Wanted B-Tension Spring for RD-M953

N_Spaar

Dirt Disciple
Hi all,

Quite specific request but the B-Tension spring in my RD-M953 XTR derailleur is not functioning properly anymore so I can't use my biggest gear without chain skip.
Does anyone have a spare / know anywhere which might still have one?

Article Number:
Y-53N12000

Thanks!
 
Have you taken it all apart and cleaned and serviced the assembly?

It's hard to think the spring has lost tension, it ought to be well within its fatigue limit and capable of endless operation.
I'm not sure that this is the root of the problem either.

I assume when dérailleurs no longer drop into top, it's due to overall wear in the pivots (if all stickiness has been removed and trying it without the cable installed)

It is ultimately the weak point of the 9 speed era.

The (non replaceable) spring in the parallelogram can end up not strong enough to overcome Friction and wear as it reduces in length towards top gear.

(The rapid rise models are cheap and provide quite a few spares, as well as being in better average condition because most riders don't like them)

Shimano techdocs might show you other derailleur parts that will do the job.

If you want to strengthen the b- spring:
Some springs can be persuaded to provide more tension with a little bending, occasionally heat, but I don't think this shape lends itself.

The spring could be shortened a little and a new hook formed on the end if you have a good heat source.

An alternative fix can be to put a 1mm washer between the derailleur fixing bolt and hanger. This increases the derailleur reach - assuming you have some spare for 1st gear.👍
 
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Hi bikeworkshop,
Thanks for the detailed and informative response!

Essentially it will make the shift to the big sprocket of my 9 speed cassette fine, but the distance between the sprocket and the derailleur pulley is minimal, even with the B-limit screw all the way in. That shouldn't be an issue with the parallelogram spring, right?
 
The top jockey position is determined by the derailleur design, with a little adjustment from the b screw.
Interestingly the chain length has an effect on top jockey position too, and going up or down a pair of links in length can sort things out.

Sometimes you can replace that b-screw with a slightly longer one.

Shimano tellyou largest sprocket size for their dérailleurs.
You can usually go 2 teeth larger, and then 2 more with the b screw bodge.
 
I might be wrong but didn't the M950/2/3 mechs have a little screw on the main parallelogram spring @bikeworkshop for increasing the tension marginally? Like it was an offset screw so you had normal and an increased position, rather than finely adjustable like a preload collar.
 
M900 had a main spring adjuster - I'll look at an m950 next time I'm in the shop - I dont think this will increase the pull into top gear position though, as the spring's about done there.
If it has one though it's worth a tweak👍
 
I had vague memories of adjusting it on some mechs, and I don't think it was later ones or SRAM, but it might have been. On normal mechs it would help drop it down the block wheres in this case it would help move it up, but I don't think that's the issue that's being encountered. Worth a shot if it is adjustable though, it certainly wouldn't do any harm.
 
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