At the end of my tether with gear shifting issue

G1032 · 17-10-2022 7:28pm #1

Hi

For a number of months now I've being slowly going mad with a shifting issue on CAAD12. I just want to throw the bike over a wall and never get on it again.

When I am shifting down the rear cassette the chain often comes off the front chainring. I can't fix it. I don't know why it's happening. I don't know when it started other than it was sometime this past summer. I can't pinpoint it to any specific time or work that was done on the bike that might have caused it. I'm going out of my mind with it. It happens on every single ride. I might go an hour and it won't happen but then it could happen 3 times in a minute.

What I've done to try and fix it:

Inner and outer cables changed. Inners changed twice.

Cranks removed and bolts checked. BB serviced twice.

Tried 3 different chains. A KMC, a SRAM and an Ultegra. I took a link off the SRAM one incase it had something to do with chain length. But that definitely made the chain a tad too short.

Indexed about a kazillion times.

Rear derailleur removed, checked, limit screws reset. B screw (or whatever it's called on the R7000) adjusted every which way.

Jockey wheels checked and are perfect.

Tried different wheels and different cassettes.

Shifter seems perfect.

Chainrings not worn by any means.

Tension and Guide pullies line up perfectly.

Hanger not bent and I have verified this with the Park hanger alignment tool. I knew it wasn't bent but verified it anyway.

It can happen at any point along the block. Shifting is smooth otherwise and no issues. Like I said, I could go an hour and it wouldn't happen.

I could not replicate on the work stand for a long long time and then last Friday evening just gone I managed to get it to happen on the stand. I have a photo attached. You can see the chain starting to come off. It always falls to inside. It's not touching the front derailleur when this happens.

Does anyone have any clue what could be causing this? Season is a long way off yet but I simply cannot race on it like this. I will kill myself and/or others.

IMG20221014162937.jpg

cletus · 17-10-2022 7:35pm

I know you've used a number of different chains, but have you always used the same amount of links? Is it possible that you accidentally shortened a chain when fitting, and each subsequent chain is equally too short?

I know it's probably stupid/a long shot, but I can't see anything else

G1032 · 17-10-2022 7:43pm

I shortened the SRAM chain I used but that made that one a tad short. The other chains are the correct length alright. Checked and checked again.

cletus · 17-10-2022 7:48pm

Ok, one last one from me, then I'm stumped too.

I know you checked the cranks, but is there any play at the chain ring? Could the bolts need to be nipped up?

G1032 · 17-10-2022 7:52pm

https://www.boards.ie/discussion/comment/119757589#Comment_119757589

Checked that too at the weekend. I was out on Friday evening and I thought I'd finally figured it out. It must be the chainring is loose. But alas, no such luck. It's spot on.

hesker · 17-10-2022 7:57pm

When it comes off where does the FD end up. Is it in the small ring position or does it remain in the large.

Maybe your problem is with slippage on the front shifter and it’s just coincidental

koutoubia · 17-10-2022 8:06pm

Did you at any point have the chainrings off the spider?

If so it's very possible that the inner chainring is on the wrong way round.

Other than that it sounds like a worn chainring...I know you said they don't look worn. The only real reason imo that a chain can come off the inner ring is that the teeth aren't holding the chain in place . Of course that's presuming that there is sufficient tension on the chain.

standardg60 · 17-10-2022 8:08pm

Does it happen on the inner chainring too OP?

Might look fine but could be encouraging the chain to lift off the cogs

G1032 · 17-10-2022 8:14pm

https://www.boards.ie/discussion/comment/119757622#Comment_119757622

It remains in the big ring position

G1032 · 17-10-2022 8:15pm

https://www.boards.ie/discussion/comment/119757661#Comment_119757661

I had them off a couple of years ago I guess but this only started happening this summer. It's only the big ring it happens on though

G1032 · 17-10-2022 8:16pm

https://www.boards.ie/discussion/comment/119757666#Comment_119757666

It could be. I will take a photo of the chainring so and see what ye all think. It could be worn and me not know it.

Plastik · 17-10-2022 8:17pm

Try putting a different front shifter on. I don't the inner workings of Shimano shifters but I had something similar with Campag ones a few times. What it was with those was the screw holding the tension on the whole shifting mechanism slowly coming loose. A mm or two movement on the FD can be enough to drop it down. Would also be interesting to somehow mark the chain and see if it's happening in the same spot all the time. But if you've tried a few chains, I'd be sticking on a new shifter first.

Is the cadburys Caad a 58?? TAKE MY MONEY

standardg60 · 17-10-2022 8:24pm

https://www.boards.ie/discussion/comment/119757699#Comment_119757699

If it's not happening on the inner then replacing the outer is a cheap obvious try

G1032 · 17-10-2022 8:27pm

IMG20221017201855.jpg

IMG20221017201915.jpg

Just got a text off a mate of mine. Says the same thing happened him before and it was root caused to the tension in three derailleur. Mine seems fine but it's three and a half years old now and nearly 30k km on it. But well looked after and I use another bike for bad winter weather.

koutoubia · 17-10-2022 8:29pm

My money is that outer chainring is worn out. The teeth are letting the chain move when the tension changes and pops up.

standardg60 · 17-10-2022 8:40pm

https://www.boards.ie/discussion/comment/119757742#Comment_119757742

That outer chainring has had it OP, you can clearly see the difference in the peaks and troughs between it and the inner chainring in that second pic

G1032 · 17-10-2022 8:42pm

Super lads. Thanks a million. I'm ordering one now. Added bonus is that I found a 53T 120/90 BCD on Bike24. I didn't think I could get one of those.

gn3dr · 17-10-2022 8:44pm

I'd agree. Hard to tell from a pic but I'd say it is worn or damaged. Some of the teeth look damaged also, like they have taken a hit. Does it spin true with the chain taken off it?

G1032 · 17-10-2022 8:54pm

https://www.boards.ie/discussion/comment/119757834#Comment_119757834

I don't know tbh but new one ordered now anyway. Fingers crossed this will fix it. Jaysus but those FSA rings don't last anything like as long as the Shimano ones.

standardg60 · 17-10-2022 9:02pm

https://www.boards.ie/discussion/comment/119757880#Comment_119757880

I didn't want to say!

hesker · 17-10-2022 9:10pm

https://www.boards.ie/discussion/comment/119757705#Comment_119757705

I suspected the same thing for the very same reason.

But if the FD is staying on the big ring position as OP said this can’t be happening.

I’m just not clear how the chain can get off the big ring without the FD moving inward.

G1032 · 17-10-2022 9:20pm

https://www.boards.ie/discussion/comment/119757965#Comment_119757965

That's what has me flummoxed too. But out on the road I've seen the chain come off the front ring and the FD not moving. It's the very first thing during the summer that I thought was causing the issue but chain would come off with no contact with FD.

G1032 · 17-10-2022 9:22pm

https://www.boards.ie/discussion/comment/119757917#Comment_119757917

🙈. Some pile of rubbish but I would have had to go down the route of a bb adapter to change to Shimano rings so didn't bother. Way too much hassle and God only knows what other problems that would bring.

G1032 · 17-10-2022 10:12pm

Just after thinking of something now. Will the 53T chainring be compatible with the 36T? Isn't there supposed to be a max of 16 between the chainrings?

gn3dr · 17-10-2022 10:41pm

You could maybe drop your FD down a bit also although if you are fitting a 53 it might be close enough

hesker · 17-10-2022 10:43pm

Google wrap capacity and check vs your RD.

Likely only to be a problem if you use small small

G1032 · 18-10-2022 5:20am

Ah I get ya. I won't be using small small. I had always assumed it'd drop the chain on a FD downshift but now the penny has dropped 🤣

G1032 · 18-10-2022 6:51am

https://www.boards.ie/discussion/comment/119758455#Comment_119758455

Am I correct with this? - A 53/36 and 11/28 gives a chain wrap capacity of 17+17 = 34.

R7000 short cage has capacity of 35 so I'm good to go? I never knew about this calculation before.

standardg60 · 18-10-2022 9:03pm

Pics of old chainring v new would be a good exercise OP

hesker · 18-10-2022 10:44pm

https://www.boards.ie/discussion/comment/119759027#Comment_119759027

Looks right to me. But Shimano say max gap in front is 16T. They do tend to be conservative to cater for all range of bikes. I reckon you should be ok unless your bike has particularly short chainstays.

G1032 · 19-10-2022 11:09am

https://www.boards.ie/discussion/comment/119762488#Comment_119762488

I will post these. Ordered new chainring from Bike24 and they are usually 10+ days with delivery.

https://www.boards.ie/discussion/comment/119763020#Comment_119763020

Ya, I'm hoping I will be OK but found a 39T 90 BCD yesterday which I can order if needs be. Would actually prefer the 39T tbh because 36 is far too small really so I might just go ahead and order when I confirm that the current issue is fixed with the new chainring. I don't think I'll ever a 52/36 again.

At the end of my tether with gear shifting issue

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