Cable tension for front mech

[CAS]

Ok Chaps - time to save this lady's sanity! Is there a foolproof way of getting the cable tension right on a front mech?

I've replaced the cable on the OH's bike - hybrid bike with triple chain ring. I tensioned the cable with chain on the small ring. But on trying to change up it rattles round the middle ring on the first push on the shifter without properly engaging and a second push takes it to the big ring where it rubs the outer plate of the derailleur cage.

I thought I'd got the cable too tight but a bit less tension and it won't move up the chain rings at all.

I've left the limit screws and rotation as before as it seemed to work fine previously.

Suggestions welcome please - I never seem to get front mechs right!

 

[Andy B]

Is the cable clamped on the correct side of the bolt on the mech & routed exactly the same as before?

www.parktool.com has helpful guides to setting up/repairing stuff

 

[D_XZ]

Check the lower limit screw is set so the chain runs fine on the inner ring and largest cassette ring. Next tighten the cable so the mech starts moving as soon as the shifter engages. This should sort it out - then just make sure the upper limit screw is ok.

The screws might not have changed, but thats not to say they were correct in the first place - it may be that only the cable tension was holding the mech in the right place on the innermost position before

 

[FluffyChicken]

... But on trying to change up it rattles round the middle ring on the first push on the shifter without properly engaging and a second push takes it to the big ring where it rubs the outer plate of the derailleur cage.

I thought I'd got the cable too tight but a bit less tension and it won't move up the chain rings at all. ..

That actually sound like you don't have enough tension. It's not shifting far enough.

At the shifter screw the barrel in then out one or half a turn. Then pull the cable through at the mech tight and clamp.
This would give you more often than not an under shift (what you are describing) then keep tightening the barrel till it shift properly up, keep on going till it over shift (doesn't drop back down properly. Keep a mental note of these positions. Now loosen/tighten the barrel between these points until is shifts how you like.
You may need to use the barrel adjust to tweak it while you ride as shifting under chain tension is different to on a stand and the cable and outer may bed in over time.

Another thing I always do is once the cables are fastened down and before tweaking is to tug the inner cable hard to pull all the outers in a little (help bed in initially) Often best to do this on the outer ring if possible.

 

[Anthony]

I agree with all that Ben says above, and it does sound as though you have too little tension.

One additional fiddle that I find helpful is as follows. It helps because I find it hard work to pull on the inner sufficiently hard to get enough tension. Here is the fiddle:

1. with everything disconnected, check that the barrel adjuster on the shifter is a couple of turns out
2. use the rm to put the chain onto the biggest sprocket - it should then of course be 1mm away from the plate of the front mech
3. adjust the low stop until the mech fouls the chain, noting how many turns it took to get there
4. clamp the cable in the normal way, but don’t bother to bust a gut this time
5. re-adjust the low stop, by the same number of turns as before but in the opposite direction
6. step 5 tightens the cable, saving you from having to bust a gut
7. adjust with the barrel adjuster to ensure that the mech is sitting on the stop, 1mm from the chain

This does of course do the same as doing it all with the barrel adjuster, but it does it without using all the scope in the barrel adjuster just to get started. You might need that scope down the line.

And don’t make the mistake I once innocently made. Don’t use any 5mm outer you happen to find lying around. If you ever find any 5mm gear outer, put it in the bin straight away and lock the lid so it can’t get out. Don’t even give it to your worst enemy. You don’t hate them that much.

 

[shovelon]

This is what I do.

1. Turn barrel adjuster on handlebar shifter all the way in.

2. Install new cable.

3. Tension cable and clamp tight.

4. Use barrel adjuster to make derailleur shift into big chainring.

At some point you will run out of adjustment at barrel. So you may need to repeat step 1 thru 4. Really I find no need to mess with high low screws.

 

[CAS]

Thanks chaps - will griy my teeth and have another go and report back. Somehow front mechs cause me more trouble than anything else!

Carol