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Got a weird thing going on with my rear mech/chain setup... whilst seated on the bike and riding along, if I stop pedalling or pedal backwards, the mech and chain loses tension completely (the mech arm swings forward towards the chainstay). However, if I jump off the bike and flip it over and do the same thing (eg. pedal backwards), everything is fine, the mech keeps tension and behaves perfectly... weird eh??
Any ideas on what's going on? Why does having weight on the rear wheel seem to be causing this? It's an older M975 Deore XT jobbie btw...
Sounds more like a freehub/hub problem to me. Could be that adding load to the bike is causing the freehub to drag more making the chain go slack. Check the cones and/or the freehub bearings.
Definatly sounds like the freehub to me too. What hub is it?
hmm I have something similar. What is the best way to check a freehub that feels fine with no load?
Put another wheel in?
assuming one has one.....but yeah that would be the glaringly obvious solution (slaps head)
What hub is it?
It's an older Mavic Crosslands wheel, so a mavic crosslands hub.
The problem is happening when I take load off the freehub, but it's not being replicated when I flip the bike over to see what's going on, seems odd to me?
What I mean is that you loading the hub via the axle, by sitting on the bike sounds like it might be adding drag to the bearings in the freehub or hub itself and causing the problem you describe hence checking hub and freehub bearings to see if there is any play. Could also be a damaged axle through the hub causing a similar issue.
Ah, I see, thanks for explaining that. Sounds perfectly reasonable to me... now, how do I check these bearings? 🙂
Is there any side to side play in the wheel when mounted in the bike? If you remove the wheel can you wobble the cassette in relation to the wheel?
Try those two first and see what happens.
A lot of Mavic hubs use a nylon bush rather than a bearing in the back (towards the centre of the hub) which can wear pretty quickly and cause play.