Have I busted the cassette?

[Manonabike]

I have a cassette which has done under 1500 miles. I also two chains which I swap, at least, every other week, so each chain has done about 700 miles. I did check one of the chains last week and it had expanded but very little, no need to change it yet.

I noticed the other day that the chain began slipping on one cog while doing hills.... the problem is getting worst and it's involving more cogs now, however, the chain and cassette combination work fine on the flat

Have I busted the cassette?

 

[HLaB]

It sounds like the chain wear doesn't match the cassette wear, quite why this has happened given what you describe I'm unsure . Or could it be slackness in the gear cables as they've stretched overtime . Is it possible the cassettes were installed slightly differently each time . Its normal however for the system to behave it self on the flat but gears slip when you are on a climb as in the latter you are putting more strain on the system and there can sometimes be a small deformation in the frame.

 

[PpPete]

If the rear mech cable tension is right and the gears index correctly on the flat, try taking the cassette off. Are all the splines on cassette & freehub OK?
Unlikely you'll have broken anything but worth a look.
Next candidate is the freehub.
Symptoms sound like a freewheel on it's way out: first one cog then more start slipping under load as the pawls don't re-engage. Usually happens in cold weather though, and with a freehub it's difficult to see how it would happen on one gear and not another.

 

[Manonabike]

I haven't had any issues with the gear index on the flat, having said that I have not checked the adjustment since the cassette and chains had done 250K.

I have a brand new identical spare cassette that I could try ultimately, however, I will swap the chain and do the routine maintenance before I try again.

The freehub is also same age as cassette and chains.

 

[Manonabike]

I think I cracked it!!!!

Yesterday I took the wheel off and on inspection I noticed the cassette has come a bit loose. Followed torque settings guidelines to tighten it up and I tested it this morning..... all seems well now.

Thanks for all suggestions