Bicycle Mechanics - Ultegra front derailer too strong?
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I recently bought two used road bikes (for very good prices), one of them is full Ultegra (9 speed triple from 2004) but its front derailer seems to be too strong. To shift from the small chainring to the larger ones, it takes a considerable amount of force on the lever. The other bike has a 105 FD/shifter (10 speed triple from 2008) and it is normal, I don't struggle with it.
I thought at first it was the cable and housing, but if I force the derailer into the high chainring position and keep it there with a screw driver, which removes the tension from the shift cable, then the shifter moves easily, suggesting that the cable/housing is fine. The derailer really wants to shift into the smaller cog, so I feel that the spring is way too strong. Also it is a little touchy when shifting from the large cog to the middle cog, it often just skips the middle and goes to the small one due to the spring (and then you have to shift back up to get to the middle). I've also tried cleaning it out with degreaser and regreasing it, but to no effect. Does anyone have any ideas about this issue?
And apologies if this is already addressed, could not find in the search.
My first guess is that the FD isn't positioned perfectly in terms of height and alignment. Check those first.
Assuming the FD position is spot on, I'll bet that your problem is related to cable friction. Shift back to the inner and try shifting by drawing the wire away from the downtube like a bowstring. See if you can get it ro shift smoothly with fairly even force. If it works that way, your problem is in the shifter to frame housing loop, or the shifter itself. It could also be bad ferrules which let the housing squeeze partway through binding the wire.
I looked at the FD, it looks positioned well, small clearance over the large chain ring and it is parallel with the chain. I tried pulling on the cable and it takes a bit of force to manually shift it. On the other bike, it does not take as much force. This leads me to believe it is a problem in the derailer itself...
07-16-11, 02:31 PM
lube the pivots
There's enough lube on it to drown a small cat :\
I think the FD just needs to be overhauled or tweaked or something. In some derailers like the XTR rear one, you can change the spring stiffness, I wonder if it's possible on this one.
Shift onto the smallest cog and chainwheel, and then disconnect the cable from the derailleur. Holding the loose cable-end taut in one hand, actuate the shifter -- the cable should move smoothly and easily in both directions. If the movement is stiff or uneven then completely remove the cable and look for frayed or bent sections. If the cable is damaged replace it; otherwise clean it thoroughly and *lightly* oil it. If the shifter is difficult to actuate even with the cable removed, it will most likely need replacement.
Still with the cable disconnected, unhook the chain from the chainwheel so that it hangs loose. You should be able to move the derailleur back and forth with moderate finger pressure (push on the cable attachment point, not the chain-cage). If the derailleur is stiff or doesn't move smoothly, remove it for inspection. If it doesn't seem badly damaged clean it thoroughly until it moves nicely again, and then lightly grease the pivots.
07-16-11, 06:37 PM
I once solved a similar problem by replacing the plastic cable guide that's mounted below the bottom bracket. It was badly grooved and seemed to "grab" the shifter cable, especially as a ride progressed.
Looking at the bottom of the bike, this one has a metal guide on it. It looks like the cable is not smoothly leaving it, so this could be causing the additional tension. I'll have to find a replacement and see if it solves the problem (dousing it with lube didn't help).
07-16-11, 10:24 PM
If I suspect a seized-up FD, I wear some gloves and manually pivot with my hand. If the spring force is reasonable, it can't be the FD. I may be the leverage point where the cable is clamped. A small error can reduce moment-arm considerably and so the pivot takes much more torque at the shifter.
07-16-11, 11:56 PM
Older Shimano FDs had different pulls than now. If the upper lever arm on the new derailleur is considerably shorter than the new one, there's your problem.
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