Chain slipping in highest gear Trek Rail 5

[VOOBOY]

Hi guys, can anyone advise please, my chain has started to slip in the highest gear under heavy load. It's only the smallest cog, no other

NX rear cassette all nice and tight
GX mech not bent
GX chain
Gears all index fine up and down
Limit screws are set perfect
B tension set correctly

All the above are 2 months old so nothing is worn

It's puzzling me at the moment so any help appreciated

 

[Hamina]

When my Rail 5 freewheel started to surrender it had same symptons. It had so much play that you could feel it by moving the cassette.

Trek Rail 5 2020 - Rearhub service

After 500km the rearhub of my Rail 5 seems to come to an end. Problems started when chain started to drop off from front sprocket. OEM SRAM SX chain was at 0,5% -> replaced with GX chain. OEM SRAM SX cassette was missing one tooth -> replaced with new SRAM NX cassette. With new (and old) NX...

www.emtbforums.com

Could be still something else. Just my internet guessing.

 

[VOOBOY]

When my Rail 5 freewheel started to surrender it had same symptons. It had so much play that you could feel it by moving the cassette.

Trek Rail 5 2020 - Rearhub service

After 500km the rearhub of my Rail 5 seems to come to an end. Problems started when chain started to drop off from front sprocket. OEM SRAM SX chain was at 0,5% -> replaced with GX chain. OEM SRAM SX cassette was missing one tooth -> replaced with new SRAM NX cassette. With new (and old) NX...

www.emtbforums.com

Could be still something else.
I'll do some further investigations