Chain jumping straight from small to large chainring.

[Brand X]

Sorry, I know similar questions about derailleurs have been posted a million times, but I can't find a specific guide on how to fix this problem. I recently replaced the crank-set on my bike (it should fit, it was picked for me by a guy who knows what he is doing) but now I can't get the adjustments right on my front derailleur, I started by playing around with the height of the band that holds the front derailleur in place (1mm clearance) and I also played around with the left-right adjustment to stop it rubbing against the chain - unfortunately it does still rub slightly either on one side or the other no matter how I position it.

The main problem is that if I set it so it can go onto the middle ring, it won't go into 3rd gear - the big chain-ring.

I first set the derailleur H and L limiters so that it would go down to the smallest chainring (1st gear): That works. But I cannot make the front derailleur work on both the middle and big chain-rings; it will only work with one or the other. It either jumps straight from smallest chain-ring to biggest chain-ring (1st gear to 3rd gear) or with a bit of fiddling I can make it work in 2nd gear, but then the gear selector is at maximum pull and I can't squeeze the selector trigger on the handlebar any further.

It was working on the old chainrings - although the big ring was shot - but now I seem to have messed it up.

 

[lpretro1]

Start with cable slacked off and set L limit. Attach cable and put in big ring - if it won't go it's cable tension or H limit set down to hard. Slack H limiter screw off - if still wont' go it's cable tension. Adjust tension to shift into big ring & small sprocket then check H limit so it doesn't throw chain off outside

 

[Brand X]

Start with cable slacked off and set L limit. Attach cable and put in big ring - if it won't go it's cable tension or H limit set down to hard. Slack H limiter screw off - if still wont' go it's cable tension. Adjust tension to shift into big ring & small sprocket then check H limit so it doesn't throw chain off outside

Thankyou Ipretro, I'll try that right now.

 

[lpretro1]

It is easier if you have either a barrel adjuster at lever end (if it's mtb type shifter) or an inline shifter for road type (or some bikes have a barrel adjuster on the frame downtube too

 

[Brand X]

Too dark to any more tonight, but I've replaced the gear cable because it was very frayed on the spot where it is held in place. It might have something to do with it or not. I shall have to wait until tomorrow to find out.

 

[Deleted member 1258]

Have a look through this.

http://www.parktool.com/blog/repair-help/front-derailleur-adjustment#article-section-3

 

[boydj]

With a triple, I found that having the 'L' screw as low as possible without causing the chain to drop, and not too much tension in the cable on the low setting is the way to go. A dog fang or similar to prevent the chain falling off on the inside might be useful too if difficulties persist. Changing onto the small ring before you get onto the largest cogs is also good practice.

 

[Brand X]

With a triple, I found that having the 'L' screw as low as possible without causing the chain to drop, and not too much tension in the cable on the low setting is the way to go. A dog fang or similar to prevent the chain falling off on the inside might be useful too if difficulties persist. Changing onto the small ring before you get onto the largest cogs is also good practice.

Thankyou Boyd, that turned out to be a good tip! I followed the ParkTool guide (thanks Dave) and I realized my first mistake was not setting the angle of the derailleur cage correctly; looking along the back of the chain (sort of like looking down the length of a rifle) I immediately saw a textbook example of the chain pulled to one side.
I still had to spend two hours faffing about though; the chain was rubbing and the cage just would not cooperate, but playing with the barrel tensioner on the gearshifter, I've now got it more or less acceptable. It's still rubs a tiny bit, which is probably going to annoy me and it might get worse, but for now it seems to be basically okay.

 

[Deleted member 1258]

Nice to know you've got it sorted.