Front Mech Issue

[lejogger]

Hi All,

This morning on the way to work I dropped from large to small chain ring before a short climb, and as I turned the pedal, I experienced a bit of a jam. I assume this is where the chain catches between the front mech and the teeth of the biggest chain ring?
Either way, there was a jolt, but then it changed fine and I carried on my way...

...Until...

...When I tried to drop out of the big ring again later in the journey, this time it just wouldn't have it. I could see the deraillieur pressing against the chain but not with enough force to push it off.

Now clearly I've damaged something but I don't know what. Have I bent the derailleur? Has it just shifted out of position and can be fixed with a limiter screw adjustment or some cable tweaking.

I'm very crap at gears. Help!

 

[Pauluk]

If it were me I would check the obvious things first. Is the derailleur arm in line/parallel to the line of the bike. Is the derailleur arm at least 2 to 3mm above the chain when on the largest chain ring. Is the cable tension correct. I would have thought unlikely to be caused by the limit screws.

Its difficult to diagnose without seeing the bike, but there are some great videos on youtube showing the setting up of derailleurs, front and rear.

 

[lejogger]

Thanks Paul. I'll check out these things on my lunch break (or before if I can) and report back.

I guess I was just hoping that it may be an obvious quick fix that will make the hills on the ride home a bit easier!

 

[Pauluk]

It still may be. I presume all was working well until today. If so then something must have moved. Have a quick look on youtube at the front derailleur set up if you can.

 

[PpPete]

My bet would be a sticky cable. Disconnect it at the mech end, run some thin oil down between inner cable and outer. Operate the gear shift a few times to move the oil around, then reconnect it. If that improves it temporarily, but it happens again later, time for a new cable.

Whilst disconnected you can check the derailleur cage has enough travel to get the chain easily onto the small ring...it's unlikely to be a limit screw issue, but difficulty in changing from large to small ring makes it even more unlikely to be a cable tension problem IMO.

 

[Scilly Suffolk]

So the derailleur moves freely, but not far enough to change gear?

I would check the cable first: it sounds as if not enough is being pulled.

Short of a catastrophic failure, ie breakage, I doubt the limit screws are either the cause or the solution.

 

[lejogger]

Ah ok.. well there's a bit more to the story - just in case the problem is linked to something else!

Last tuesday I took the bike to Halfords for a service - don't shake your head, they actually did a very good job - well I thought they did. I even posted on here about it!
I rode to work and back on Thurs. Bike felt absoultely great. No shifting problems at all.
So there is a chance that they've messed about with the front mech. They've definitely tightened up the cable I think because the suplus slack now twangs my calf with every pedal stroke when it never used to. But as I said, everything was great on Thurs.

Thursday night however I cycled home in what felt like a monsoon. At one point I could have sworn I was a pedalo. Could it be that everything just got a bit wet and now it's a bit seized up?

 

[Pauluk]

Halfords can be a bit variable when it comes to customer service and mechanic expertise. From what you said about the rain, wouldn't normally be a problem but if the mech wasn't lubricated properly who knows? Definitely worth cleaning and re-lubricating first. Then check the cable to make sure its moving freely. Just bend the surplus tail out of the way when you're done.

 

[lejogger]

Thanks Paul. I guess it's one of those that takes a bit of investigation - and I don't have the time (or the lube etc) to do it in work before cycling home. Good job there's nothing too steep on the way home.
I'm concerned about the chain catching the mech though. I'll take and post a couple of snaps in case you can see anything that's not right.

 

[lejogger]

Attached a side and top view below. I've shifted the mech so that it should be tying to change, but it's staying where it is. Any comments?

...apart from how filthy my drive train is.

 

[Pauluk]

If anything, the derailleur arm looks a bit high. As if its not catching enough of the chain to move it across. Don't know what other people think. Its frustrating not being able to see it working. But if its too high why is it only just started to play up? Is the derailleur mount bolted very tight on the frame or can the mount move? If everything is tight try a quick cable adjustment.


View: http://www.youtube.com/watch?v=1tQxJqGVznM

 

[lejogger]

Ok.. so according to the video - just before 2mins 30 if it won't shift down then I have too much cable tension, and a loosening of the barrel adjuster should sort it out?
I'll obviously double check the positioning of the mount though too.

 

[lejogger]

PS cheers Paul for the vid, your posts and time spent helping.

Thanks everyone for your contributions.

 

[Pauluk]

Be careful, when you say loosening the barrel adjuster. If you turn it out (anti-clockwise) I think you may be increasing the cable tension as you are effectively increasing the distance/path length of the cable. If the adjuster is fully turned in then you will have to undo the cable at the derailleur to decrease the tension. Does this make sense?

 

[lejogger]

Yep. That makes total sense. Clockwise on the barrel. If it wont budge then loosen the cable off from the mech a fraction. Cheers Paul