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Last summer it come to light that my bike is suffering extremely bad chain slip, to the extent I feel it is unsafe. From what I can tell, it only happens in the 50t ring, and the 34 may be ok, but it's been a while since I've been on this particular bike, so I'd have to verify.

Near come off the bike a few times moving off from a stop if I was pedalling out of the saddle, so I got a chain checker and I noticed that it was badly worn; the tool slipped right into 1% and who knows how long it was like that given my attitude to use things until they break. Maybe 10-15k miles on the chain. It didn't fix it. So I installed new cassette on there 100-200 miles later, and again, it unfortunately, didn't fix it.

I've reassessed the chain length, and this seems O.K. from what I can gauge (big-big combo - chain has good tension, and I'm not quite able to turn 2 links back on each other to make a Z, indicating that the chain is probably the right length), so now I've reached somewhat of a brick wall. I can't keep throwing money at the thing, especially considering my next step would be to replace the large chainring, but given the cost of FC-9000, it would be quite annoying if it were not to work. Is this a likely fix?

A friend suggested sticky pawls, but when I shoved a club mates disc wheel & cassette on there, I had the same thing, so that probably rules out the possibility of the freehub assembly going bad.

If there is anyone out there with ideas/advice then it would be greatly appreciated. I can get high-resolution photos of the teeth/drivetrain condition if it helps.

EDIT; just shoved it in the workstand and noticed the rear gears were very hesitant to go 25>28 in the big ring & adjusted accordingly. I could've sworn I indexed the thing when I last used it though. If that is the case could this add new cables and a blob of marine grease to the RD springs to the list of culprits?

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Factory new: enter image description here

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  • It's not 100% clear if you replaced the chain before you installed the new cassette. If not, you're just grinding away both the new cassette and the chainrings. At that point of wear, cassette, chain and chainrings should have been replaced all together, otherwise you're accelerating wear on the new parts.
    – aBrav
    Commented Apr 10, 2020 at 15:21
  • I read it as replacing the chain then 100-200 miles later changed the cassette, but it doesn't actually say that you replaced the chain, explicitly. It is best to change the chain when you have a cassette, but I think this 100-200 miles is pretty close to the same time. any accelerated wear is minimal
    – Swifty
    Commented Apr 10, 2020 at 15:44
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    Yes I replaced the chain, and then the casette after I figured out it wasn't helping the problem. From recorded ride data, I can gather I done around 130 or 140 miles between changing the chain and changing the casette. I assume this is not enough time to warranta full replacement of both again as a result of excessive wear.
    – Dan M
    Commented Apr 10, 2020 at 16:30
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    Are you sure it’s actually slipping/skipping or maybe trying to move to a different gear? Make sure your derailleurs are adjusted properly and you are 100% in a gear and not somewhere between gears.
    – Michael
    Commented Sep 7, 2020 at 17:28
  • Now that the question is active again, for 11s systems (the OP indicated he's on the first generation of 11s Dura Ace), users should replace the chain at 0.5% wear. This will enable you to get at least one cassette out of the chain (but the ti cogs on a DA cassette will die quite fast, so run an Ultegra). 0.75% will generally kill even an Ultegra cassette along with the chain, not to mention the chainrings. The figures for 10s systems and earlier are 0.75% and 1%. Running stuff until everything is toast may make sense on Tiagra, but it can't be recommended otherwise.
    – Weiwen Ng
    Commented Sep 7, 2020 at 19:32

1 Answer 1

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Does the large chainring show much wear? I don't think it is the culprit but it needs replacing when it is worn. If the old chain was very worn like that it could have caused wear here too. You could think about chain suck but IME this is quite violent and it jams up the drive by pulling back on the chain; if you look for it you can tell when its chain suck. Check it out, but to rule it out.

As you say the problem is bad moving off from a stop, I would strongly suspect the pawls of the freewheel mechanism in your hub as this is when torque is high on the cassette. I've had the same problem before, it's pretty terrifying when the pedals slip and you lose your balance in traffic. I had mine replaced and instant fix.

You did explore this with club mate's wheel, but I would be pursuing it again with another different wheel and you should at least get into the hub and clean, inspect, grease. Check the wear on the rim and see if it isn't time for a new wheel anyway, otherwise check out the cost of replacing the freehub. You've done the chain and cassette, good, but now you need to take it further.

I think (from reading your post) you can judge the indexing and RD behaviour competently enough and this problem isn't super common despite all noisy, badly adjusted, worn out drive trains there are in the world.

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  • Good video of the freehub slipping here: bicycles.stackexchange.com/questions/56137/…
    – Swifty
    Commented Apr 10, 2020 at 15:40
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    I've always found it a little difficult to gauge how worn the chainring is, but I wouldn't say it is too bad, some of the teeth have become a little rounded but don't seem sharply pointed or hooked. Full res images of my chainset here: imgur.com/a/JeDcWVr Image of factory FC-9000 50T for reference: bit.ly/2VgsVmd I do still have suspicions regarding the pawls. A LBS couldn't get the freehub off the wheels (Fulcrum Racing Sport). I'm sure I've heard of people having trouble getting them off or replacing them on this wheel before; it may be a case of straight swap...
    – Dan M
    Commented Apr 10, 2020 at 16:11
  • ...as I'm not that sure they can be disassembled for inspection.
    – Dan M
    Commented Apr 10, 2020 at 16:12
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    Since the problem only occurs on the big chainring I doubt it’s a freewheel problem. Smaller chainring on the largest cog has much more torque.
    – Michael
    Commented Sep 7, 2020 at 17:26
  • Possibly a stiff chain link. This can occur with a new chain when you use a chain tool. One test is to put on the large ring and the smallest cog in the back, and spin the crank backwards. A stiff link can be seen as it passes through the RD jockey wheels. If a stiff link is found, flex the chain back and forth to loosen it.
    – P. Barney
    Commented Sep 7, 2020 at 19:33

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