Front Derailleur Adjustment

[Ricd11]

I apologise if this has been asked many times but i've searched the forum and can't find exactly what i am after.

I have a brand new Ridgeback Voyage, but it will not change down to the lowest sproket on the triple chainset. I had a butchers on bicycletutor, and had a fiddle with the adjustment screws on the front derailleur. I was able to get it to shift down to the smallest sproket, however when I went on the middle sproket to test the range of gears the chain started to rub against the derailleur on the top 2/3 gears. I then tried adjusting the upper limit, but I can get no compromise between making the lowest sproket and not rubbing running through all the gears. So i'm stuck at the moment with either no lowest triple or no chain destruction.

The video on bicycle tutor did mention trim, but i don't really know what this is. Also after looking at the bike, the front derailleur seems to be 2-3mm off the largest sproket, where the video states 2mm is advised but the lower the better.

The derailleur is a shimano sora triple apparantly.

Any help would be greatfully received,

Thankyou,
Rich

 

[Fiona N]

Assuming the front derailleur is not bent or broken or stuck in any way, there are basically 2 possibilities for not changing onto the smallest chain ring (I assume this is what you meant by 'sprocket) - either the cable is too tight to allow the derailleur to move far enough inboard (leftwards) or the adjusting screw is screwed too far in thus also limiting the travel inboard. The second point is most easily tested - the video or bike manual should tell you which the lower limit screw is (the left most one, if memory serves) and then, if you unscrew this one (say, a half turn at a time), the derailleur should move left when the change lever is released to the position for the small chainring (least chain tension). If it doesn't, or doesn't move enough to allow the chain to be run onto the small chain ring, then it looks like you need to release some of the cable tension. (Report back and someone will give further instruction).

The trim could be either the height of the derailleur above the big chain ring - there should be a vertical gap of about 2mm between the bottom edge of the outside of the cage and the teeth of the big chain ring when the outside of the cage is directly over the big chain ring (which should be roughly the position for the derailleur with the chain on the middle ring). Or trim could refer to the angle between the outside of the derailleur cage and the big chain ring - modern derailleurs are usually best if these two are parallel. It's not too likely these are far out if the middle/big chainring transfers work OK.

 

[Fiona N]

Belatedly reread your OP - sorry I managed to ignore a whole load of what you wrote.

So, to continue: when the limiting screw is unscrewed to allow the derailleur to move enough inboard to change to the small change ring but then using the small rear sprocket causes the chain to rub on the derailleur in the middle chain ring, it means the cable tension needs a bit of adjustment. In this case, a slightly tighter cable will move the cage outboard so the chain isn't rubbing. However, tightening the cable may mean that you need to release the lower limit screw more too. Eventually you may find that the lower limit screw is fully released so the derailleur can't move any further left with the cable tension as required for clean chain running in the middle chain ring.

In this case, it's worth noting that not all set-ups can be made ideal - it could be that if you want the small chainring to run well, you'll have to miss out on the small sprockets with the middle chainring - you can get these higher gears anyway with the big chain ring and mid sprockets.

 

[I am Spartacus]

http://www.parktool.com/repair/readhowto.asp?id=75

I found the ParkTool guide better for setting up the front derailleur after I replaced the crankset.


Having said that.. if it is brandnew... should you be having the problem?

 

[gwhite]

Better to go to the Parktool website and follow the instructions there. It's also better to start from the beginning as this can be tricky. As opposed to the above post, all sprockets should be available on the middle ring and if not, it's set wrongly. Being a Sora FD this should be easier to set up compared to a road triple.

 

[fossyant]

Don't forget, you should have a little 'trim' available in the middle - i.e. a quick jab on the STI may drop it back enough for the sprockets not to rub, or push it further up (other button) to stop the smaller sprockets rubbing. Remember though, not all sprockets will be usable without rubbing.....

 

[Ricd11]

Thanks everyone, I'll have a butchers at that website tomorrow and give it a go

Rich