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The bike is about 10 years old with an average 30KM per week on it so roughly 15,000KM. It is a 3 * 10 speed Deore XT and it has performed great up until recently when my chain broke (bought a Park tool to make sure to check on chain wear).

I have an issue with my chain slipping while staying in the same cog. When my chain broke, I replaced the cassette and I have also replaced the two larger chainrings. The chain was shortened to the same number of links as the last chain. The larger of the new BBB chainrings has 2 more teeth than the original Shimano and the middle BBB chainring is the same size.

What happens is that if I use the smaller cogs on my cassette, the chain appears to slip almost as if it is skipping some of the teeth on the chain. This happens on all 3 front chainrings, but more with the middle and the larger one. The slipping is less likely 5 cogs in from the smallest (fastest) cog, and more frequent when on the smallest cog in the cassette. On 6th cog or larger I haven't had it happen. It is not a loud noise, and almost sounds a bit like a change of gears (without it moving left or right), however after today's ride I noticed some metallic particles that the chain is picking up, so it is definitely adversely affecting the cassette.

It happens while under very little pressure while going down a hill and it also happens when there is a bit of pressure on it. I haven't found it to be as much of an issue under heavy load. Unfortunately it is not persisting all the time. I can get 4-5KM without it having any issues and other times, I can't use 4th smallest cog even without it skipping every couple of rotations of my crank.

Also, a few weeks ago, I noticed that my derailleur bolts fastening it to the frame were very loose before this happened, and I have tightened it to ensure that it is consistent. I was amazed that everything worked as well as it did with one of the bolts being very loose.

I have adjusted the gear lever so the derailleur is perfectly aligned with the cassette cogs.

Any suggestions on what this could be? My guess is the derailleur might be worn or the springs might have weakened. Could it be a link in the chain?

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3 Answers 3

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Are you really sure it’s not jumping to the next cog? Sounds most likely with new parts.

I’d check that:

  • the cassette is correctly installed and tightened (it needs 40Nm tightening torque which is a lot)
  • that all links of the chain move freely, especially where it’s closed (I hope you’ve used a master link or a dedicated closing pin). If you’ve used a closing pin, make sure it’s flush. If it’s a master link, make sure it’s fully closed.
  • that the rear derailleur or derailleur hanger is straight and not bent.

Hang the bicycle somewhere (or put it upside-down), pedal with your hands and closely observe the chain as it moves. Check that everything shifts smoothly and precisely.

If the chain is actually skipping under load it should be much worse on the smallest chainring.

Regarding:

Also, a few weeks ago, I noticed that my deraileur bolts fastening it to the frame were very loose before this happened and I have tightened it to ensure that it is consistent. I was amazed that everything worked as well as it did with one of the bolts being very loose.

I assume you mean the derailleur hanger (which is usually fastened with two bolts)? It’s mainly held on by the rear wheel’s quick release axle which firmly presses it to the frame. Usually you can actually see the derailleur hanger move slightly when you tighten the quick release.

The chain was shortened to the same number of links as the last chain. The larger of the new BBB chainrings has 2 more teeth than the original Shimano

I hope it’s not too short now. Make sure the derailleur is not fully extended when shifting to the biggest cog while on the big chainring.

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  • Related to this: I wonder if the OP’s rear derailer has been adjusted properly. A noise sounding like the chain wants to change gears is one symptom that the RD cable tension is off.
    – Weiwen Ng
    Commented Mar 20, 2021 at 17:40
  • Why does the cassette need so much torque? It seems pretty solid on there once there's a bit of resistance on the lockring, I don't know what NM I'm tightening it to though, 'arm tight with a 10" wrench' if that makes any sense.
    – Wilskt
    Commented Mar 20, 2021 at 17:48
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    @Wilskt: I guess first of all because it mustn’t come loose and the cogs should be stiff and tight. Secondly because the freehub body is often made out of aluminium. The cogs should be mostly held on with friction. If that’s not the case they start to dig into the body. The bigger cogs are often riveted together which could explain why they work for OP.
    – Michael
    Commented Mar 20, 2021 at 18:45
  • I am using a genuine Shimano HG95 chain as well as a CS-M771 cassette. The BBB chainrings were out of necessity as they could not get Shimano chainrings to replace the worn ones. In saying that, the smaller of the 3 is a genuine Shimano which is also slipping. I did use a torque spanner to tighten this one to 40Nm. Thanks for the hint about the chain, I will check that later today. Yes, I did meant he derailleur hanger.
    – Roland Crachi
    Commented Mar 20, 2021 at 22:52
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    The HG95 chain is directional, meaning it only goes on one way. The outer links with stamped markings face the outside. The other side's outer links are entirely devoid of markings and faces the inside, toward the bike. Getting it backwards can cause at least excessive noise and poor shifting. Truly slipping on the cogs would be a stretch for a backward directional chain to cause.
    – Jeff
    Commented Mar 21, 2021 at 22:21
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Below is the chain inside the packet. enter image description here

Below is the back side of the same chain - HG95 with both sides having identical print on them. enter image description here

Thank you to everyone for providing some hints on where to look. It has greatly helped.

Also, to confirm the chain definitely slipped rather than shifted and I found the issue.

The issue was that one of the links in the chain was very stiff which is dissapointing given it was a new Shimano chain.

The picture shows the suspect link with all the weight of 90% of the chain suspended below the link.

I realized that I mentioned it was a HG95 and as it turns out it was a HG54. Now it is a HG95.

enter image description here

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  • Strange. I’ve only had this with closing pins or rusted chains. Try bending the links sideways to loosen them up.
    – Michael
    Commented Mar 21, 2021 at 6:57
  • Yes, I found it strange as well. Given it was a new chain which I lubricated quite well at the time, I didn't suspect it as being a likely issue. I suspect I might have been one of those rare manufacturing flaws. I only went on 2 rides and it seemed to get progressively worse. I will try to loosen it up and perhaps used it as my next chain on the bike. If there are any doubts, I will discard it.
    – Roland Crachi
    Commented Mar 21, 2021 at 21:03
  • Btw: You don’t have to lube a new chain, they come soaked in lubricant from the factory. Usually you can ride several hundred kilometers on the factory lube.
    – Michael
    Commented Mar 22, 2021 at 6:59
  • Does the manual which came with the cassette say something about chain direction? Otherwise it’s really rather strange. The photo at the bottom (with the stuck link) shows HG54 markings. I thought your new chain is HG95? Am confused, but both have “HG-X’ technology, i.e. should be directional.
    – Michael
    Commented Mar 23, 2021 at 11:25
  • @Michael The comment straight above the chain that is jammed mentions that originally I thought I had installed a HG95 but as it turns out it was a HG54, as visible in the jammed chain picture. I had purchased 2 packets of HG95's and while I had originally thought I had used one of them, the first chain which was faulty was a HG54. The one I took the photo of which is still in the packaging is the second packet of the two HG95's. There is no manual with the chain.
    – Roland Crachi
    Commented Mar 27, 2021 at 5:41
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To me it sounds like either they're bad quality chainrings or your freehub is slipping. The freehub can be mistaken for this kind of thing, although it's probably not the culprit if the slipping started at the same time as the drivetrain work.

Over the years I've come to accept the corollary between getting a new drivetrain right the first time and just using Shimano chainrings, especially on their cranks.

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  • But the freewheel slipping should occur on the largest cogs (-> maximum torque), not on the smallest. Unless it’s somehow related to chain angle.
    – Michael
    Commented Mar 20, 2021 at 17:23
  • Thanks for your response. What I didn't mention is that I had swapped out a wheel which also had a new(ish) <50KM casette on it and that had the same behavior. With that I can exclude the cassette and the freehub. I am tempted to take it back to the shop that fitted the BBB chainrings. I must admit that BBB stuff in the past was usually quite good qality and these particular ones spell out compatibility with the Shimano drivetrain.
    – Roland Crachi
    Commented Mar 20, 2021 at 23:02

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