front derailleur problem - it's acting like a triple - help

petemadoc

I've got a Shimano 105 compact chainset 50/34 and everything's been running fine and dandy until I had some issues with loose bolts and wobbly pedals. These are all sorted now but the front derailleur is playing up, here's the symptoms.

I push the shifter and the mech moves up but it doesn't move enough to shift the chain up. Then I can push the shifter AGAIN (I never used to be able to do this) and it moves enough to shift the chain up to the big ring. Exactly the same scenario when shifting down. It's like it's suddenly got three settings instead of two like a triple? ?

The upper and lower limits are set ok, it's like when you push the shifter it doesn't move the mech the whole distance, just half way and then you have to push the shifter again

Anyone got a fix for this?

father_jack

Isn't that the trim adjustment? My two Campag triples do that it takes 2 clicks to move FD. It's there so you can get rid of a little bit of chain rub if you're in certain gear combinations.

petemadoc

No it's not the trim

With each shift that I'm talking about there is also the trim adjustment. So when shifting down you can click (trim) then shift, then click (trim again) then shift again. Definitely two full shifts up and down.

Buckled_Rims

Change stretch causes all sorts of problems. Usually unable to change from small to large.

105 LH shifters are generally triple anyhow and also cause cack loads of problems.

petemadoc

Buckled_Rims wrote:

Change stretch causes all sorts of problems. Usually unable to change from small to large.

105 LH shifters are generally triple anyhow and also cause cack loads of problems.

Hmm great.

I guess what I need to know is how to make one single push on the shifter move the mech further in one go rather than taking two shifts to get right across.

Buckled_Rims

PeteMadoc wrote:

Buckled_Rims wrote:

Change stretch causes all sorts of problems. Usually unable to change from small to large.

105 LH shifters are generally triple anyhow and also cause cack loads of problems.

Hmm great.

I guess what I need to know is how to make one single push on the shifter move the mech further in one go rather than taking two shifts to get right across.

On most 105 LH shifters on a double or compact, from small to large cogs is one shift. Going down from large to small is 2 clicks.

Yeah, I know, it's crap!

Cleat Eastwood

Slack cable.

Pokerface

Can you not set it up so the lower limit of the mech is where the middle ring would be?

Thus making the triple shift work like a double? A combination of the correct cable tension and setting the upper and lower limit screws on the mech should fix this.

satanas

1. Look under the rubber hood and find the part number of your STI lever on the body.
2. Go to the Shimano website and download the relevant service instructions.
3. Read, then follow them, starting from the beginning.
4. If it's still not working properly, either ask another question here or visit your LBS.

Sometimes triple (and "triple/double compatible") STI levers can be a pain, when used with either triple or double cranks/derailleurs. IME, the dedicated double STI levers are less problematic.

petemadoc

Just though I'd say thanks for the help and round this off.

The problem

Simply a slack cable.

ugo.santalucia

It's pretty obvious that the cable needs a bit more tension.

Shift down to the lowest ring, undo the front derailleur screw and tensionthe cablet a little by pulling with your hand. Then tighten the bolt and try shifting up and down. it should work fine.

Afterwards, and only after you've done that, you can adjust the limting screws if needed, just to make sure the chain does not fall off (overshifting) but that is not your current problem.