Bicycle Mechanics - Chain drops when shifting to small ring
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06-15-08, 12:30 PM
Hi guys, I've got a small problem where my chain will sometimes drop when I shift to the inner chainring. It happens about 60% of the time. I have never adjusted the front deraileur before and I am not really sure which limit screw to turn and in which direction. Can anyone help? Thanks.
06-15-08, 12:32 PM
BTW it's an Ultegra deraileur.
06-15-08, 01:10 PM
you need to adjusted the (L) low screw . turn it until the dérailleur,s cage just clear the chain when the bike is in low (smallest) gears combo.
06-15-08, 01:43 PM
Who did adjust your front derailleur?
I'm going to be a little bit contrary, assume the derailleur was adjusted close to right initially, and offer an alternate plan.
1. Shift into your smallest chainring and largest rear cog. Take a look at where the inside of the derailleur cage is located relative to the chain. It should miss the chain by about 1 millimeter, that's pretty darn close.
2. If that's the case, you obviously aren't going to adjust your low limit screw any more because it would cause chain drag.
3. Now shift into your smallest cog in back and gently shift onto your biggest front chainring. If it's hard to shift there's your answer. Loosen your high limit screw about 1/8 turn and that'll fix it.
Oftentimes bike mechanics set the high limit screw by shifting into the hardest gear combination and just adjusting the limit screw against the derailleur. If you do it that way you risk causing the derailleur to bind up when you shift onto the big ring. Then, when you try to shift down, it hesitates initially and, when it overcomes the bind up it throws the chain forceable across the crankset and overshoots the granny gear.
06-15-08, 10:41 PM
You should adjust your derailluer as above, then get a chain watcher. It's a kluge, but it gives you more margin for error. I think not having a chain watcher is the most OCP thing in cycling. Piepans aren't cool though, go figure.
06-15-08, 11:45 PM
Adjust your high and low limit screws as described or see parktool.com for front and rear derailleur adjustment. If the limits are set correctly, you're 90% there.
Next step - Adjust cable tension. The fder spring is constantly applying pressure to bring the fder back towards the seattube. Cable tension controls this. Inadequate tension results in the chain snapping back towards the seattube, sometimes resulting in chain derailment. Increasing chain tension will remedy this. If you have an adjuster on your fder cable, turn it counterclockwise to increase tension. This adjustment is crucial to fine-tune your shifting, allowing up and downshifts to seat properly on the chainrings.
Don't forget to check the height of the fder and the angle of the fder relative to the outer chainring as well. 1-3 mm vertical clearance and parallel or very slightly toed-in for best shifting.
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