Hi guys,

Not sure about this one as there is probably more than one issue. About 6 months or so ago my old shimano (original on bike) snapped and basically was worn. So I replaced it with a SRAM PC951 chain and up until about a week ago had no problems. Made sure I kept it clean and lubricated. about two weeks ago the chain snapped and so I replaced a link with the spare ones I had left over when first fitted. The, last week the chain snapped again and so I replaced two extra links as the chain was a bit stiff. Checked that the chain links were fine and carried on.
I normally use the middle chainring and mostly as where I live is farily flat, so I have it on the lowest cog on the cassette. Every now and then when pedaling reasonably hard the chain seems to clip. If I move it up a cog the slipping stops.
So I checked the rear cassette and the chain seems to sit right on the teeth, however the middle cog they do not.

I'm thinking a few things now. Because I replaced two or three links for new ones on a reasonably worn chain this has caused a problem because most the links are stretched. Or, the middle chainring is worn and needs replacing, or the rear cassette needs replacing.
Failing that all three which is not the option I'd like to consider...

I'm just stumped why it is only slipping in the smallest cog??

It's slipping on the smallest sprocket because it has the least number of teeth engaged.
It is possible to wear out chainrings, but there's a rhythm to it. A cassette will usually outlast several chains, and a chainring will usually outlast several cassettes. The key is to replace the chain before it gets too bad.

Haven't tried adding a few fresh links to a chain in use, so I can't offer much help there. But I'd suspect stiff links first.

If you've ridden one chain to destruction, then it would probably have been a good idea to replace the cassette as well.

Looking at a cassette is a so-so method of checking for wear. With all the ramps and undercuts it's really hard to tell what is wear pattern and what is engineered.

Replace the chain and casette now. Problem will be solved.

Cheers for the reply. The chain was stiff but I loosened the links so don't think that's the problem. Also checked for wear on the cassette and chainring and they are showing signs of slight wear, but I think it may be the chain as it only happened when I put new links on there. Also read that you're supposed to change your chain every 1000 miles and I must be close to that.
Cheers for the reply

Was thinking of doing this. Just typical that things start to mount up costs wise and my wife will love me!!
Cheers

The other issue is you need to figure out what you're doing wrong to have a chain break repeatedly. I've never broken a chain in 26 years of riding.

Yeah good point. Thought maybe because I'm heavy footed and need to treat it a little bit better.

Do note that performance doesn't increase anywhere near as much as the price does when you go to (supposedly) nicer parts. I am quite happy running KMC chains and a HG-30 cassette on my commuter. At a grand total of 30 USD upkeep really isn't much to cry about.

Chains just don't break like that and there's no need to treat them easy. Something else is wrong.

Could your chains be breaking at the links where you joined them?

In any event a new chain and cassette will fix everything.

I used the SRAM snap link supplied and the breakage happened elsewhere. Chain seems fine now and I checked the teeth on both rear cassette and front CR. Cassette small cog does look worn so I might do as advised and get new cassetts and chain. Cheers guys

You are obviously more heavy footed than you realize and far more of a masher than the rest of us. But by using mostly the middle ring and smaller rear sprockets you are generating more tension in the chain than you would if you use the larger ring and bigger rear sprockets. This is purely a case of leverage. The smaller the front ring the more tension you'll get in the chain for a given pedaling pressure. If you switch to the big ring and use the bigger rear sprockets in the middle of the cassette you will generate less tension in the chain, less breakage and use sprockets front and rear that have more teeth and spread the load out more and wear less quickly.

But at this point I'd start by replacing the chain and cassete. It's seen enough injury and woe. If you can find one go for a 12 to whatever cassete since by using the big front ring more you won't need the 11 by the sounds of it. This will shift all the sizes down one position and allow you to ride with the middle or smaller rings on the cassete. That will reduce the cross chain angle a little which will help lengthen the chain life again.

It sounds as though you are sizing your new chain properly, but just in case, make sure about that.

First it sounds like your cassette is worn out.

Second, it sounds like you are joining the chain by pushing pins back in, instead of using the master link.
You don't manually push pins into a SRAM chain, unless you enjoy breaking chains.
If you need to lengthen it, you use additional master links.

Thanks for the posts guys. Makes sense about applying pressure on the smaller cog and I have ordered a new cassette and chain. Shimano HG 50 cassette and SRAM PC951 chain.