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I have been riding my RD-5800 this week with a slightly misaligned hanger. It had some difficult shifting, but it was ridable.

So the hanger alignment tool arrived today, and I decided to clean the derailleur and re-grease the jockey wheels after aligning the hanger. To my incredible surprise, when trying to re-tighten the tension pulley screw, the aluminium forming the thread broke off from the inner plate. I have now a useless derailleur.

I am trying to establish the probable cause of the problem to prevent a similar scenario in the future. Firstly, I would like to precise that the bolt has never been subjected to more than 4 N.m (Shimano max = 5 N.m), so I don't think that is the problem.

Every 2-3 weeks, I remove the jockey wheels to re-grease the bushings. I have been doing that for the last 8 months.

Do you think that the frequent removal of the jockey wheels caused the problem, or it may be due to the vibration experienced by the misaligned hanger?

Follow-up: I have temporarily replaced the bolt with a M5 longer one and a nut on the other side. It is not the better solution, since it is threaded in the bushing portion, but it will last until my new derailleur arrives.

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    "Every 2-3 weeks, I remove the jockey wheels to re-grease the bushings. I have been doing that for the last 8 months." -- why? That's an insane frequency of doing that (probably well beyond the design amount). – Batman Apr 15 '17 at 2:16
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    I've never seen a derailer fail in the way you describe. I suspect that you misthreaded the bolt when you were greasing the bushings. – Daniel R Hicks Apr 15 '17 at 2:38
  • @Batman It was the frequency of washing the bike. I think I may do once every two washes for the new rear derailleur. When washing, you do contaminate the grease with water. That is why I re-greased it. – gstorto Apr 15 '17 at 8:45
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    @GleisonStorto - Don't use water at high pressure to do the washing. I have bikes which have lived outside for years and not needed this type of servicing to have perfectly good shifting. – Batman Apr 15 '17 at 18:41
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    I have never re greased a pulley bushing. Maybe that is why I am slow and people always pass me. – mattnz Apr 15 '17 at 22:39
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It was almost certainly due to repeated removal and re-torquing. Aluminum threads on lightweight bike parts just give up the ghost sometimes in that way even when not mishandled per se.

Plastic bushing-type derailer pulleys really don't much attention in terms of lubrication. I put in a drop of lube every once in a while just to keep them quiet.

One could probably helicoil the stripped cage, but I'm obsessed with helicoiling things :).

  • Another fix may be to fit a bolt through the hole and put the nut on the outside of the bike. Have to watch for binding on the chain in higher gears too. – Criggie Apr 15 '17 at 6:38
  • @Criggie yeah, but I would have to recess the inner plate so it can accommodate a nut the opposite side. The tension pulley bolt is barely long enough to reach the outer part of the inner plate. It could probably be done with a press (pressing the nut into the inner plate). – gstorto Apr 15 '17 at 9:04
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    I meant to replace the whole bolt with a longer one of the same diameter, and fit a nylock nut and washer out the other side. Danger comes if the bolt's head could catch a spoke when in bottom gear, so my dirty trick is to use a bolt with a countersunk head. Or its a replacement cage - try your local bike coop for a spare part for $cheap – Criggie Apr 15 '17 at 23:19
  • I mean, helicoiling it would take 5 minutes and a $1 part if it worked. – Nathan Knutson Apr 16 '17 at 1:25
  • @Criggie Accomplished, but there was no depth left to insert a washer. I will stick with the upper gears until my new derailleur arrives on Wednesday. – gstorto Apr 16 '17 at 6:17

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