drive train help needed

[Ajax Bay]

Reinforcing what several others have suggested - the symptoms the OP describes are typical of a build up of friction in the cable: unsurprising after 1200 miles with limited tlc. The RD has had no hard knocks and the chain is well within wear limits.
1) Remove rear gear cable.
2) Give the rear derailleur (RD) a clean.
3) Replace with new cable, greasing the bits of cable which are going to be inside the outer. Ensure guide under bottom bracket is cleaned and greased.
4) Optional but for more assurance: replace outer lengths at the same time. Your LBS will cut the bits the right length for you if you take then old bits in.
5) Reset indexing (many good u-tube videos available).
6) Unrelated but bonus action (good for chain and general chain/sprocket operation): take the cage apart and give the jockey wheels a good clean and juice (possibly for the first time).

Ride with perfect indexing.

 

[screenman]

Ajax, why would you not check rear mech alignment after all it could easily have always been out.

 

[Citius]

Unless he's crashed it, rear mechs tend not to go out of line on their own. Unless you mean the limit screws?

 

[screenman]

Unless he's crashed it, rear mechs tend not to go out of line on their own. Unless you mean the limit screws?

I would disagree with you there and of course I do not mean the limit screws. I am yet to check a bike that does not require tweaking and I have lost count of how many I have checked.

 

[Citius]

I would disagree with you there and of course I do not mean the limit screws. I am yet to check a bike that does not require tweaking and I have lost count of how many I have checked.

So what would cause the mech to go out of line all by itself?

 

[Racing roadkill]

Completely against the general concensus I'm afraid. Generally, 3 chains can be fitted to one cassette, IF the chains were replaced at a sensible point. Ive been doing it for years.
In reality though, you COULD end up with a situation where your cassette would need changing...ie if you allowed the chain to wear to an extent where it destroys the cassette...but that should be considered the exception... not the rule.

Well I ride lots of miles, and often change cassettes and chains, my experience ( over 25 years and God only knows how many gazillion miles, and countless drivetrain rebuilds / replacements ) puts the 'general consensus' firmly in its place. That is that in my ( fairly extensive ) experience, you have to be very lucky, or have a fairly unused cassette ( for example, if a new chain snaps / fails after only a few miles ) in order for a new chain not to slip, on an old cassette. But hey what would I know.

 

[Citius]

But hey what would I know.

Not much, clearly. I can only assume you're on a wind-up, because someone who has been riding as long as you (supposedly) have been, really should be making more sense.

 

[Ajax Bay]

Ajax, why would you not check rear mech alignment after all it could easily have always been out.

I think that the actions I suggested would probably (ie 75+%) solve the OP's problem. I agree that, if it didn't, hanger alignment check would be the next step for these symptoms. But he has done 1200 miles and these symptoms have developed, so it seems unlikely that they've always been 'out'.

@Ihatehills - do have a quick look to check the hanger's vertical (when the bike is) (I'm sure you'd have noticed if it wasn't already given the effort you've already made to fettle this).

 

[Ajax Bay]

I think playing 'top trumps' with a pack of 'experience' cards is unlikely to get us far, either ones with a quantity or a quality metric.
@screenman likes checking the hanger alignment, invariably finding they need tweaking (assume you mean bending - I have always found too much hanger bending ends in tears) - I just suggest doing the most likely fix first.
@Racing roadkill prefers to change things well before they give any trouble (eg jockey wheels, chains, cassettes) and that is a perfectly reasonable approach - but is it the best advice? Several contributors seem not to think so. There's a balance between expenditure (on new parts) versus the reduction in risk of equipment failure. I suggest @Racing roadkill is towards the end of the spectrum (and happy there).

 

[screenman]

So what would cause the mech to go out of line all by itself?

Not a clue, but I know it does.

 

[screenman]

Ajax, I have not snapped one yet. When I was learning mechanics I was taught to make sure everything was straight before I started putting things together and adjusting them, stuck with me I suppose.

I do not think that you can check it by eye, which is why a skilled guy would use a tool.

 

[Ihatehills]

Once again thanks for all your replies, I didn't get a chance to have a look today as the weather was not inspiring and I don't really have any where suitably undercover to work
I think its likely That it is a cable problem so this I where I'm going to look first , although I have ordered a chain checker and will be ordering a chain when I can figure out what I need.
@Ajax Bay and @screenman, when you say check hanger is vertical, do you mean just a visual check? The jockey wheels don't appear to be exactly in line with the cassette and I assume they should be does this mean the hanger needs straightening?
I googled hanger alignment and not much came up past wiggle and the like selling a tool for it.

 

[Citius]

Not a clue, but I know it does.

So you're talking about a hangar which spontaneously goes out of line?

 

[raleighnut]

So you're talking about a hangar which spontaneously goes out of line?

It doesn't take much to knock em out of true but there is an easy test as to whether they're in line.
If you can get the indexing spot on across the whole cassette then they're most likely straight, if you can't it is worth checking em.

 

[screenman]

So you're talking about a hangar which spontaneously goes out of line?

No, but after a couple of thousand miles I see they need tweaking to get bang on again. In fact even the turbo bike goes out of alignment over a period of time and that is never even moved. As I said though I do not have a clue why, maybe mysterious forces going on.