Derailleur problems

[Kookas]

I replaced inner and outer, but now it won't go into the highest gear. Adjusting the limits does literally nothing, and it has no issue with any other gears - it even goes into the lowest.

Edit: Nevermind, fixed it.

 

[User6179]

I'm finding shifting is really dodgy, even after being properly indexed by the guys at Decathlon.

My LBS says the rear mech is worn, and it does seem like it's worn a bit. But Decathlon said it wasn't.

It's hardly done 1800 miles in total, but my shifting habits are a bit sketchy and the like, as are my maintenance habits.

Do you think buying a new rear mech could fix my shifting problems? It's actually unsafe to ride ATM because I'd be accelerating and then it will snap to the wrong gear.

Of course, chain jumping and poor shifting could be a worn cassette/chain, but the derailleur has unusual side-to-side movement that does seem to indicate wear.

It's been 700 miles since I last replaced the middle ring, chain and cassette, too. I don't know who to believe.

If it is shifting down then it could be a sticky cable , so you shift down into a harder gear but the derailler stays where it is then you stand up and put some power down and it suddenly changes!?

 

[Kookas]

If it is shifting down then it could be a sticky cable , so you shift down into a harder gear but the derailler stays where it is then you stand up and put some power down and it suddenly changes!?

Basically, though I found that the most dangerous thing was that I'd try to shift down for a junction and it wouldn't have shifted by the time I'd reached the stop line, making for a choppy start when the lights went green.