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Discussion Starter · #1 · (Edited)
I have a new 2021 Trek Marlin 7 with the following drive train spec:

ShifterShimano Deore M4100, 10 speed
Rear derailleurShimano Deore M5120, long cage
*CrankFSA Alpha Drive, 28T steel ring, Boost, 175mm length
Bottom bracketFSA, 73mm, threaded cartridge, 122.5mm spindle
CassetteShimano Deore M4100, 11-46, 10 spee
ChainKMC X10, 10 speed.

The problem I have is that when I change gears from 5th through to 10th, the pedals slip about 1/3 rotation and there is a loud ka-chunk as the chain hammers onto the cassette. The issue is bearable when riding at speeds of up to 10kmh 😆, but at higher speeds, sometimes it's so violent that my feet jump off the pedals. Of course, when moving from a steep incline to a more gentle one, when I change to lower ratio gears, and this happens, I lose all power and rhythm. Very occasionally there is a lovely soft click when changing from 7th to 8th, which is what I imagine to be expected. The gears changing from 10th down to 1st or from 1st up to 5th are perfect.

The shop I bought the bike from insist all that is required is a cable tension adjustment, but this has not made an improvement. I took the bike to an official Trek dealer for a gear set-up. They made adjustments to the cable tension, the derailleur and tightened the cassette (the cassette rocks a little, but I have been told this is normal with a bike in this price range. Though it doesn't seem to be any tighter than it was before the service). They also told me that all Shimano 10 speed set-ups behave like this, and 10 speeds in general; that it is normal, but, although I am not very technically knowledgeable about bikes, I have ridden many over the past 35 years and never had an issue like this which was considered normal and unfixable, especially with a brand new bike. I've ridden about 500km on this bike.

Has anyone advice or similar experiences which have been resolved?

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