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I am a newbie at gears. I had to buy a new cassette and back wheel, and have just done a straight swap.

Now I am not getting all my gears at the back. Eg when in fifth gear it says I'm in 4th etc.

What is wrong ?

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    Did you replace the chain? Or are you running a worn chain on a new cassette ?
    – Criggie
    Apr 13 '20 at 0:15
  • You probably need to adjust your derailer. Apr 13 '20 at 1:19
  • Back gears are jumping, that rear wheel's a thumping / Black cycle keeps rolling on past just the same / Old black cycle, keep on rolling / L E D headlight, won't you keep on shining for me! Apr 13 '20 at 1:30
  • (Sorry. This is what happens when you're going stir-crazy.) Apr 13 '20 at 2:18
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When you replace a wheel the cassette is not guaranteed to be in exactly the same place relative to the frame as it was on the old wheel, so you need to re-adjust the limits and indexing of the derailleur. Park Tool has a great instruction page with videos that use can use to learn how to do this.

Also make sure that you cassette is installed properly. Some cassettes have a spacer that must be installed on the freehub before the cassette sprockets.

As Criggie said in a comment, you should replace the chain when you replace the cassette.

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  • That's all double duch to me I kind know what your taking about but knowing my luck I would completely f**k it up Apr 15 '20 at 0:48
  • @christophermcharg High and low limits set how far the derailleur can move inboard and outboard, indexing aligns chain with sprockets. Find the video on the Park Tool page, it explains it really well. Apr 15 '20 at 0:58
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The new replacement wheel is not exactly the same as your original wheel. This means that the cassette is a couple of millimetres sideways from where it would have been positioned on the old wheel.

The rear derailleur is still placing the chain for where the old cassette was.

This is fixable, but can be fiddly. You need to reindex the gears, and probably adjust the two limit screws.

First some terminology: the big cog (easiest gear) we'll call 10, and the smallest/hardest gear we'll call 1. (Some bikes flip this around)

General outline:

  1. Hang your bike up so the rear wheel is clear of the ground, and the pedals can be rotated by hand.
  2. Set the shifter to 1 (hardest gear) and hand-pedal slowly. The chain should be on the smallest cog.
  3. If not, use a screwdriver to adjust the H limit screw until the chain drops into the correct littlest cog.

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You want the chain to sit on the smallest cog at the bottom of its rest.

  1. Then use your left hand to push the derailleur across while slow-pedalling with your right hand. You want to set the L limit screw so the chain doesn't go over the top and jam down by the spokes. You want the chain to barely get to the big cog.
  2. Once both limit screws are set, THEN you should adjust the inner cable.

Adjusting inner cable:

  1. Set the chain on the second smallest cog, and then without pedalling, set the shifter on the number 10.
  2. Use your tools to pull all the inner cable through the pinch bolt on the derailleur, then snug it up.
  3. Slow pedal, and test the shifting. Minor adjustments should be done by turning the barrel adjuster which is probably on the rear of the rear mech.
  4. When its good, tighten up the pinch bolt. If you can't get it running right, redo this section over but make sure the cable outers are in their stops properly.
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    (Possibly dangerous advice for a self-confessed newbie!)
    – Carel
    Apr 13 '20 at 12:13
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    @Carel fair point - there is no shame in getting someone qualified to look at this. Tweaking up gears is probably the second or third-most common problem, with Brake issues being the other, and punctures being always the number 1 problem.
    – Criggie
    Apr 13 '20 at 20:43
  • I would if we were not in lockdown,but halfords is open but would they look at your bike with all this going on Apr 15 '20 at 0:46
  • @christophermcharg I would suggest not put Halford's staff or yourself at risk by making a non-essential trip. Give this a try and have patience. Its fiddly but if you take your time, it should get better.
    – Criggie
    Apr 15 '20 at 1:28

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