Gear change weirdness

[Andy in Germany]

I've got an 8 spd cassette on my main bike, and I've just changed the shifter. The gears aren't absolutely perfect at the best of times because it is a long tail bike so the cable is about 15cn/6" longer than usual and this does affect the responsiveness.

This time, however, the shifting is fine in the lower and upper gears, but in the middle it either responds late or not at all untill I shift again, at which point it jumps a gear. This is the same going up or down, although down I can at least push the thumb shifter a bit to encourage it to change.

What I don't understand is that apart from the middle it shifts like normal, so I don't see how it can be the tension. Any ideas?

 

[Yellow Saddle]

Assuming all things equal and the old shifter worked well but was replaced for reasons not pertaining to shifting problems, it is the F-word,

Friction. I don't know how long 15cn/6" is, but it sounds if it is making some unnecessary turns and passes where friction plays a role. Let's see the layout of that cable.

 

[helston90]

When did you last replace the cable and outer? If your shifter is new, and the derailleur you're happy is sitting straight with H - L set correctly I'd be tempted to replace the cabling and housing to help it move as smooth as possible (going back to @Yellow Saddle 's friction comment!)

 

[Nigelnightmare]

It sounds like the replacement shifter has a different pull ratio to the old one.

 

[Andy in Germany]

When did you last replace the cable and outer? If your shifter is new, and the derailleur you're happy is sitting straight with H - L set correctly I'd be tempted to replace the cabling and housing to help it move as smooth as possible (going back to @Yellow Saddle 's friction comment!)

Outer cable a couple of months old and and fresh inner cable too, come to that. I'm wondering the outer cable isn't a bit long, but it's the same as the pre-shifter change one.

 

[Andy in Germany]

It sounds like the replacement shifter has a different pull ratio to the old one.

I wondered that, although I've never heard of it before.

These gears were always a bit iffy, but never this bad.

 

[12boy]

I assume this is a friction shifter? If indexed then it's stops may be off. Many older indexed shifters can be switched back to friction.

 

[Andy in Germany]

I don't know how long 15cn/6" is, but it sounds if it is making some unnecessary turns and passes where friction plays a role. Let's see the layout of that cable.

Ahem, sloppy typing as usual, That's 15cm or six inches.

I assume this is a friction shifter? If indexed then it's stops may be off. Many older indexed shifters can be switched back to friction.

Forgot to mention that. They're rapidfires.

I think it's friction in the cable though. I used the bike to ride to the next village today and on the way back, when it refused to change in either direction I tugged at the exposed cable where it runs on the crossbar, and the gear changed. The next time I had to change up it was the same: click-tug-change. After a while doing this this they seem to be running a bit smoother. I hope so because grasping hold of a gear cable with gloves is a pain.

 

[Levo-Lon]

Id have thought 150mm extra cable shouldn't make much difference.

Check top and bottom are spot on with the H-L screws, check the Back setting.
If there all good then with it in 4 set it with the barrel adjuster so it as quiet as it can be.

If its still sticky and dodgy changes check the derailleur, oil everything to make sure alls moving free.

Another check is to move the cable down shift and see if you can take up any cable slack at the derailleur with your hand?
If it moves then id just get a new cable as it may have a kink or unseen pinch.

 

[Yellow Saddle]

It sounds to me as if there is a kink in the inner cable somewhere before it enters the outer cable.

 

[12boy]

I had a lot of trouble with my Brompton rear brake which has a long and cumbersome cable path. The brake wouldnt return to openbafter using it so I disassembled the brake, greased the pivots etc, but no joy. Replacing the cable and the housing didvthe trick. Apparently it doesn't take a lot of shmutz to bind the cable.

 

[Globalti]

If pulling the cable on the top tube works and operating the shifter doesn't work the simple conclusion is that the cable to the shifter is goosed. New cables all round will transform the shifting. That means outers and inners.

Cable performance deteriorates slowly and people get used to the bad shifting. It's not until they change the cables that they realise how bad it has become.

 

[Andy in Germany]

I had a lot of trouble with my Brompton rear brake which has a long and cumbersome cable path. The brake wouldnt return to openbafter using it so I disassembled the brake, greased the pivots etc, but no joy. Replacing the cable and the housing didvthe trick. Apparently it doesn't take a lot of shmutz to bind the cable.

If pulling the cable on the top tube works and operating the shifter doesn't work the simple conclusion is that the cable to the shifter is goosed. New cables all round will transform the shifting. That means outers and inners.

Cable performance deteriorates slowly and people get used to the bad shifting. It's not until they change the cables that they realise how bad it has become.

I think the problem is more akin to @12boy's trouble with his Brompton, because the cable is long and has to wiggle around the Xracycle frame (I'll take a picture when I have a camera, bike, and daylight.) Also because the cable inner and outer are both new, and also because it is getting better: there's still a delay but it's getting a bit shorter the longer I ride. I think it may need to bed in a bit.

What I don't get though is why it's only the midrange gears: the upper and lower gears are fine.

I can't do anything until the weekend anyway, so we'll see what it is like than and I'l try and take a photo...

 

[CXRAndy]

I would undo the derailleur cable from mech, remove rear wheel and check for free movement of derailleur. if its smooth across its action replace outer and inner cable to rear derailleur

 

[Globalti]

That's the first part of the cabling that deteriorates as the outer cable ends gets rusted and manky. Get your LBS to cut you some pieces to the right length and change the outer every six months.