I currently have a Shimano LX M581 9 Speed GS rear mech which i believe is a mid cage. Does anybody know what the max rear tooth capacity the mech can take? Considering going for a 11-36 cassette.

(my PC wont let me access pdf files on the shimano tech docs site, hence asking here)

If it wont work, will a standard long cage MTB mech take a 11-36 cassette?

Cheers

gs is long cage (sgs is super long cage).
Cage length does not affect the max sprocket size ,only the max capacity, which is the sum of the the difference between the largest and smallest sprockets of the front and rear clusters.
It would work if you screwed in the b-tension screw all the way.
The bigger problem you’ll have is 11-36 cassettes are only available in 10 speed,and shimano 10 speed shifters require a dedicated shimano dyna sys rear mech (different actuation ratio).
And sram shifters need sram rear mech.
You can get a 9 speed 12-36 cassettes though.

34t max according to Shimano techdocs.

Tech docs say 28t for an Ultegra rear mech…works ok on the 11-34 on my cx bike (with b-tension screw wound all the way in).
Some things are ‘negotiable’ 😉

Unfortunately, it can also work the other way too. Loads of last years low-end bikes with a mech capacity of 34t wouldn’t clear a much smaller sprocket- guess it’s suck it and see.

Theres only one way to settle this…….
“BIKENERD FIIIIIIIIIIIIIIIIIGGGGGGGGGGGGGGGGGGGGGGHHHHHHHHHHTTTTT” 😀

Naked, and in the stingies of course. 🙂
Wasn’t trying to contradict in my original answer, looked up techdocs with original tab still open,replied, then shut-down and went for tea.