smallet

I noticed recently that I have problems switching back from higher cogs to a lower one on the four largest cogs. I have 11 speed Shimano R9100 system with 11-30 cassette. Upon closer examination I think I found why this happens, but I have no idea what's wrong. When I switch down from the largest four cogs, the derailleur frame does not move back as much as required. If I move it with my finger, gears change OK. This looks like a problem with the spring, but I do not have that problem when I move to higher gears (smaller cogs). Also I do not seem to have that problem when I use a large 53 tooth chainring on the front, this only happens with a small 39 tooth chainring. It's like I have to lubricate some parts, but I am not sure where specifically. Any help is much appreciated.

Troul 

how recent has the cable & housing been serviced? Make sure a piece of plastic isn't caught/broken off where the cable feeds through to the mech.

KerryIrons

More likely than a derailleur problem is a cable/casing problem. There is friction somewhere in the system, and the most likely is a corroded or frayed cable.

maddog34

"When I switch down from the largest four cogs, the derailleur frame does not move back as much as required. If I move it with my finger, gears change OK. This looks like a problem with the spring,"

as in.. "the chain remains loose" Or the parallel middle parts of the derailleur are reluctant?

If it's the Chain Tension....
it may be that you have damaged the lower knuckle-to-cage pivot.. i have seen a few derailleurs do exactly what you describe... look for damage on the outer face of the chain cage pivot, or something caught between the cage and lower knuckle, like fishing line, Hair, string, or grass.

also.. look for any bending of the cage...

sometimes a crash can damage the cage or pivot to the point where it will drag and cause exactly what you describe... even the bike falling over in your garage can cause bending or a nick in the cage pivot area.

If it's that the whole Derailleur doesn't swing towards the smaller Gears, yes,the Cable and Housing is most likely your problem, and it MAY be that the Shift cable is About To BREAK INSIDE THE SHIFTER... When did you last replace your Rear Shift Cable? Do It BEFORE it frays and breaks, or suffer the consequences.

See: "Can't get cable end out of right brifter" threads on this and many other forums.

FBinNY 

As mentioned, the most likely cause is cable.

Confirm by detaching the cable and shifting by pushing the RD in by hand, and letting it spring back one step at a time.

If it now shifts fine, the best solution is to replace the cable rather than agonize about where or why it's binding.

choddo

Also if it’s the Shimano coated cables, make sure you put this bit in the rear mech cable capture - helps stop flaked off coating getting into the outer,

for some reason the Shimano manual doesn’t mention it but does show it in the diagram


Or it’s one of the short-tongued covers they also don’t tell you to use there.

smallet

At the first glance, it is probably the cable. I replaced the cable in a bike shop when the original Shimano cable snapped in the middle of a ride. There is no rain where I am living now, the cable looks good, but it is not coated. I think they used some cheaper cable. I checked the cap and I think it is there. But I think this is the place where cable rubs and does move freely when cable tension is high on the lower gears. I will lube the cable and see if it helps.

Also I am quite surprised that Shimano did such a poor job bending cable like this.

RB1-luvr

check your derailleur hanger for alignment.

choddo

Don’t lube the cable! It will attract all sorts of filth.

and yeah, you can see they’ve put the seal with the little tail on properly. If it’s a 9100 they should have looped the excess cable around the pinch bolt and back away from the spokes. Mine is similar to yours though, but without a bend there. The nice thing about those shadow mechs is that part doesn’t swing towards the wheel and ping the cable end into the spokes.

Iride01 

One of the first things I'd do is shift to the smallest cog, undo the cable from the pinch bolt, pull up the hoods and push about two or three inches of cable out of the STI to make certain it's not frayed up inside the STI.

Never mind, I missed your other post. Or was that cable replacement quite a while ago?

choddo

Doesn’t look straight in that photo does it

dedhed

If you think that's a bend, wait until you see inside the shifter

smallet

Yes, I know. Most cables that I replaced had damaged threads inside that shifter. I had a few cables snapped while riding because of this. But in that derailleur it was completely unnecessary. They could have easily made it a straight pull.

smallet

This problem started happening when I shortened my chain. I recently adjusted B-tension. After this it was changing gears better than ever, but then I noticed that my chain is loo long when I have it on the smallest cog in the rear and a small chainring in the front. When I shortened the chain, I started having this gear changing problem. I am not sure what to do now. I think there is too much friction somewhere.

choddo

What made you think the chain was too long? Sag? Chain slap?

small/small should really be avoided anyway.

Are you sure you didn’t close up the mech too near the sprockets when you adjusted the B screw?

smallet

Yes, it was basically sagging a lot.

What happens is the following. When I switch from large cog to a smaller one, the derailleur jumps, but not completely because it is held by the chain rubbing on the cog. When the chain jumps to a lower cog, the derailleur does not move and stays in the half shifted position. The derailleur is obviously not moving smoothly, there is friction somewhere.

bboy314

In addition to hanger alignment, have you checked the chain for wear? And how long ago was the cable replaced? Housing replaced too?

smallet

The chain is new. Housing was not replaced.

When the chain was sagging, the derailleur was moving more freely and would jump to the next position OK. But now the chain tension prevents this until the chain comes to a lower gear. Does this make sense?

choddo

Not sure what you mean by the chain rubbing on the cog. Which cog, the one you were trying to shift out of, or the one you are shifting into? The chain might rub on the cog bigger than the one you want, if the mech isn't putting the chain in the right place properly underneath the selected gear - but that isn't what is stopping it shifting into that gear. It does look to me from one of your photos, as others have suggested, like your hanger is bent - which would cause unpredictable shifting issues. And / or the cable inner & outer needs replacing because that's the most common source of resisting the spring action of the mech trying to pull the chain towards the smaller cogs.

choddo

What does your mech look like when you're in big chainring / 2nd biggest cog? Is the bottom jockey wheel straining forwards?

Worth a watch: (in method 3 he means "to the closest 0.25")

smallet

The derailleur somehow started working better. I think something lapped either in the mech or the cable after its position changed when I shortened the chain. Thank you all for your valuable advice.

smallet

Actually, the gear cable just snapped today. It snapped inside the shifter, just as it usually does. This one did not last a year. The previous cable was from the factory and lasted less than three months. So the problem was due to the cable starting to break. Before the previous one failed, I had somewhat similar experience with shifting, but it failed much quicker after I noticed an issue. I am actually surprised how unreliable Shimano shifters are.

choddo

As per several warnings above

Had one go inside a shifter. It’s ugly. I reckon it happens more if the cable gets twisted during installation.

Kontact

Things to check on Shimano:

Troul 

my initial thought was the cable being suspect.