Chain/ cassette problem

[Marin Maniac]

Broke a chain, got a new one. Adjusted the rear mech. Bike shifting as sweet as it has ever done.

Got one large probelm now though.

Chain seems to be rubbing on the rear mech hanger. It also looks like some of the rear sprokets (9 speed) teeth catch the side of the chain on part of the cranck revolution.

Old chain didn't do this.

Could this be the chain which is a SRAM PC951 or could it be the way the rear mech has been set up?

Help? I just want to ride the damn thing!

 

[HLaB]

When you replaced chain did you replace the cassette?

 

[spence]

Are you sure you've threaded the chain correctly through the cage?

As above, usually good practice to replace the cassette and chain together (rings as well). A new chain on a worn cassette or vise versa will give you problems. Try repairing the broken chain and re-fitting to see if the problems go away.

 

[Smokin Joe]

Odds on it's not threaded through properly. You've probably gone over the guide tabs on the jockey wheel cage instead of under.

 

[Marin Maniac]

Nope havent replaced the chain rings or the cassette and I'm pretty sure the chain is threaded correctly.

 

[HLaB]

If you've not replaced the cassette my guess is that it has worn to match the old chain and when you've put the new chain on, it doesn't quite match.

 

[peanut]

chances are when you broke your chain it wrenched the rear mech cage out of alignment.
Put it on the small chainring and one of the biggest sprockets and eye up the jockey wheels and rear hanger. Both the jockey wheels and the sprocket should be verticaly in line with the front chainrings.
Also make sure that the face plate of the front mech cage is still in line with the big chainring and about 3mm clearance when above the chainring teeth

 

[jpembroke]

Do you mean the hanger (i.e. the bit of the frame the mech attaches to) or the swing arm on the mech itself?

 

[Marin Maniac]

Not sure if you are right peanut as this symptom didn't occur immediately. It has only just started to occur yesterday after getting the chain length correct adjusting the rear mech.

When you turn the cranks while the chain is on the smallest sprocket and biggest ring as it is more noticeable whilst on the biggest ring, the chain rubs against the inside of the rear mech hanger.

I've also noticed whilst the chain is on other sprockets when turning the cranks anti clockwise, its almost like the chain wants to jump of that sproket onto the next biggest one, although it doesn't make the chain rubbing noise that you get when the indexing is out.

 

[jpembroke]

Just sounds like you need to adjust the high limiter screw to me. That'll move the mech inwards, away from the hanger. Once that's done, you can adjust the gears using the barrel adjuster. Also check the chain length: when on the biggest chainring and the largest sprocket the mech arm should be at a 45 degree angle (angle between ground and line drawn through centre of jockey wheels).

 

[Marin Maniac]

Well cleaned the bike today and had another poke around.

The tolerance between the chain and the inside of the rear mech hanger (where it attachs to the bike) is so small, however under load I don't actually think it rubs.

What the chain does seem to do is when its on the smallest sprocket, when you turn the cranks anti-clockwise, the chain seems to rub on the next largest sprocket and jumps ever so slightly. This symptom occurs on the sprocket in the middle of the cassette. When the chain is in the middle of the cassette when the cranks are turned clockwise, it causes a slight knocking noise.

I think all these symptoms are due to how the chain sits on the various sprockets. Could this be due to wear on the cassette by the old chain? I'm a bit loathe to believe that this would be the case as the bike hasn't done that many miles.

I don't think these sypmtoms are due to the indexing being out of kilter as the bike seems to shift really well.

 

[peanut]

The tolerance between the chain and the inside of the rear mech hanger (where it attachs to the bike) is so small, however under load I don't actually think it rubs.

What the chain does seem to do is when its on the smallest sprocket, when you turn the cranks anti-clockwise, the chain seems to rub on the next largest sprocket and jumps ever so slightly.
.

sounds like you have two things going on here maybe.
If your chain is trying to climb onto another sprocket it is sdefinitely a matter of adjusting your gears properly. Have a look on you tube or the Shimano site for instructions how to do that.It may well still shift the gears but from your description the indexing is out of sync.
Re the rear cage rub well you need to take the bike to someone that knows what they are doing . Its too difficult to diagnose on here with dribs and drabs of information.

 

[spence]

Just a quick thought. Is the wheel seated correctly in the droputs? If it's slightly on the sckew the all the alignments will be out.

 

[Marin Maniac]

Just a quick thought. Is the wheel seated correctly in the droputs? If it's slightly on the sckew the all the alignments will be out.

Yep!

Going down to the LBS tomorrow to see what the crack is.

 

[jpembroke]

It's not a Planet X Kaffenback is it? They had a batch of frames that wouldn't accept 11t sprockets because it caused the chain to rub against the chainstay. Oh the hilarity.