Is it the chain or the cassette?

[BikeDaddy]

Hi everyone! I'm hoping one of you experts have come across this issue I'm having.

I recently changed out all my parts from one road frame to another.
Everything seems to be perfect except... Now when I shift up or down on my rear derailleur I seem to "free-pedal" for about 1/8th of a turn before the chain finally grabs onto the cog in the cassette. (By free pedal, I mean that the crank arm will move from say the 1 o'clock position to the 3 o'clock position without having any load from the rear wheel. It then engages the rear cassette quite abruptly.) The front derailleur doesn't have that problem and shifts smoothly. Also, the limits are set perfectly for both low and high cogs for the rear cassette. The only things that changed were the frame's dimensions and the fact that I used a new chain, although I did match the chain length almost exactly. Do you have any ideas on what might be causing this issue? Should I be looking at the chain, cassette or something else entirely? Any clues would be a huge help.

[Alex Ramon]

From your description it sounds like the pawls may be slipping in your freehub body. I would take a look at that first. If it's an old freehub it may be gummed up inside. Here's a video that shows how to replace it: http://bikeride.com/freehub-body/

[BikeDaddy]

Hi Alex. Thanks for your reply.

You guessed it... It is an old freehub. The only problem is that it's the same one I took off the other frame and it was working ok at that time and I don't have a spare one laying around. Is there a way I can confirm that it is the freehub before I go out and buy a new one?

[Alex Ramon]

If you're chain isn't riding up on the cassette and slipping teeth, the only other thing it could be is the freehub.

I'd take the cassette off and then play with the freehub with your hands. If you can turn it forward and it slips then you'll know for sure. However, sometimes they will only slip under pressure, so you may have to take it to your local shop to confirm.

[BikeDaddy]

Thanks Alex... I'll give that a shot.

[cyclerUK]

There is the choice of freehub or cassette teeth worn?

If the freehub was O.K. before the new chain then it makes me suspect the cassette.?
You say it does it when you change gear which again would suggest the cassette.

Have you by any chance still got the old chain?
If you put that back on it would prove if it's the freehub.
If the problem is still there then you know it's the freehub.

The other thing you can easily try:-
When riding let the bike freewheel and you will hear the clicking.
Now start pedaling and the take up should be immediate. If there is any obvious delay then Alex,s suggestion of the pawls sticking would be favorite.

There is also the obscure chance that the derailleur cable is sticky and causing the meck' to move slowly. But whether that would cause the problem I don't know?

[BikeDaddy]

Alex... So I took the wheel off and discovered there was a little side to side play on the cassette. I was hoping that was it so I removed it, cleaned out all the parts, assembled everything back so it fit snug and it still has the same issue.

cyclerUK... Funny you mentioned using the old chain. While I was offline, I had the same idea and tried the old chain but it was still doing the same thing with the old chain.

So I put the bike on the stand again and tried to switch gears very slowly to see if I could tell what was going on. I noticed that the problem might be that for a short time, when I'm changing gears, the chain rides on the top of the teeth before slamming down into place on the cog. I think that's what may be giving me the impression that for a short portion of a revolution that the rear wheel is not engaged before abruptly engaging again.

I'm guessing this points to the cassette???

[Alex Ramon]

Usually if it's the cassette, the chain will skip forward a tooth, but if it's riding on the teeth it sounds like it may not be shifting properly. This could be a gummed up shift cable, or more likely a bent derailleur hanger. Since you've changed to a new frame I'm guessing the derailleur hanger on the new frame is slightly bent. If that's it sometimes you can straighten it by hand, but it's better to use an alignment tool like this one. It's pricey though so it would be cheaper for your local shop to check the alignment to be sure.

[BikeDaddy]

Hi Everyone...

I took my bike to my LBS and it turns out it was a little bit of a couple of things... It was the derailleur that was slightly bent and the hanger was bent as well. They straightened both out for me and the bike shifts much better now.

Thanks for all your suggestions! You guys are a great resource.

[Alex Ramon]

Just posted a video that may help others with bent derailleur hangers:
http://bikeride.com/derailleur-hanger-alignment/