Perplexing FD issue
 

I'm having a frustrating problem with a bike I otherwise love: I am unable to downshift from the big ring to the small ring in front, when I'm riding uphill.

On a long hilly ride last weekend, the problem seemed to get worse over the course of the day. If I tried to downshift on even the slightest incline, The FD would grind uselessly against the chain on the big ring.

I had to downshift before I needed to, often crossing my chain, when approaching an incline.

The FD seems adjusted correctly in other respects. The inner and outer limits are where they should be, cable tension seems correct, etc.

Any suggestions? Thanks ...

What kind of shifters and dérailleur are you using?

When I've had that problem, I adjust the FD stop to allow for a bit of overshifting on to the small ring in front--not too much because you'll drive the chain right off of the ring, but just enough. But you might also check to see how the FD aligns relative to the chainrings and check to see if the FD clamp (assuming it's a clamp-on) bolt is tight.

Neal

I'm intrigued by the fact that the problem got progressively worse as you rode. Something is changing.

--I'm guessing dirt was getting into the pivot points or cable guide, preventing the spring from pulling the cage back far enough. If so, maybe all it needs is lubrication and manipulation (move it back and forth several times to work in the new oil). You may have to lube every moving part of the whole system--the shifter, cable, cable guide (or housing, or whatever you have, and of course the derailleur...

--Less likely... perhaps road vibration has turned the adjusting screw?

--Even less likely... perhaps every time you upshift, the cable tension was pulling the whole derailleur down the seat tube a tiny bit, or twisting it around the seat tube a bit ? If so, put it back where it started and tighten it a little more. If this was happening, you'd have trouble upshifting, not downshifting, unless you have one of those backwards Suntour fd's.

--

If I was a betting man, I'd bet that this problem is being caused by your shifting technique.

You said that your derailleurs are adjusted correctly and that it only happens when you're riding uphill. It's your technique... I'd bet the chickens on it... and here's why:

When you pedal, your bike's drive chain has a span of chain that is under tension... the top span... and a span of chain that is relatively slack... the bottom span. And your derailleurs shift gears by moving different parts of the chain... the front derailleur moves the top span of chain and the rear derailleur moves the bottom span of chain.

Because the bottom span is never under tension (well... no tension beyond the tension that your derailleur springs apply) you can shift rear cogs even while you're cranking and grinding on the pedals. The rear derailleur can move that chain any time because the bottom span never gets tight.

But the front derailleur is different. It has to move that top span, and when you're grinding away up a hill... that span of chain quickly gets pulled under such tension that the FD can't make the chain hop chainrings. This is especially true when you're grinding up a hill and suddenly realize that a cadence of 30 rpm isn't the easiest to push. Heck... if your FD has weak springs in it, the least little hill can put you into a situation in which you're trying to shift the FD while putting pressure on the pedals and it just won't go. Does it shift as soon as you let up on the pedals and let them spin for a couple of revolutions?

Try shifting while spinning the cranks under no pressure... I'll bet the problem goes away.

As far as the problem worsening over the day:
Riders tend to let their cadence drop as they tire over the day, and I'll bet that you were tending to grind a little bit lower cadences as you approached those hills. So before you really started climbing the hill, it put you right in the chain tension situation that I described.

The problem did get worse, but probably not because of any mechanical issue.

+1. Back off on your pedal pressure just before you shift.

Used to be that all rear shifts were to be done while freewheeling (at least that is the way I was taught). Then uniglide and hyperglide made it easy to shift under pressure and we
forget the old instructions ;).

I wonder if flexing of the frame at the bottom bracket while climbing hills may be to blame; the setup works fine unloaded; but the slight amount of sideways flexing is enough to throw the limits off.

Hmm, thanks for the helpful ideas and suggestions - in no particular order:

- the FD is a Campy Chorus braze-on double, got it used, not sure how old probably 2000 or newer.

- the front shifter is Campy Record Ergo style shifter, also got it used, not sure how old but it seems pretty recent.

- The frame is ti so I don't think there's much flex happening there. But the cranks are alloy Veloce compact and the FD has some play in the cage (i.e. grab the cage between thumb and forefinger, and you can wiggle it a little, despite it being firmly bolted to the FD braze-on). So maybe there is some flex going on with the FD cage and the crankset.

- I may have bad shifting technique, but not sure how to fix for this issue ... I was reaching a "kitchen sink" situation of trying absolutely everything to downshift - pedal fast, slow, stop, start, more pressure, less pressure, keep changing it up until the darn thing shifted in front. What sometimes helped the front finally downshift was, if I radically crossed the chain by shifting the rear to the biggest/innermost cog while the front was still on the big ring, with the FD grinding against it.

- "Try shifting while spinning the cranks under no pressure... I'll bet the problem goes away." Yes, exactly. On the bike stand, or going fast, or cruising on level ground, it shifts flawlessly.

- "if your FD has weak springs in it, the least little hill can put you into a situation in which you're trying to shift the FD while putting pressure on the pedals and it just won't go. Does it shift as soon as you let up on the pedals and let them spin for a couple of revolutions?" Um, hard to say. The FD's failure to shift only occurs on uphills, when I'm going slow and I don't have much margin to let up on pedal pressure.

- Somehow I think "weak springs" is on the money. If the springs were stronger, this would not happen, right? Does FD spring tension descrease as the FD ages? Do I simply need a newer FD with higher spring tension?

That sounds to me like you need to back off the inside limit screw just a tiny bit. Try riding uphill again, and repeat until you find that "sweet spot" where it shifts correctly without throwing the chain off to the inside. Test at both ranges in the back; both uphill and "zero load" on level ground.

I have an old Huffy MTB that I use to pull my son's trailer bike. We don't go very fast, and sometimes I have to change gears going uphill slugging along at low speeds.

What has impressed me is the fact that the cheap Falcon FD and RD shift fine under load both front and back. Like others mentioned; I had always heard you should back off a touch when shifting; that isn't possible with our "tractor trailer"; but it shifts fine anyway. Maybe its the steel cogs that don't flex? At times; I wish the nicer setup on my Viscount shifted as well.

-James

Tinkered with the bike this morning. I backed off the inside limit screw quite a bit (there is a chain watcher in place, so hopefully throwing the chain of on the inside is not a concern)

Also took up cable slack since the cable may have stretched since I installed it new this winter.

It's not intuitive to me why these would help since (provided you're not at the inner limit) the downshifting power in the FD comes from the spring, not the cable.

But I'd like to be wrong - I'll ride it to work as soon as we have a day w/o rain in the forecast - we'll see!

test rode today - no improvement :mad:

if you have the right bottom bracket, you should be able to adjust your FD (remove the cable first) so that it works on the small ring. you might need to adjust it so it overshifts to the lower gear. you just need need to shift slowly, then trim back if necessary.

Update:

Thanks for the suggestions everyone.

I kept playing around with the FD cable tension and limit screws settings. Nothing was helping.

Then on Sunday morning after another round of tweaks, I tightened the FD cable bolt, and the bolt hole at the top of the FD snapped right off. Doh!

Did I overtighten? Was the FD failing, and was that the cause of the shifting problem?

I bought a new Campy Centaur FD on ebay (old one was Chorus), currently being shipped.

Will the shifting issue disappear with a new FD? To be continued ...

Sounds to me like your cabling is buggered at the Ergo body.

?? I don't follow. please explain?

Here for your amusement is a photo of this FAIL:

http://i170.photobucket.com/albums/u...Derailleur.jpg

+2 on shifting under pressure.

Still getting caught up on changes with new stuff but I guess I just learned the old school way. I know rear derailleurs have changed and there are cogs that shift under pressure now, but I am not seeing similar changes in front derailleurs and how they work.

I am so anal about NOT shifting under pressure that if I do let myself get into such a situation (for example I have to slam on the brakes) I will just get off the bike, pick up the rear and shift it that way.

If the housing is not squared off properly, or seated properly or if the Ergo is too high on the bars it can cause the symptoms you are having.

Start at the Ergolever and consider the routing/position of the housing.

Well OFG you've got me intrigued. But this problem was not happening before, and then it started happening. So if it's a housing seating/routing issue, that would suggest the housing was seated/routed OK and then settled badly after some use. I'm puzzled but I can look into that.

Also intrigued because I did position the Ergos kind of high on the bars, which I seem to need for a comfortable fit. (photo)

But I am stumped as to why that would have an effect on FD shifting like this. Can you share more on that?

There was a thread a few months ago on another forum where that was the problem. That fellow with the problem was in Madison as well. His LBS solved the problem. Which shop in Madison is the best for Campy? His cables had deformed and the Ergos were at a position where the cable couldn't move smoothly.

Ha! Got a Campy front mech just like that! Was having the same kind of problem, thought I'd adjust the cable, tightened the bolt carefully but it just came off in my hand. I replaced mine with a Centaur too, no further problems. I reckon the arm was weakened, maybe from having been dropped at some time and was flexing/bending under use so that the tension didn't release when the cable was slackened by changing down. Has anyone else had one break in the same way? Mine was a Mirage, but looks the same as your older Chorus - probably the same mech design moved down the range? Could there be a design fault or duff batch of castings from Campagnolo?

Interesting ... I'd like to check out that thread if you can point me to it. I'm not sure which LBS in Madison is best for Campy. I shop at the west side Trek Store (since I get Trek Store credit from the charity ride in my signature) which is not a big Campy zone. The wrenches there seem great, but I try to do my own wrenching at home.

Very interesting ... first I'll put on the new FD and see if the shifting issue persists. If it does, then I'll look into the cable housing/Ergo positioning thing.

How much of a gap is there between the tip of the chainring teeth, and the outside flange of the FD - at it's smallest distance?

I try to position FDs as low as possible without touching the big ring - 1-2mm gap