Problem with my big ring

[lejogger]

I've had an ongoing shift problem when manouvring between the large and small chain ring on my compact double.
I took it to the shop and they reset the front mech position using the limiter screws and it then shifted fine on the workstand. Back on the road though it's a different story.

The issues are thus:
Small to Large - taking a good few revolutions to pick up. Sometimes the chain will really struggle to get up there, and often when it does, it will tumble over the other side.

Large to Small - frequently, and especially at low speed the chain really doesn't want to leave the big ring.

I've used the barrel adjuster to loosen the cable and make sure the mech cage is central over the chain when in the big ring, but the problems persist.

Does this seem like:
a) I have no idea what I'm doing and it just needs someone to set up the mech properly?
b) It's possibly time for a new cable?
c) Something else?

Cheers for any advice.

 

[Rob3rt]

I have had the small to large issue before and it helped to smoothly push and hold the shifter over until it jumped up to the big ring, not sure if this is normal or not and it wont help with your big to small issue but you could try it for the small to big issue

If the chain is being shipped over the big ring and you are dropping the chain off the other side, then my ignorant opinion is that the limits are off.

 

[lejogger]

If the chain is being shipped over the big ring and you are dropping the chain off the other side, then my ignorant opinion is that the limits are off.

That was my instinct too, but because the limits were reset not too long ago, I was wondering if perhaps it could be a cable issue weakening the limit position.

I have had the small to large issue before and it helped to smoothly push and hold the shifter over until it jumped up to the big ring

I've tried everything to get it to shift... smooth, rough, slow, fast etc. There's definitely a fundamental issue that goes beyond my shifting technique.

It's frustrating because the shifting on my SRAM Rival gruppo on the best bike is always spot on and so effortless. With the Apex i feel like I'm constantly wrestling with it.

 

[Andrew_Culture]

I'll leave the title for Fnar to reply to...

 

[GilesM]

Small to Large - taking a good few revolutions to pick up. Sometimes the chain will really struggle to get up there, and often when it does, it will tumble over the other side.

Sounds like the front mech is just not moving far enough over, and when it finally does, it goes to far, the limit screw should stop the mech moving to far, and if it's not moving far enough (you say it takes a few revs to catch on the big ring), the cable maybe too lose, or your just not moving it far enough, or are you keeping lots of pressure on the chain when change gear, the mech is not powerful enough to move the chain with lots of power still going through the pedals and keeping the chain really tight.

Large to Small - frequently, and especially at low speed the chain really doesn't want to leave the big ring.

Is the mech moving freely enough, the fact that the bike shop set it up ok on the stand suggests it is, again, are you trying to change rings with lots of pressure on the chain.

 

[Rob3rt]

I've tried everything to get it to shift... smooth, rough, slow, fast etc. There's definitely a fundamental issue that goes beyond my shifting technique.

Definitely, that was more of a stop gap/get home suggestion on how to make the best of the worst. I think the cause in my case was not enough tension on the front mech, as it would clang against the seat tube if I shifted the front mech back and forth with the STI while stationary leaving the chain on the bottom ring. I increased the cable tension until it stopped clanging and now the struggle seems to have dissipated. Don't know what to suggest, other than modifying the limit screw and playing with the tension and watching what happens to the problem. I have never indexed the gears so not sure what else to suggest.

 

[mickle]

Answer 'a)' Chris.

Final answer.

 

[lejogger]

Answer 'a)' Chris.

Final answer.

Touché.

I'm a bit of a novice with geary things but here's what I reckon I need to do:

The cable is definitely far too slack. I need to take that up partly by the barrel adjuster (i.e. get that to a neutral setting) but mainly at the mech. Do i do this when in the big ring or the small ring? Does it matter?
This will then make the mech well out, so I will need to reset the limits using the low screw when in the small ring and the high screw when in the big ring.

On track, or way off?

 

[PpPete]

Easier to adjust the cable tension when on the smaller ring
If the limits are set correctly (and I'm not convinced they are from you description) then you do NOT need to reset them just because you altered the cable tension.

Is it a band-on mech? Is it aligned properly? At the right height?

 

[lejogger]

Easier to adjust the cable tension when on the smaller ring
If the limits are set correctly (and I'm not convinced they are from you description) then you do NOT need to reset them just because you altered the cable tension.

Is it a band-on mech? Is it aligned properly? At the right height?

it is a band-on mech yes... I'm pretty sure the height is fine, but it's worth checking when fettling at the weekend.

 

[Cubist]

Couple of things to check, like are the cables, inner and outer in good nick? Is the cage of the mech in line with the rings, and does it sit about 3 to 5mm above the teeth of the outer ring when shifted to it? If all of those are right,, then shift to smaller ring and set the inside limit visually. On big rear cog the chain should miss the inner cage plate by a gnat's cock. Now undo the cable clamp and pull the cable taut so that there is no slack. Now change to big ring, and little rear. Again, set the limit using the screw, so that the outer plate of the cage misses the chain by a midge's dick. In theory that'd sort it, but we all know it'll take a bit.more swearing yet. Shift to the middle rear cog and check for a smooth change between the two chainrings. Here's where the fine adjustment on the barrels will make sure jt shifts up.smoothly, and drops down quickly without shipping. Have a go, you won't break it by fiddling!

 

[lejogger]

Couple of things to check, like are the cables, inner and outer in good nick? Is the cage of the mech in line with the rings, and does it sit about 3 to 5mm above the teeth of the outer ring when shifted to it? If all of those are right,, then shift to smaller ring and set the inside limit visually. On big rear cog the chain should miss the inner cage plate by a gnat's cock. Now undo the cable clamp and pull the cable taut so that there is no slack. Now change to big ring, and little rear. Again, set the limit using the screw, so that the outer plate of the cage misses the chain by a midge's dick. In theory that'd sort it, but we all know it'll take a bit.more swearing yet. Shift to the middle rear cog and check for a smooth change between the two chainrings. Here's where the fine adjustment on the barrels will make sure jt shifts up.smoothly, and drops down quickly without shipping. Have a go, you won't break it by fiddling!

You make it sound very simple, and I wasn't even confused by the highly technical measuring units

I might even have a go tonight, but before rather than after the pub quiz

 

[lejogger]

Just a final thought, I replaced the chain a couple of months back, but rather than counting and removing any links I just slapped the bugger on. Will this have any consequence other than a few chips in the chain stay when on a bumpy road?

 

[byegad]

I'll leave the title for Fnar to reply to...

Waiting with baited breath.

Not wanting to shift big to little sounds like a chain/tooth issue. Are they at all worn?

 

[Cubist]

Yes.:-) The chain needs to be the right length to keep it all taut. Big ring to big ring plus one link is the simplest formula