What is the maximum tooth sprocket you could fit on the back using a Deore DX rear derailleur?

[bold stelvis]

anyway - I was originally trying to suggest some ideas to help with the shifting - I'll get back to that!

if its always shifting ok at one end of the cassette but not the other, (and if you change the tension you're just moving the sweet spot rather than fixing it across the whole cassette) then that suggests that the cable pull at the derailleur is not quite enough so its 'shifting short' as it were

this is why you have to match shifters and cassettes - its not so much the 'speeds' that are important but that the shifter pulls the right amount of cable for each click to move the derailleur the right distance between cogs: that distance changes dependant on number of cassette sprockets (past 8 speed, shimano just started making the spacing tighter so more sprockets would fit on the same length freehub body)

If something is affecting that crucial cable pull for each click on the shifter then generally it will work for a few sprockets ok (there is always some wiggle room - about a 1mm or so) but gradually as you go further it becomes too much and you'll find a point where it won't shift

so thats likely what your trying to 'solve' on the shifting I suspect. Outside of simply mismatched components, here's a list of things that might be a cause:

old corroded cables
bad cable routing (esp any really tight bends)
slop in the cable routing (eg end caps not seated properly in cable stops etc)
incorrect cable attachment at derailleur (this is more likely than you might think - double check ithe cable is attached as shimano indicates and this varies quite a bit over different models. Deliberately clamping the cable the wrong way is a known method of tweaking cable pull to get normally mismatched components to work together)
simply overly worn components (unlikely I suspect)
derailleur hanger out of true
excessive play in the Freehub body or axle cones (the actual sprockets could be shifting around a bit)
old cacked up grease in shifters (liberally douse with WD40 if they feel sticky)

 

[FluffyChicken]

if you are ok with potentially having to undo stuff or further fettle to make it work then fine - tinker away! For sure its a a good way to learn

I think the sense of 'discouragement' is because at times you've been given overly specific information about 'what to do' which you seem to have latched on to, and with all due respect, without really giving the impression you've really understood the context well enough or know about about how all this stuff works generally with all the different standards and what works with what to be able to successfully wrangle what you think you want.

You do you of course, but I think myself and many others are a little sceptical about your aims. My first MTB in the late 80s had a bog standard MTB triple up front, with a 22 granny ring, a 7 speed cassette with a max 28T cog, and it could climb literally ANYTHING. Of course I was a teenager at the time and if stuff got hard (and it did) you just had to peddle harder

...

Probably a 26T ring?
28T was also common in the late 80s, the 24T became more common in the early 90s.
22T wouldn't fit the crank, unless it was something cool??

20T (and hence 22T) didn't come about until 1992 models and the smaller BCD of MicroDrive, but that then allowed them to drop from a 28T rear to a 24T rear and keep the same ratio. (Until 8speed came and you got the 28T back.) It was all for weight reduction and a closer ratio rear block, which makes cycling easier in general.

 

[bold stelvis]

Probably a 26T ring?

you're probably right - it was a LONG time ago

gonna have to look it up now - was a muddy fox explorer which had suntours top of the line 6000XCD group on it (not that this stopped my mates from relentlessly taking the piss cos it wasn't shimano...)

 

[retrobiker273891]

loaded up, touring style I can get it

I think there is a sort of law of diminishing returns at the low end though. In the MTB golden age 22 x 28 was 'enough' for pretty much anything if you had the legs - and even then that felt pretty spinny to the point you were on the verge of being unable to maintain enough forward momentum due to lack of speed. Does going ultra low to around 1:2 sort of ratio's really buy you much extra functionality, given you'd already be going very slowly? (I guess the OP would say "YES"!)

I can imagine its easier to peddle, but also even harder to keep up any sort of momentum that keeps you rolling. Anyway, each to their own!

That quote of having a big load and pulling off took on a whole new meaning.

 

[retrobiker273891]

anyway - I was originally trying to suggest some ideas to help with the shifting - I'll get back to that!

if its always shifting ok at one end of the cassette but not the other, (and if you change the tension you're just moving the sweet spot rather than fixing it across the whole cassette) then that suggests that the cable pull at the derailleur is not quite enough so its 'shifting short' as it were

this is why you have to match shifters and cassettes - its not so much the 'speeds' that are important but that the shifter pulls the right amount of cable for each click to move the derailleur the right distance between cogs: that distance changes dependant on number of cassette sprockets (past 8 speed, shimano just started making the spacing tighter so more sprockets would fit on the same length freehub body)

If something is affecting that crucial cable pull for each click on the shifter then generally it will work for a few sprockets ok (there is always some wiggle room - about a 1mm or so) but gradually as you go further it becomes too much and you'll find a point where it won't shift

so thats likely what your trying to 'solve' on the shifting I suspect. Outside of simply mismatched components, here's a list of things that might be a cause:

old corroded cables
bad cable routing (esp any really tight bends)
slop in the cable routing (eg end caps not seated properly in cable stops etc)
incorrect cable attachment at derailleur (this is more likely than you might think - double check ithe cable is attached as shimano indicates and this varies quite a bit over different models. Deliberately clamping the cable the wrong way is a known method of tweaking cable pull to get normally mismatched components to work together)
simply overly worn components (unlikely I suspect)
derailleur hanger out of true
excessive play in the Freehub body or axle cones (the actual sprockets could be shifting around a bit)
old cacked up grease in shifters (liberally douse with WD40 if they feel sticky)

Thanks for the suggestions.

I have bought a new cable for the RD which is probably the cheapest thing to try first so we shall see if that has any effect.

I am not sure about mismatched components as still getting to know the parts of the bike but isn't it true that generally shimano 9 speeds will work with shimano 9 speeds? The shifters are surely 9 speed, having checked the clicks. I gave the model number of the derailleur earlier, which is also 9 speed. Chain is also confirmed 9 speed.

Just a gradual process of elimination I guess.

I did have another go yesterday and it is definitely like mentioned, accurate to one side of the cassette only then off for the rest. I gave it one last try before buying the new cable but it was the same again even trying as best I could to make fine grained alterations to the barrel adjuster.