UKH

I have an old bike with an SRAM X0 9 speed rear mech. Yesterday the cage spring broke. It seems as though this spring is not available/user-replaceable (although the torsion spring is) so a new mech or mech cage will be needed.

The X0 has been the best derailleur I have used so I would like to continue with this system but replacement X0 9 speed derailleurs or cages no longer seem to be available. Could a 10 speed X0 derailleur be used instead? If the cage openings and jockey wheels were too narrow would it be possible to transfer the existing 9 speed jockey wheels and axles from the old mech to rectify this? Is the difference in movement between 9 and 10 speed just in the shifter or also in the derailleur geometry? If the movement is the same and the fittings are transferable I could fix things with a with a new X0 10 speed derailleur or cage. Otherwise it looks like a complete new  (10 speed or more) gear set would be needed if I wanted to retain the same quality.  This would also require new chain, chain rings and cassette: seems a lot to fix a broken spring. 

Another option would be a different type of 9 speed rear mech and, if necessary, shifter. What is there that matches or comes close to the quality of the x0?

Any advice/suggestions

There appears to one here https://www.ridewill.it/p/en/sram-m007515030010-rear-derailleur-x0-3x9-medi...

Shimano 10 speed MTB derraileurs have almost the same cable pull ratio as SRAM 8/9 speed. To get the ratio perfect you’ll have to fit a 6mm spacer under the cable clamp and use a slightly longer screw. I’ve been using an SLX derraileur with my SRAM shifters for years and it  shifts beautifully, if you want something fancier It is still possible to find XT ones on sale.

Thanks for that: I'll try it. I did do a Google search and several suppliers offered them but then had no stock available when I looked into it so I guess I gave up too soon.

That offers another way out but apart from the shifters I would still need to convert the rest of the drive chain from 9 speed to 10 speed wouldn't I?

No, you can keep you 9 speed chain, cassette, chain rings and shifters, you only have to change the derraileur. 

Oddly I was looking at XOs on ebay today (though I was looking for jockey wheels for an XO rather than a complete mech), so not a problem to pick one up secondhand one. 

I have it on good authority (the distributors rep) that Sunrace 9 Speed uses SRAM 1:1 cable pull with the distinct advantage that they are also one of the few 9 speed clutch derailleurs on the market. If you are still looking in a couple of weeks time I may be able to get one for you.

Just checked the cable actuation ratio for shimano and their 11 speed mtb is the same as the 1:1 SRAM used for 7/8/9 speed. So you wouldn’t need to use the 6mm spacer like I am using with a 20spd mech.

A 20 speed mech? Wow!!! 

I liked the X0 so have ordered one from the source suggested by Sir Chasm (albeit at great cost).

As a stopgap I transferred a Shimano Deore/xt setup to my good bike (12 years old) from an even older bike. When I tried it this afternoon to check the indexing it reminded me why I like the X0: the well known difference really. The 1:1 ratio and, I think, rather stronger cage spring give very quick shifting which I like and find useful if you go round a corner "on sight" and get a surprise about what is ahead.

I looked at the photos of some second hand X0s on ebay but they all looked pretty battered to me.

Thanks for all the responses.

I will be trying the Sunrace mech soon as I will convert my 10x2 1998 GT avalanch to a 10x1 so want a clutch derailleur - if it works I have a 1992 Marin Muirwoods which I might put a 9x1 on... I'll let you know how it goes...