Bicycle Mechanics - hesitant front derailleur. SLX DEORE.
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Hi helpful people of Bikeforums.
I have a right annoying inexplicable front mech issue that I have failed to get my head round as have all the mechanics at the bike shop I work at. I hope that the wealth of knowledge on here may be able to shine some light on this...
I have recently changed the drive train on my touring bike [a Trek 520] from Shimano 105 chainset and Deore LX rear mech to SLX rear mech and Deore XT front mech with SLX triple chainset.
But much to my chagrin after much tweaking and setting up the mech does not want to shift down from the middle chain ring to the inner chain ring when riding under load [slight hill etc] although it's fine in a bike stand.
The derailleur wobbles and hesitates as if the spring tension is not up to the job before finally snapping [alarmingly] onto the chainring or not at all. I am using Dura Ace bar end shifters which are friction shifters with a new cable.
I swapped out the Deore XT front mech with a SLX front mech today to see if the mech was the cause and it's not made much difference. the shifting is far from smooth and the shifter still wavers.
I would greatly appreciate any input from anyone with some idea of what maybe the problem as I really need to get the bike set up for a tour of China I am planning this Summer.
Pictures can be added if it will help illustrate the set up.
Sounds like the cable might be hanging up somewhere; have you checked to make sure it moves freely?
Also, make sure the cable bead is firmly seated in its hole in the shift lever.
07-13-09, 01:53 PM
Are you still using "road" shifters? The cable pull required for a mountain bike front deraileur is different than for a road derailleur so if you're using shifters indexed for road bikes, you'll need a road front derailleur for it to shift correctly. Even a cheap one will work fine: I use Tiagra with 9-speed tripple mountain bike crankset on my cyclocross bike.
The mountain bike rear derailleur will shift fine with road shifters though (i use one). It's just the front that is different.
Thanks rmfnla, I had thought that but not checked it, just did, the bead is snug and seems to stay exactly where it should.
The cable was greased when inserted so unless there is some other issue with the cable housing it seems like its unlikely to be that. Especially as the shifting is absolutely fine when in a stand and riding on a level surface. It's only happening when shifting on an incline [when the chain is at its taughtest] and only a slight incline and its not intermittent it's every time.
Could there be some kind of issue with chainline?? I did eye up a Cannondale Rush at work that uses SLX with Deore XT front mech and it looked the same chainline although its hard to tell precisely.
I know that these mechs are usually used with rapid fire shifters and friction shifting is less snappy but this shouldn't be the problem??
I am using a DA bar end shifter which is road. This could be it although the front shifter is not indexed. I was told that this should be ok as it is not indexed.
I also was under the impression the 105 road derailleur would need to be replaced as the outboard bb would put the chainrings further out, this is interesting if it's not the case.
07-13-09, 05:42 PM
If the shifter isn't indexed, then you should be able to get it to work. Hope you can find the problem.
07-14-09, 09:25 AM
Remote diagnostic and repair of bicycles is never easy, especially for the kind of difficult problem that has already been examined by live mechanics.
What I suggest is to unscrew the low-limit screw of the FD so that the FD goes a bit further inboard than you think is best. That should increase downshifting performance at the risk of increasing the risk of dropping the chain inboard of the inner chainring. Also, make sure your bar-end shifter allows the cable to become completely slack when the shifter is all the way down.
If it works, you can deal with and stop all chain dropping with a chain guide like the N-Gear Jump Stop (http://www.gvtc.com/%7Engear/).
Don't worry, such an adjustment is very safe once you have a chain guide.
07-14-09, 12:12 PM
Anytime someone is having problems with their FD - at least one-per-day in BF - I end up recommending starting from scratch and uninstalling/re-installing the FD. So this is my 'cut & paste.'
Take the cable off the FD. Now install it from scratch as per Park Tool Repair:
When you have it properly trimmed and are ready for the cable - a new one wouldn't hurt - you want to pull the cable taut - not too tight, taut. Then apply 48 to 60 inch-pounds to the pinch-bolt. Then put it through it's paces.
It's always easier and faster to install a FD from square-one, than it is to make adjustments with it already attached. This tends to fix one thing - while throwing another out of kilter. Start fresh. You'll get it.
07-14-09, 02:31 PM
So, just to be clear, a friction Dura Ace barend WILL work with a mountain FD? I've got a Deore FD on my bike now to keep the chain from dropping off my 1x8 setup, but I'm planning to make it shiftable this week when my crank gets here.
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