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My chain keeps skipping loudly. Replacing the cassette and chain had no effect. I also zeroed the derailleur to the 5th gear of the cassette and it shifts smoothly. I have also replaced all ball-bearings and assorted fittings at suspension joints. The freehub seems to work properly. I feel it may be due to frame flex, since I ride a full suspension MTB (poison bikes) and it has noticeable frame flex when pedaling. Undesired gearshifting happens when I turn. I have replaced aluminum washers at the main suspension joint near the bottom bracket several times and this solves the problem for about three months. Has anyone experienced this and have another idea how this can be fixed permanently?

Details: 27 gear MTB, full suspension

UPDATE: Jan 9th: I replaced a washer in the Suspension tightening it up a bit and reducing Frame Flex but the problem persists albeit slightly improved. Based on Responses here I have been watching the chain and noticed that it sometimes bunches up when coasting (not pedalling) -- it seems that the cassette keeps moving despite the pedals being stationary.

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    Another possibility, if there are a lot of miles on this bike, is that a chainring is worn to the point where it's "hooked" and it intermittently grabs and releases the chain.
    – Daniel R Hicks
    Commented Jan 2, 2017 at 23:08
  • Have you replaced the cable? Derailleur springs may be soft.
    – mattnz
    Commented Jan 3, 2017 at 5:59
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    Check gear cables are not getting snagged or too short as you turn the steering - also as the suspension compresses and un-compresses.
    – OraNob
    Commented Jan 3, 2017 at 9:41
  • Can you lock out the suspension? See if that helps for normal road riding?
    – Criggie ♦
    Commented Jan 3, 2017 at 19:28
  • @mattnz: how do I check if the derailleur springs are soft?
    – Mike
    Commented Jan 9, 2017 at 9:37

3 Answers 3

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I had a similar problem with my road bike. I replaced the cassette and it still skipped. I replaced the chain and it still skipped. Finally, I changed the rings and it worked perfectly. The rings looked only slightly worn but I think one or two of the teeth were shortened slightly through excess use. I saved the rings just for a side-by-side comparison with future rings.

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    Yeah, I was beginning to experience skipping in spite of carefully maintaining/replacing chain and cassette when worn. Was on a multi-day ride when this began to get bad, and the ride's mechanic diagnosed it as a worn-out ring. If you watched the chain it would "grab" intermittently as it rolled off the bottom of the ring and this would whiplash back to the rear derailer.
    – Daniel R Hicks
    Commented Jan 3, 2017 at 22:43
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Well, contrary to the advice of 5 bike shops (who I guess were mostly interested in selling me another chain and cassette), i replaced the freewheel assembly and the problem was instantly solved. Bikes shops said "the freewhell is hardly ever the cause" as they rung me up $50 for new a chain and cassette. Glad its fixed and my 10-year old full suspension MTB is back to being awesome. Thanks for all your advice!

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    Just a note, you can accept your own answer.
    – JohnP
    Commented Dec 15, 2017 at 16:50
  • Thank you for the closure - its definitely appreciated. Do please mark this as the Accepted Answer, because its what worked for you. To be fair - you may have needed the chain and cassette anyway, they are standard wear items.
    – Criggie ♦
    Commented Dec 15, 2017 at 21:43
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Just check that the handlebars haven't got spun 360 and got the cables wound round the headset.

Some guy just randomly crashed over his handlebars outside my house without hitting anything and with nothing apparently wrong with his bike. As I was wheeling it away I noticed that when you steered to the left, it pulled the font brake on. What had happened was he'd ridden to the shops, left his bike outside on the floor and as he picked it up spun the handlebars round. Everything worked perfectly but when you steered to the left more than a fraction it caused the cable for the front disc to get tightened just enough to pull the brake on.

As you say it happens when turning, it might be something like this?

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