4

I have a specialized roubaix of 10 years old. With shimano 105 group. I’m having trouble with my rear derailleur. I want to adjust it so i start on the smallest gear at the back and change gear one by one until i’m on the biggest one. For that part everything works fine. But when i go in the opposite side, it’s all wrong like if the cable or something wasnt coming back like it is suppose to. My cables a new and free in the tubes so it’s probably not that. Does somebody have an idea? Thank you

3
  • 2
    could be too much cable tension. could be gummed up cable/housing. Could be bad spring in the derailleur. Could be other things too, but I think those are the most likely. – Noah Sutherland Apr 27 '20 at 23:47
  • Did you change anything else? I'm guessing its an 8 or 9 speed 105 groupset ? – Criggie Apr 28 '20 at 0:15
  • 1
    Which version of Shimano 105? If you have the 5700 version (10 speed, shifter cables under the bar tape), lift up the top of the right shifter cover and inspect where the shifter cable enters the shifter body. You may have a misrouted cable there that has too much tension to release properly when trying to shift to smaller cogs, since that's done by the tension from the rear derailleur spring. If your cables weren't new, I'd also say to look for fraying at that same point. Where the under-tape cables enters Shimano shifters is a bad wear point for the shift cable because of the sharp bend. – Andrew Henle Apr 28 '20 at 2:03
4

It sounds like you are having trouble downshifting from any larger gear to a smaller one.

If a rear derailleur won't go from a larger gear to a smaller gear it's because:

  • The cable is binding preventing the derailleur from getting enough slack
  • The derailleur spring is too weak

Starting from a smaller gear on a 105 rear derailleur and moving to a larger gear happens because of tension on the cable. You move the lever and it pulls the cable which moves the derailleur. As the derailleur moves a spring in the derailleur is compressed storing energy.

When you move the lever to shift from a larger gear to a smaller gear the cable is given slack. The rear derailleur spring takes up the slack and moves to the smaller gear.

Get the bike on the rack or into a position where you can pedal and make the rear wheel move.

You can test to see if the cable is binding by:

  • Disconnecting the cable from the derailleur
  • Hold the just disconnected end in one hand and move the shift lever with the other. The cable should move easily in both directions.

If you feel any binding you'll need to hunt down the source and fix it.
It could be due to dirt/rust in the housing, a kink in the housing, a kink or hard bend in the cable etc.

With the cable disconnected you can test the derailleur spring by:

  • Turning the pedals with the rear wheel spinning
  • With the rear wheel moving use your hand to move the derailleur to shift into the larger gear.
  • Release the derailleur - keep pedaling - the spring in the derailleur should crisply shift back into the smaller gear.

If the derailleur won't move the chain from the larger gear to the smaller gear the spring may be weak or broken.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.