New cassette, new chain - weird problem

chrisaonabike

Update:

Went out for a little ride tonight - just a quick lap of Richmond Park. Shifting is fine, all feels good. Just catches pedalling backwards still on the smallest cog.

The God of Irony was in the ascendant though - I wasn't pushing at all, just spinning my legs round on Broomfield Hill. This chap comes hurtling past me out of the saddle, pushing a big gear, his chain snaps literally right in front of me, and as he desperately tries to unclip, he fails and falls over in slomo.

So of course I stopped - turned out he had no chain splitter and had never changed a chain - and since I'm now a total expert on all things chain-related (cough, cough), and carry a chain tool and connecting pin (and a quick link now) I gave him one of the pins, reconnected his chain and sent him on his way.

Funny though, me with chain problems.

Old_Timer

Good on you for stopping and helping the rider with the snapped chain, be careful that some of the angry birds here that feel stopping to help another rider unless they are bleeding profusely :shock: don't castigate you, or lat least shun you :roll: .

It sounds like there is a slight tooth problem on the smallest cog, to me. If that is the only cog that's having the issue then maybe you can narrow the problem tooth (teeth?) and hopefully straighten it out.

I kind of miss the old freewheels, with the separate cogs you could customize or replace, from the big Regina or Suntour cog boards in the LBS. Hope that you sort the last bit out easily, Chris.

mamba80

its not only stopping to help a stranded cyclist that will get "police" out, its also a failure to read (twice) that the op has swopped out the offending cog to no avail

refit the old chain just to prove?

chrisaonabike

mamba80 wrote:

refit the old chain just to prove?

Yes, I'm reluctantly getting to that point. It's all mucky though

Old_Timer

mamba80 wrote:

its not only stopping to help a stranded cyclist that will get "police" out, its also a failure to read (twice) that the op has swopped out the offending cog to no avail

refit the old chain just to prove?

Good enough, I failed to read that one, twice as you so warmly point out. My shame is immense and I feel your stern glare of rebuke :oops: , despite your smilie

davidof

Did you tighten the cassette after changing, even if they move only a fraction they can cause the catching you are seeing.

chrisaonabike

davidof wrote:

Did you tighten the cassette after changing, even if they move only a fraction they can cause the catching you are seeing.

There's practically no movement if I pull it and push it. I didn't do it up super-tight, but it felt pretty solid.

davidof

ChrisAOnABike wrote:

davidof wrote:

Did you tighten the cassette after changing, even if they move only a fraction they can cause the catching you are seeing.

There's practically no movement if I pull it and push it. I didn't do it up super-tight, but it felt pretty solid.

ok that sounds good; another thing to rule out. I had a cassette with 1mm of side to side movement, rode ok but caught the chain a bit when you back pedalled.

chrisaonabike

Thanks for all the suggestions, folks. I'm probably going to leave it now, till after RL100 - it rides fine and the shifting is pretty sweet, so I figure messing with it now is probably a bad idea. I'll put the old chain back on after Sunday, see if that changes anything, but obviously if anyone has any more ideas I'm all ears.

Schoie81

I'm not being funny, but if this only happens when you pedal backwards, is there actually a problem? Do you do a lot of pedalling backwards?

I once had what sounds like the same problem as you, but mine was caused by me having installed my connex quicklinks the wrong way around and it happened when pedalling normally. However, you say that yours happens with every rotation of the wheel/cassette and so cannot be the same cause.

chrisaonabike

Schoie81 wrote:

I'm not being funny, but if this only happens when you pedal backwards, is there actually a problem? Do you do a lot of pedalling backwards?

Yes, only when the chain is going backwards. I don't pedal backwards much, obviously (it ruins all my numerous KOMs and makes hills really tricky ). It's just that a chain catching on cogs isn't normal, and a smooth freewheel is expected, I'd have thought, if the gears are indexed right, which they do seem to be.

I once had what sounds like the same problem as you, but mine was caused by me having installed my connex quicklinks the wrong way around and it happened when pedalling normally. However, you say that yours happens with every rotation of the wheel/cassette and so cannot be the same cause.

Yes, exactly.

rjkflyer

ChrisAOnABike wrote:

Ok, here's what it looks like from behind... pretty much bang in line to my eye, let me know if you spot anything obvious. I'll do another from the side...

Why is there exposed gear cable?

If the outer is not under tension then the RD is also not prevented from moving in one direction (away from the limit stop) and therefore when you pedal backwards the RD will float a bit.

chrisaonabike

RJKflyer wrote:

Why is there exposed gear cable?

If the outer is not under tension then the RD is also not prevented from moving in one direction (away from the limit stop) and therefore when you pedal backwards the RD will float a bit.

Good spot, but it was only off to remove the cable tension when I was checking the limit stop, as someone suggested earlier. It catches in the same way whether the cable is on or off.

mamba80

so without labouring the point, with the cable off and you undo the H screw 1/2 a turn what happens to the RD ? it should move out board, beyond the line of the smallest cog.
to me, your RD is very slightly inboard of the cog and as I said earlier, there is 2mm of float on the top jockey wheel, so there is a small amount of error to be had here - ur lbs has straightened the hanger, so it would be normal to have to reset the limit screws.
Indexing has nothing to do with your problem, as it never catches on the 9th or above cogs, and just to be certain, this occurs on big/small, not small/small ?????

rjkflyer

mamba80 wrote:

to me, your RD is very slightly inboard of the cog and as I said earlier, there is 2mm of float on the top jockey wheel, so there is a small amount of error to be had here

I would agree the RD is very slightly inboard.

So, aside double-checking this, swapping the jockey and tensioner wheels can be tried to see if the float in the top one is for some reason causing/exacerbating the problem.

Looking at the pic, I could persuade myself that the upper (jockey) wheel is left of centre - look at the shoulder visible to the right and it is obviously more than the left - down to float as stated.

In a correctly-set system the float serves no useful purpose, in my opinion. I've got an 11-speed Campag system and have fitted ceramic bearing J&T wheels and they have zero float - never had anything other than superb indexing: I'd like to think the float is simply a comfort blanket for those who don't maintain things spot on!

Nairnster

I would agree with Mamba80 in that its not set up as per instructions. Adust the limit so the top jockey wheel is in the correct position relative to the small sprocket ( which I always understood to be slightly to the right as you look from the rear), and then see if you have the problem.

The rear mech is under less chain tension when pedalled back, so it maybe slightly catching. Pedalling forward, there is more tension as the freewheel is engaged and you are driving the wheel. This may be enough to overcome very slight catching.

Got to be worth a try