into full arc.(best with cable disconnected) If so your screws are good if not adjust its very simple. Read the ling I provided.

As per fraying if it goes into the outer sheath that's not good. I just at the very tip beyond the clamping screw its OK, but try to contain it.

Try this and than let us know .

Never Give Up!!!
Feb 4, 2014 11:16 AM
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cny-man Offline
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Syracuse, NY
Posts: 409
Joined: Jul 2012
Post: #8
RE: Rear Deraileur Cable
I am sorry, but when one is installing a new derailleur the limit screws need to be set first, as the cable tension is in relation to the derailleur when it is sitting against the outer limit screw. If the derailleur is not underneath the small cog then the tension adjustment will be incorrect. There is no reason to assume that the cable is causing the problem, and again, cable adjustment cannot cause problems at both ends. If the OP replaces the cable he is just inserting more variables, including cable "stretch," which is primarily the housings setting back into place.
Feb 4, 2014 12:31 PM
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RunningBehind Offline
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Posts: 22
Joined: Jan 2014
Post: #9
RE: Rear Deraileur Cable
Thank you all for the responses.

I finally gave up this morning and brought it to the shop. The cable inside the housing was also completely frayed so apparently adjusting the derailleur would not have made a difference.

The cable has been replaced, and the shifting is working as expected.


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Feb 4, 2014 12:58 PM
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GeorgeET Offline
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Venice Beach, CA
Posts: 1,162
Joined: Apr 2010
Post: #10
RE: Rear Deraileur Cable
OOps you are right CNY I missed the part about new derailleur and thought only the cable was replaced. ( Should not answer posts at midnight) Yes set limit screws by manually moving derailleur across gears and than connect and set cable length. Looking at the photo that cable is shoot so the shop made a good call.

Never Give Up!!!
Feb 4, 2014 01:18 PM
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