Drivechain problem (not sure what)

[Zippy]

I have a problem in the drive chain somewhere I think.

· Indexing ok both ends of the block, no play in the rear wheel or bottom bracket.

· B tensioning screw is correct – jockey not riding on the chain.

· Jockey wheels seem to be keeping the tension ok before the block although they are quite worn (plastic).

· Chain and block replaced at the same time and the problem seemed to get worse soon after the change.

· No play in the bottom bracket or pedal cranks. Both spin ok when not loaded.
· No falls on this derailleur, nothing twisted that I know of.

It feels like something is crossed slightly in the drive chain, like the chain is riding off angle and then correcting itself. When it does it sounds like the chain is twisting slightly and puts a small vibration up through the frame. Sounds like the chain is about to switch gears under pressure, but it doesn’t and indexing is correctly adjusted.

Any ideas? I think – go to a good cycle mechanic!

 

[spandex]

Did you change the block for the same make and model?

 

[Zippy]

I don't think so, but they were both pretty standard £25.00 models. New block is compatible with everything else in the drive chain. Changeups/down all ok, chain doesnt ride up or hop, all ok.

It just feels like the chain is offline and correcting itself somehow, which puts a twang through the pedals. I worry about the drivechain suddenly stopping against whatever problem it is when I'm in the middle of traffic.

It feels like the block is being pulled out of angle as it gets worse towards the steeper gears (more torque and further away from the centre of the wheel I suppose, so greater leverage) so the chain is constantly correcting itself.

Chain has never run off line or skipped - just this annnoying rumble-twang thing. I'm used to cycling being smooth!

 

[peanut]

why don't you stick the bike upside down and run the chain in the gear it usually gives a problem and try to narrow down where the sound is coming from
Sounds like the chain is trying to climb onto the next sprocket in which case you just need to re-index the gears . Does trimming the front mech take the noise away ?or is it definitely from the block

The other possibility is that the bearing has gone in your rear hub. Try removing the wheel and see if there is any play in the freehub by grabbing the block and wiggling it. You'll need to use some considerable force to test properly. Any play however slight means new bearings required. Perhaps your cassette lock ring has loosened ?

 

[accountantpete]

Did you check that the chain link was moving freely when you replaced it?

 

[Zippy]

why don't you stick the bike upside down and run the chain in the gear it usually gives a problem

Did this last night. The chain is not trying to climb or drop and the indexing is ok. When turning the drivechain by hand with no resistance there is no problem, only when working against a strain by placing my palm on the tyre when turning the pedals.

The problem seems to be coming from the block, though I can hear the clunk but not see how it is happening. Actually pedalling there is obviously more resistance so the problem happens more often.

There is a very slight amount of rotational play in the block related to the wheel, but I thought that was normal to compensate for any irregularities in the wheel, chaindrive balancing.

(Chain link is not stiff)

 

[swee'pea99]

Might there be anything helpful here...?

http://bicycletutor.com/adjust-rear-derailleur/

 

[peanut]

The problem seems to be coming from the block,

There is a very slight amount of rotational play in the block related to the wheel,

well theres the problem looks like.
There should be no play whatsoever. Thats what your jockey wheels are for .
if you can see wobble or misalignment of the block relative to the hub it needs investigating.
What type of hub /freehub do you have

 

[Zippy]

Sorry - closer inspection shows there is no play in the block, so no problem there.

I notice with the chain on my hardest gear, if I backpedal by hand the chain is trying to ride up to the next cog, though pedalling forwards it doesnt do this or catch on the next cog up. I don't know if that tells you anything.

I can't seem to make the chain ride off the smallest cog, no matter how far I turn the limiting screw. Gear cable is not tight at that setting, but not too loose either. That might be a clue?

 

[MartinC]

Sounds like the rear mech hanger could be misaligned. Check by eye to see if the mech cage seems to be in the same plane as the sprockets. You need a frame tool to check and adjust this so it could mean a trip to the LBS.

 

[peanut]

If your chain is trying to ride up the next cog then your cable adjustment is incorrect. There could be many reasons for this .

The same thing happened to my bike last week.I found it was due to friction drag on the gear cable under the bottom bracket. The cable has worn a tiny groove in the bottom bracket shell which was preventing smooth cable release.

I would check all the entire cable run from your lever to the rear mech. Make sure there are no sharp or tight bends anywhere.

Check the ends of all your cables to make sure when you cut them for length you didn't leave any ends slightly blocked by the end of the clipped outer cable wire. (very common)

Grease your inner cable where it runs inside your outer sections.
Grease the bottom bracket cable guide grooves.

Check you are fixing your cable into the rear mech correctly. Shimano have a guide on this. Don't do the natural thing of putting the bent over tab over the cable it should go to the side of the fixing clamp groove

Then go through the entire setup proceedure again.

Check first that your rear mech setting screws position your top jockey wheel centred directly over the smallest and the biggest sprocket teeth at each end of travel.

Set the B screw so that the top jockey wheel is the correct height above the biggest and smallest sprockets

Then set the cable tension in accordance with Shimanos guide
http://techdocs.shimano.com/techdocs/index.jsp

 

[mickle]

Sounds to me like a new chain running on an old chain ring or perhaps a chain which is too wide for the cassette sprockets, ie running a neight speed chain on an ine speed cassette. Or something.

 

[Zippy]

If your chain is trying to ride up the next cog then your cable adjustment is incorrect.

thanks peanut - the chain only wants to ride up to the next cog when hand pedalling backwards through the mech - could mean the jockey wheel is not in line with the cog.

I will check against the rest of your post and see if that sorts the problem. Many thanks.

 

[mickle]

You could maybe try not pedaling backwards. Just an idea.

 

[Zippy]

Dropped into cycle shop on way home. They measured the chain and found it to be well stretched beyond its useful life, though the block was ok. Both changed at the same time.

New chain bought - may sort the problem.