Rear Derailleur sticking

iman29

iman29

Well-Known Member
Hopefully this question makes sense.

During my ride today I noticed the shifting seemed noisy and then one my my riding buds noticed it seemed like the chain tension wasn’t correct when I was in the smallest cog.

We pulled over and noticed that in the smallest ring the chain was resting on the chain stay and the derailleur seemed like it was stuck but I could move it by hand. I was able to finish the ride by staying out of the smallest 2 rings. Aside from that all shifting was perfectly normal.

Seems that the cage tension is fine as the pulleys will spring back but where the derailleur bolts into the hanger is very stiff.

I’m already resigned to buying a new derailleur because I have an event coming up in a few weeks and I don’t want to have a mechanical DNF. I probably have like 25K miles on this thing too.

Just curious more than anything else since I am no mechanic and really need to learn more And maybe one be able to do some stuff myself.

And no I can’t set it on fire and buy a new bike. I am wishing I had the means to pull the trigger on the Di2 but it’s not in the cards short term right now.


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Disassemble the b-knuckle and lubricate, or try to get some thin stuff in around the seals (work it in by turning the bolt with a hex key).

You can take it apart by pulling the e-clip under the threads, and it will spring apart. Note how everything is together before you do it.

I'm not going to lie, I can pull them apart without too much trouble, but it's fiddly, and I prefer not to.
 
Kinda looks like the derailleur is not attached to the hanger in the correct position?
 
Paul H said:
Kinda looks like the derailleur is not attached to the hanger in the correct position?
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I have it rotated to show how it sticks hence the chain slacked and touching the chain stay.

It’s been working fine since the bike shop did the winter maintenance back in January and I don’t take that stuff apart myself since I have zero skills or tools.
 
iman29 said:
I have it rotated to show how it sticks hence the chain slacked and touching the chain stay.

It’s been working fine since the bike shop did the winter maintenance back in January and I don’t take that stuff apart myself since I have zero skills or tools.
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I wouldn't blame you for knowing your limits, but you only NEED a pair of bigger pliers (like, channellock), a flathead screwdriver, needle nose for replacing the e-clip, the hex keys you already have, and a bit of patience.

There is a slot stamped in the plate that the b-screw goes through--line the e-clip up with the slot using the screwdriver, then remove it (point it at a cloth on the table). You may need to wiggle the metal plate off, or it may spring off, but not violently, typically. Remove the spring, set aside. Push screw out of the knuckle, clean, set aside. Clean the inside of the knuckle, apply a coat of grease to the removed bolt (non-threaded areas). Replace bolt, replace spring. Put plate onto the exposed spring tang, and guide over the bolt threads.

Tricky part: wind tension on the spring until the plate stop passes the stop forged into the derailleur. Smush it all the way together with the big pliers, then get the e-clip partially installed. Grab your needle nose, and finish clipping it in place.

9/10 with newer derailleurs, it's a question of crap stopping the bushing on the mounting bolt from rotating. Spring breakages are really quite rare now.
 
Karate Monkey said:
I wouldn't blame you for knowing your limits, but you only NEED a pair of bigger pliers (like, channellock), a flathead screwdriver, needle nose for replacing the e-clip, the hex keys you already have, and a bit of patience.

There is a slot stamped in the plate that the b-screw goes through--line the e-clip up with the slot using the screwdriver, then remove it (point it at a cloth on the table). You may need to wiggle the metal plate off, or it may spring off, but not violently, typically. Remove the spring, set aside. Push screw out of the knuckle, clean, set aside. Clean the inside of the knuckle, apply a coat of grease to the removed bolt (non-threaded areas). Replace bolt, replace spring. Put plate onto the exposed spring tang, and guide over the bolt threads.

Tricky part: wind tension on the spring until the plate stop passes the stop forged into the derailleur. Smush it all the way together with the big pliers, then get the e-clip partially installed. Grab your needle nose, and finish clipping it in place.

9/10 with newer derailleurs, it's a question of crap stopping the bushing on the mounting bolt from rotating. Spring breakages are really quite rare now.
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I should rephrase my comment. I have tools and some decent DIY skills but for whatever reason I have a phobia of taking the bike apart and making it worse.

I will have to look at some videos to get a better idea of what you suggested to try but I like your theory that it’s just all gunked up in that top spring.

While I was getting my breakfast ready I took the wheel off and snapped a few pics to compare where the B screw is at.

If I rotate the derailleur by hand it doesn’t snap back which leaves the B screw not touching the der hanger tab.

I will have to look at it more during lunch or later tonight after work but appreciate all the suggestions.
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Edit. Yes it’s a little dirty from the last week of riding.
 
I don’t have any experience on non-mtb derailleurs or non Shimano ones, but that sounds very similar to a problem I had with a derailleur I bought used a while ago. It seemed like the chain was too long in the smaller cogs but it was just fine on the bigger ones. It took me a while to figure that out. It turned out the spring that tensions the cage had broken at one end. An attempt at repairing it (or just making it look functional) had been made, which resulted in the spring sliding out of its stop when tensioned (biggest cog) and not pulling back the cage when back in the smallest cog. Tried a repair of the spring but ended up buying a new spring and it worked flawlessly after that.
 
Good news is Ultegra and 105 rear derailleurs appear to be readily available. I had a similar issue and no amount of lube, wiggling, taking apart, etc. would work. Give the lube a shot, but be prepared to buy a new derailleur and maybe cable (because the end will probably fray) pronto if you want to ride that bike on the weekend.
 
goldsbar said:
Good news is Ultegra and 105 rear derailleurs appear to be readily available. I had a similar issue and no amount of lube, wiggling, taking apart, etc. would work. Give the lube a shot, but be prepared to buy a new derailleur and maybe cable (because the end will probably fray) pronto if you want to ride that bike on the weekend.
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good to know and 99.99% this is the plan. I was more just curious what it could be.

also I have a back up road bike so n+1 saves the day for my planned ride this weekend. or since this is a MTB forum break out the MTB and hit some trails. 😝
 
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