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I just bought a 2013 heckler used and found that it ghost shifts under heavy pedaling. I weight 230 so I am probably putting more pressure than average. But this only happens when I have smallest cog in front and largest and 2nd largest in back, fairly common gear ratios for a MTB.

My shifter cable housing runs all the way through to the derailleur and my LBS just changed the cassette and chain. I can physically see my rear wheel shift slightly off center when I apply a lot of pressure to my pedal while keeping the brakes on. I think this is the root cause, but don't know what to actually do about it. I don't think there's any damage to the rear triangle that I can see.

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I'm also wondering if a bent hangar could play a role. I had a branch jam up in my hanger and it ripped it off and snapped the little metal hanger attachment. But I really think the derailment is coming from the top vs from the bottom. As in, I've caught the bike mid skip, and you can see the chain where it leaves the derailleur is in the correct spot, but above it the chain is 3-4 cogs below where it should be.

Any help is appreciated. This issue is sullying an otherwise amazing bike.

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    Are you positive the frame is bending, not the rear wheel is moving in the dropouts? The symptoms would be similar. Did you get a new chain with the new cassette? – Criggie♦ Apr 25 '16 at 20:10
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    Yeah I got a new chain as well. That's a good idea, I'll check to see if maybe the dropouts are moving. thanks – 1mike12 Apr 26 '16 at 16:05
  • Another fix for host shifting is to clean and lube the rear derailleur wire guides under the bottom bracket. If they're not smooth-moving then they can pull the wire for you as the BB moves with frame flex. – Criggie♦ May 7 '16 at 7:35
  • Check also bearing clearance and axle - if it is not broken, bent etc. – krzyski May 17 '16 at 10:22
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Given that the cassette is tied to the axle, if the alignment is changing, you have a few possible causes:

  1. Freewheel is worn out and has a significant wobble
  2. The pivot where the chainstay and frame connect is worn and loose
  3. Axle itself is loose, either through the hub, or at the dropouts

When applying pressure to the pedal with the brake on, it will naturally pull the alignment of the axle so that drive side is further forward than the non-drive side. You also mentioned that the whole wheel moves, so I would lean towards a pivot or axle problem.

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