Chain catching on front derailleur

[fraz101]

Bit of a strange one for me here and unsure the cause.

Only happens occasionally, when dropping from big to small on front chain rings the chain seems to get caught up and I cannot continue to pedal as the chain seems to be caught, if I did try and pedal through it I suspect I would damage something.

I have to stop pedalling momentarily and pedal backwards slightly for it to correct.

Shifting is generally perfect in all gears, chain isn't stretched and front mech is adjusted fine and springs lubricated well and moves freely.

I realise I haven’t explained it very well but maybe someone knows what I mean!

 

[Deleted member 1258]

Sounds like chain suck.

 

[Deleted member 1258]

 

[Ming the Merciless]

Or stiff link but what you posted ^^^^ more likely.

 

[fraz101]

Thanks and yes it seems more than likely it is that.

I think maybe sometimes I’m late in shifting down approaching hills. Its only happened twice in the last couple weeks having done nearly 300miles.

 

[Once a Wheeler]

I have had this problem when the spacers between the rings were not quite right: a bit too thick, a bit too thin or not fully tightened after a thorough clean.

 

[Deleted member 1258]

Thanks and yes it seems more than likely it is that.

I think maybe sometimes I’m late in shifting down approaching hills. Its only happened twice in the last couple weeks having done nearly 300miles.

I did that a couple of times just after I got my Eastway, one morning I ended up on the floor looking up at the approaching horse and rider, who was looking concerned, fortunately only my pride was dented.

 

[presta]

That's similar to a problem I had, it might be the same cause.

When I changed from middle to large ring, very rarely there would be an almighty crash as it changed. It only occurred every 700 miles or so, but I eventually managed to stop pedalling in time and catch it in the act. What was happening was the chain was going through the gap between the chainring and the derailleur, and the reason that it was so rare (apart from the fact that I don't use the large ring a lot) is that it only occurred when the split link coincided with one of the teeth that have a rounded-off tip. (There are three or four teeth on large chainrings that are trimmed down to allow the chain to slip on and off more easily.)

Shimano allow a range of 1-3mm for the gap between the derailleur plate and the tips of the teeth, but most of this 2mm allowance is used up by tolerances: by the time you allow for different height teeth, chainring eccentricity, and backlash in the mechanism, there's nothing left over to absorb any maladjustment.

The first time it happened was after I dismantled the bike for maintenance, and although I'd refitted the derailleur into the groove it had left in the paint, that still wasn't accurate enough: I had to shift it down by a fraction of a millimetre. The second time was after I fitted a complete new transmission, same problem, same fix: shift the mech down ~0.5mm.

 

[CXRAndy]

Or stiff link but what you posted ^^^^ more likely.

This replace chain for new

 

[Ajax Bay]

This replace chain for new

Not clear whether Andy's "this" is a stiff link or chain suck. Assuming the chain's not filthy (remember this is fraz's bike so no chance) the latter will not be solved by a 'new chain' - in fact might make it worse!
[See this 'chain suck' thread https://www.cyclechat.net/threads/p...-when-in-the-small-gears.269738/#post-6228182 ]
A 'stiff link' is best sorted by finding it and giving it a good 'manipulation' with directed lube a bonus. "new chain" seems a blunderbuss approach.