UKC

I have a moderately decent full Susser approx two years old and the gears are getting a bit crumby, chain drops off, gear changes aren't as smooth as they use to be.

The main annoyance though is that the lowest down tiny cog inside the rear derailleur pops out of place frequently on rough terrain and the chain slips off it and grinds around the cage until I realise when I try to change gear and I have to get off and pop the cog back into place and put the chain back on, so I'm ending every ride covered in oil.

It's a shimano xt model and I'm wondering if people think it's possible to:

A) get it repaired at an LBS
B) replace just the rear derailleur leaving the chain and everything else the same. (I'd want to get a Saint model) - I've heard ppl say sometimes chains and gears are shaped to fit each other through wearing each other down so I'm worried this wouldnt work.
C) would I have to replace the whole chainset?

Thanks

Tl;dr: can I repair my rear derailleur or should I just get a new one fitted, or replace whole chainset?

In reply to elliot.baker:
A) yes
B) yes
C) no

They are repairable - mine ate the teeth off the last cog, and I replaced it with a £6 ceramic spare from eBay.
You can sort of unscrew one side and swing it all open. There will be videos on eBay.
Or a bike shop will sort it no hassle.
It is a bit fiddly as it's all under tension. I tried to swap mine for a spare which turned out to be broken, so it was a bit of a faff for me.

I'd say clean it well, inspect and compare to photos online, then decide. It might just be a missing screw.

Maybe consider a new chain while you're at it.

In reply to elliot.baker:

After 2 year use the cassette and chain (and maybe the chainrings) are likely to be quite well worn and you are likely going to need to replace both the chain and the cassette at the same time as the chain will have "stretched" as they say even if it's actually just worn and the cassette worn to match it. You can measure this in may ways with various gauges or just a good rule, each link should be 1/2 inch or about 12.7 mm so if you measure a dozen or so links and take the average and ideally you'd get a number showing less than 0.75% extension.
Also if you look at the cassette teeth in the smaller cogs if they are shark and look like shark fins then that's bad.

Regarding the rear mech, you can buy replacement jockey wheels that are simply changed and if the rest of the mech is in tidy condition that should sort you and save you a small fortune.

Hope that helps.

G

In reply to elliot.baker:

Sadly, after two years, I'd expect you really need to replace the chain, cassette and probably the rear mech too to get it all running sweet. It may just be chain stretch that is causing the pop off but I suspect the rear mech tension Spring is sagging a bit. The rings at the front are probably OK.

In reply to gethin_allen:

thanks for the tips folks.

Some of the teeth look exactly like shark fins on inspection, but some look completely fine... does just having a few shark fin looking teeth mean that the chain can slip on those teeth and will therefore make the whole experience shoddy? I imagine that would be the case.

I'll see what the bike shop say about it I think, see how much different things cost. Might price up new rear mech and casette and chain because I'm sure that would make a world of difference. I've been contemplating going to 1x10 or 1x 11 for a while now if it's affordable anyway.

In reply to elliot.baker:

I normally see it on the very smallest cog of the cassette and the first cog built into the spider of the cassette (the first few being loose if you take the thing off the freehub).
Moving to an 11speed system would likely involve a new rear wheel and going 1x anything would require a narrow wide chainring unless you just keep your front mech set with the limiter screws as a chain guide.
The rear mech is probably fine if you change the jockey wheels so just a cassette and a chain would probably be fine.

In reply to elliot.baker:

I have a shimano saint sitting on one of my spare bikes that never gets ridden. Probably around 4/5 years old but has maybe only been out 10 times.

Happy to sell it on to someone in need, including a compatible cassette and chain (again probably less than 10 trips out) for £50. Send me an email if interested and I will get some photos over.

In reply to elliot.baker:

Some teeth on modern cassettes are sort of shark fin shaped to begin with to help with gear changes so it may not be wear that you are looking at. However, two years is a long time to have the same chain if you are using the bike regularly. When I was doing a lot of miles I was changing my chain every three months. This had the benifit of extending the life of the cassette (or block in those days) almost indefinitely.

In reply to elliot.baker:
I don't really understand your problem with the rear mech. I'm assuming you are talking about the jockey wheel (one of the 2 little wheels hanging down in a cage from the rear mech). I can't see why it would 'pop out'. Not something that has happened to me in over 30 years of mountain biking. The jockey wheel screws into the cage so would need to be screwed back on not popped on so something seems wrong there. XT mechs are tough and would not need replacing after 2 years unless hit. Wear does not make them pop out, it makes the teeth spikey.

In reply to elliot.baker:

Leaving aside chain wear and cassettes, your bottom jockey wheel problem is probably down to the derailleur cage becoming loose or bent - Loose is more likely so that the gap between the jockey wheel and the cage is to great. Tightening that up should fix it, but given that you've been clunking along with the chain stuck between wheel and cage, the cage is probably a bit bent too. A quick tweak with an adjustable spanner should fix that. It may also be bent and running at an angle, which would also account for the chain hopping off (especially if you back pedal). More tweaking might fix that, or it might not. Of all the gear components, it's probably the least sensitive to poor alignment, so a bit a blacksmith-grade fettling should sort it.

In reply to blackmountainbiker:

I am talking about the jockey wheel closest to the ground (when the bike is sat on it's wheels).

And when I say "pop out" I mean it is sat very slightly off it's axis, as in both the centre of the wheel is not centred in the cage and the jockey wheel itself is at an angle, maybe only a couple of millimetres out. If you push it quite hard then it sort of "pops" back onto it's axis and straightens up and this makes the chain fall off less. If I don't pop it back into place then the chain falls off a lot.

I might see if the cage can be tightened up as nniff says... see if that works.

thanks

In reply to elliot.baker:

Okay. They should have some 'float'. Does the chain come off the jockey wheel?

In reply to blackmountainbiker:

Yes it does, then it grinds along inside the cage between the jockey teeth and the inside of the cage, quite horribly, until I notice, which can be a more than a few seconds if I'm involved in going down hill or something.
I generally notice when I back pedal and the chain doesn't go back through the derailler then I have to stop.