Hi,
I have been encountering a breakage of the gear cable on my rear derailleur (shimano GRX rx820) roughly every 3-4 months. The strands of the wire unwidins always in the same spot leaving me with a useless transmission that frustrates me. I do long bikepacking trips and I can't have peace of mind with such an unreliable situation.
What are the causes of this flaw, and how can I troubleshoot this?
Thanks in advance!
by No_Cantaloupe_1492
6 Comments
This is due to the design of the shifter: the cable makes a sharp bend in there and the metal fatigues as it bends around it when you shift. There’s nothing you can do about it except replacing the cable frequently.
That is a common malfunction, but your case seems a bit excessive. It may depend somewhat on the quality of the cable you are using. Make sure to use the “slick” stainless steel derailleur cables or the official Shimano coated cables. The reduced friction will extend the life of the cable. Also, make sure your cable path and housing is a smooth as possible. Pulling a dirty cable through dirty housing strains the cable even more.
https://www.reddit.com/r/bikewrench/s/EEcSfYt31x
I had this happen to my 10 speed GRX, same issue only that mine got a bit worse, completely mangled the cable, check the second photo. I cleaned everything and squirted some light synthetic lube in there. So I hope it lasts longer than 3/4 months!
I have to replace my cables about once a year with similar problems. If you have water/dirt/sand that has ingressed into the shifter then it will accelerate this (speaking from experience)
I have modern tiagra and never had this issue it’s been 3 years
I’m not familiar with your GRX shifter in particular, but many Shimano shifters have slick plastic cable guides that hold and guide the cable around that sharp corner….
They also wear, and require replacement, as well as the cables themselves…
On my RS505 shifters, if you don’t replace the guides in time (ps. They are not actually available in my country) the cables start gouging out the supporting plastic shifter chassis until they are beyond repair and need $$$replacement.
I’ve seen guide part numbers, and advise to replace them if required… But I’m unaware of any suggested schedule (distance or time)?
I don’t know for sure, but I wouldn’t be surprised to learn that if the guides are not replaced at the correct interval, it will probably lead to the accellerated cable wear you are experiencing?
It sucks, and seems like a design failure to me, but getting Shimano to admit that and do it for free seems highly unlikely….
It’s simply not an issue for the +90% of bikes that never get past 5000km of use…