Hi All,

This morning on my way to work suddenly the rear mech (10 speed XT, older non-clutch version) stopped picking up the chain’s slack and it does not return to its position when changing to a smaller sprocket – when it stretches to reach the large ones, it says stretched when going “down” (and the chain hangs down nicely, like on a Christmas tree…).

I barely made it to work on time…

Is this easily repairable on lunchtime, or time for a new mech?

If it’s sticking on the bolt that attaches it to the frame then you can strip clean and lube it
But not a job to rush if you’ve not had one apart before

https://www.paul-lange.de/tradepro/shop/artikel/docs/Explosionszeichnungen/SHIMANO/RD_M771_2706.pdf

But not a job to rush if you’ve not had one apart before

https://www.paul-lange.de/tradepro/shop/artikel/docs/Explosionszeichnungen/SHIMANO/RD_M771_2706.pdf
New mech it is then… 😆

I had what sounds like a similar problem with my SLX rear mech recently. Took it apart and the chain tension spring/P-tension spring (Part no. 7 in the diagram linked above) was a deformed, rusted mess.
Managed to source a replacement spring from SJS Cycles.