jambo69

I had posted this topic a few days ago and thought a new cassette had fixed the issue but broke the new chain today starting off at a light. Same issue as before as chain slips when I am cranking on pedal and skips over several teeth in rear cog. Does not move from side to side but over the top of the cog like it isn't properly engaging.

I have now replaced both the chain and the cassette...anyone other possibilities that I am not thinking of?? Not sure what else to try...

Paul

cpach

It is likely that your chainrings are also worn, and you are noticing this primarily in lower rear gears because they exert more torque on the chainrings.

FBinNY 

As noted, it might be slipping up front, but that's fairly rare on road bikes unless there's been a ton of miles.

I suspect an RD trim, and/or a hanger alignment problem.

Broken chains are also not all that common, so you also need to look at everything, going all the way back to the fundamentals, like how you spliced the chain, and how you shift under load.

One question I have is how old the bike was (in miles) before whatever caused you to replace the chain and cassette happened, and what exactly that was. If it was chain skipping, and you replaced the chain and cassette to resolve it, then obviously the fix didn't address the cause.

jambo69

Thanks for the help...here is a bit more information.

It is a mountain bike that is used for work commuting so maybe about 600 miles a year. Probably has been 3-4 years since chain was replaced so a bit of wear for sure. First sign of problem was old chain broke a couple of times and when I added another link (from an old chain), that new link was really stiff and never engaged with the rear cog and ran rough. No skipping at this point but I figured it was an old chain so replaced the entire thing. Then the skipping started where starting from stopped or a quick, hard pedal and it would skip over the entire back cog and nothing engaged with the cassette and I didn't move at all. This happened for a couple of frustrating days (I was hoping new chain maybe needed to loosen up or something...a slow pedal or start worked fine) and then replaced the cassette. Exact same problem with the new cassette when I rode in yesterday and broke the new chain trying to start from the first stop light. Replaced that quick link yesterday and took it for a quick spin and no change...a hard push on the pedals will result in chain skipping somewhere and no power to wheels.

I am not much of a mechanic...can you explain how a worn chain ring could affect or impact skipping at the back cassette? I can't quite visualize how the chain ring might cause this issue?

What is an RD trim adjustment?? Is that the high/low screws on my rear deraileur?

Thanks very much for the help...

leob1

First I would count the number of links on the old chain, if you still have it. Then make sure you have the same number of links on the new chain. I'd guess you didn't shorten the new chain when you put it on. Now the derailer doesn't keep enough tension on the chain.
If they are the same length, then you should adjust the "B" screw on the derailer. Just google 'how to adjust the b-screw'.
I've seen this dozens of times when somebody puts a new chain on a bike.

fietsbob

Index out of synch, so its trying to change gears. (?)