Bicycle Mechanics - Horrible Noisy Chain slippage under power.

hi all,

now I'm sure you've all seen one of these threads before, unfortunately I've looked though so many forums and found various Q&A's without seeing my solution, or specific problem. So if you can bare another chain slipping thread here goes.

I have a New Chain, Cassette, Back Wheel, Rear D�railleur, and hanger. Chain was measured against old chain, and again on the big cog to big cog with 2 link spare. All setup I've done myself, D�railleuring is seamless, and accurate. I can cycle around perfectly smoothly if I use the big front cog, and any rear cog, Although saying this I never go futher up then around the middle as I dont' want to twist the chain too much. I have to use the front biggy, as either of the other two cause the jumping problem, which occurs under force only, i.e. I can cycle around on flat surface and change gears up slowly with speed. if I start off in too high a gear then crunch, if I attempt to go up a hill then crunch. If I leave it on the front biggy, then its a very usable bike, apart from hills, and my legs are killing me!

Unfortunately I cannot recreate this problem on the bike stand, only when in proper use, and if I stare down at the drive train, it appears to be the rear cassette that is allowing the slip.

This weekend I moved the rear d�railleur so its arm was further forward, this means the chain is now running around the cassette in a very nice U shape. I had high hopes, but it didn't make the slightest difference.

Whilst it was on the stand, I did notice that the front chainset appears to wobble very slightly, this causes the chain to move ever so slightly from left to right as its running though, so I'm now wondering if I should replace this. The only thing that bothers me about this, is I can't imagine how this problem is being influenced by the pull of the top of the chain, I've always assumed its going to be from the d�railleur feed, rather then the cassette to chainset feed.

I've also checked the chain for tight links, and couldn't spot any.

any help will be appreciated.

I don't know what crunch is.
What parts are we dealing with here? Friction/Index shifting? 7,8,9,10s? brand(s)?

Is the chain riding up off the cogs and catching or is it ghost shifting up or down?

Check for a chain link that is tight or in a bind, maybe the one that you put together when installing the new chain.

Sorry, just read back and saw that you already checked for tight links .......

I don't know what crunch is.
What parts are we dealing with here? Friction/Index shifting? 7,8,9,10s? brand(s)?

Is the chain riding up off the cogs and catching or is it ghost shifting up or down?

To be honest I think its riding up onto the previous cog (toward the wheel).

I have index shifting on a 9 speed. I have the parts list somewhere will dig out and post.

I slacked off the rear cable completely to eliminate the indexing, and it still occurs.

I'm mostly perplexed why it doesn't do it on the biggest front cog, to me this points to a tighter chain, and also a pull to the right on the chain. I can take a couple of links out to try the tightness, but having seem some bike chains, I'm not convinced a slack chain causes this?

My mountain bike was doing something similar after replacing the chain and although it was a tight link that you don't seem to have, I would check the chain pins to make sure they're all pressed in properly. Mine was doing the same thing, I could only ride with the biggest ring up front or it would skip like crazy! Check the chain either by putting on the old one just temporarily and see if the problem exists before you start taking parts off that are more difficult to realign.

Your problem stems from the derailleur's inability to take up the chain slack. I've seen this time and again. What seems "right" on the stand doesn't really work properly from the smaller front chainring.

I would recommend removing one link and trying again. You'll be surprised. Phil G.

How does the chain line look? Is this a conversion you did? Why the derailleur hanger replacement? How is the alignment on the hanger/RD now (looking from the back and down)?

thanks for the suggestions, I don't have the old chain unfortunately, and to be honest I changed all these parts as my old chain/cassette had been used for over 2k miles without maintenance, this is why i've replaced most parts.

next chance i get I'm going to check all the links again, and I have been toying with the idea of link removal so maybe try this too.


cheers

front chain ring condition? worn?

front chain ring condition? worn?

well it doesn't look too worn. but am willing to believe it will have suffered from my lack of maintenance over the last 2 years. and as stated earlier, I think there is some slight 'wobble' coming from the chainset.

Purplemonkey, Years ago I started installing chains using the small-small method. It's just a bit more precise, IMHO. Works just fine with a triple, also.

Brad

My guess would be that the bike has been ridden primarily in the small and middle rings and though they don't appear to be worn, they are. This happened to a friend of mine last year during a race. He had done just as you have and replaced much of the drive train and kept the rings as they looked good. He even did some hard training rides for a few weeks prior to the 48 mile race. At about the mid point in the race, the rings wear hit that magic point where they looked good but would skip under pressure. He had to pedal lightly on all climbs and it was a frustrating day. He thought for sure it was skipping on the rear. It actually took both of us looking at it to see the skipping. Two new rings and the bike is now fine. Just my .02 YMMV

Your problem stems from the derailleur's inability to take up the chain slack. I've seen this time and again. What seems "right" on the stand doesn't really work properly from the smaller front chainring.

I would recommend removing one link and trying again. You'll be surprised. Phil G.


Chain length has nothing to do with driving the bike. It could hang completely loose in the little/little combo and still drive the bike just fine. If the length was set to the big/big plus 2 links it is as short as possible. If the chain doesn't hang loose or cause the lower Rd pulley to swing forward slightly and apply some tension, then it's too long, but it would still drive the bike.

It should be obvious whether the problem is at the chainrings or cogs. If it's at the back, then the indexing must be set properly so the chain is aligned with each cog. Note whether the noise is due to the chain skipping over the cog or whether it's trying to jump over to an adjacent cog. The later is due to improper RD adjustment.

Chain length has nothing to do with driving the bike. It could hang completely loose in the little/little combo and still drive the bike just fine. If the length was set to the big/big plus 2 links it is as short as possible. If the chain doesn't hang loose or cause the lower Rd pulley to swing forward slightly and apply some tension, then it's too long, but it would still drive the bike.

You say this with conviction which is encouraging, as I believe the same but not based on any personal experience. Your 2nd comment about the RD, I've already mentioned how it indexes smoothly and correctly up and down, and the skipping doesn't happen on the large front cog. I believe it is trying to jump to another cog, as I can't believe it would be slipping on the cassette. Whats your feeling about my test of slackening off the RD cable and letting it rest on the bottom stopper screw, which I assume would take improper RD adjustment out of the equation, as this test still shows the problem?

Purplemonkey, how about some pictures? Youv'e gotten a plethora of things to check. Anything else is going to require a close up view.
Let's see your RD alignment, you chain slack in the lowest and highest gear and you chain line from the rear. Also a good closeup of your chainrings (cogs in the rear, chainrings in the front).

ok, you asked for um.

got a few pictures here, two of them you can see are mulit images showing the chain length when set on different front and back cogs. I also changed the position of the rear derailure which is something I did on the weekend to try to get the chain to wrap better onto the casette but it made no differnece, and as you can see in one of the picture sets the chain goes really slack in this mode when on both small cogs.

I would add some more tension back into your "b" screw (3/4 to 1 1/2 turn) and my vote is for new front chain rings also, at least the low and middle ones. Blamp28 gets the 0.02c.

Also get a couple of more chains to swap out so that as they get dirty you can take one off, and put another on so you can clean the dirty one and still ride. Keeping chains cleaner will increase you cog and chainring life.

You say this with conviction which is encouraging, as I believe the same but not based on any personal experience. Your 2nd comment about the RD, I've already mentioned how it indexes smoothly and correctly up and down, and the skipping doesn't happen on the large front cog. I believe it is trying to jump to another cog, as I can't believe it would be slipping on the cassette. Whats your feeling about my test of slackening off the RD cable and letting it rest on the bottom stopper screw, which I assume would take improper RD adjustment out of the equation, as this test still shows the problem?

The RD should always rest on the small cog limit screw if adjusted properly. Adding tension should never pull the RD off that screw, when in the smallest cog. That screw can also be set improperly. If you loosen the cable, all that would do is make it so that is would not shift from the smallest cog to the 2nd cog without using more than one click and all of the indexing would be fouled up. If in doubt, loosen the cable and tighten it a little at a time until that first click shifts the chain up to the second cog. Then see how the rest of the shift to larger cogs works. Once all the shifts to larger cogs is working smo

I see worn teeth on the middle ring as well as the big ring. I can only assume the granny ring as well. The Chain will begin to skip in the big ring also before too long. If this were my bike, I would look for a deal on a new crank set as it will probably cost less than three chain rings priced individually. YMMV

I've had chainrings so worn, there were barely any teeth left, but no slipping.

I'm betting on sticky and slipping freehub pawls. Try another rear-wheel and see if you have the same problems.

There's considerable wear on at least the middle chainring and I suspect the small one as well. It's hard to predict just from the appearance whether a given worn chainring will cause skipping in practice since some that look very worn won't skip while others, with much less apparent wear, will skip.

I would replace at least the two smaller rings, or replace the whole crankset since that might not be any more expensive.

Here's some pictures of actual worn chainrings:

http://i42.photobucket.com/albums/e346/DannoXYZ/Cycling/ChainringWorn1.jpg
http://i42.photobucket.com/albums/e346/DannoXYZ/Cycling/ChainringWorn2.jpg

The thing is, worn chainrings do not slip. There's a difference in how driving versus driven sprockets engage the chain. If anything, worn chainrings grip too much and cause chain suck:
http://www.fagan.co.za/Bikes/Csuck

More info: http://yarchive.net/bike/sprocket_wear.html

Besides, the OP has narrowed it down to the rear-end anyway. It's really obvious when a chain slips on a chainring.

The OPs symptoms sound exactly the same as what I experienced on my bike when the chainring became too worn. In my case it was only the big ring with the problem since that's the one I used the most. The skipping first appeared only when trying to start quickly from a stop; i.e. when maximum force was being applied. Initially I also thought the problem was happening at the cassette, but eventually the skipping became more frequent and I realized that it was happening at the chainring. My large chainring was symmetrical so I could flip it over to get some more life out of it, but after another 30000 miles the teeth became too worn on the opposite face as well and the skipping started again so I had to replace the ring. (The chainrings in your pictures above look like they'd still work ok for some time if they were flipped over.)

Yes, frequently a worn ring will cause chainsuck before it starts to slip, but that wasn't the case with mine. Never had any chainsuck issues, but it did skip rather severely.

If all parts except the rings have been changed and there is a problem then I would assume the problem was with the rings.
Other possibility is freehub problems. I had a brand new road hub that creaked and slipped under power due to a flexy axle. You said you have a new wheel - what brand/model hub does it have?

hi all, thanks for all the advice so far. I took a step back today and counted the cogs on the rear cassette, at 9, then noticed the derailure has only 8 points, looked up my bikes specs and it was originally an 8 speed. So I reckon this might be the problem! sorry to be a complete idiot!

so I'm going to go get a new 8 speed cassette and see what occures!

these are the parts I bought and fitted.


1 of Shimano XT M770 9 Speed Cassette (1134T)
1 of Shimano HG53 9 Speed Chain


Actually got me thinking, would this cause the problem? is it not possible to upgrade to a 9 speed system?

What the heck does 8 points on a RD mean? The shifters for a 9 speed cassette would execute 8 clicks to reach the 9th cog.

i'll join the Greek chorus chanting for new front rings. Wear causing skipping can be visually subtle. It's also easy to blame the cassette - sounds and feels pretty much the same - but you have a new one.

I resisted replacing front rings too. But at 30k miles they were due for replacement.

hi all, thanks for all the advice so far. I took a step back today and counted the cogs on the rear cassette, at 9, then noticed the derailure has only 8 points, looked up my bikes specs and it was originally an 8 speed. So I reckon this might be the problem! sorry to be a complete idiot!

so I'm going to go get a new 8 speed cassette and see what occures!

these are the parts I bought and fitted.



1 of Shimano XT M770 9 Speed Cassette (1134T)
1 of Shimano HG53 9 Speed Chain



Actually got me thinking, would this cause the problem? is it not possible to upgrade to a 9 speed system?

If you have 8 speed shifters, and you fitted a 9 speed cassette and chain, all you need to do to change to a 9 speed system now is to change to 9 speed shifters compatible with your rear derailleur.

But, as mentioned by DaveSSS, make sure it is actually an 8 speed shifter. If you count 8 'clicks,' then it is a 9 speed.

What the heck does 8 points on a RD mean? The shifters for a 9 speed cassette would execute 8 clicks to reach the 9th cog.

sorry meant the shifter has 8 marks on it. anyway, it looks like i messed up, 8 speed shifter, 9 cog cassette and 9 speed chain.

I really hope chaning either the shifter or the cassette will now solve the problem.

cheers

Just wanted to say thanks to everyone who replied with advice. I have now changed the Chainset and this has fixed my problem. I'm still amazed that this was the problem, but there you go.

Happy ending. I wondered if perhaps the smaller chainrings might have had trauma damage (i.e. bent at some position) that wasn't visible in the photos. I've worked on many a mountain bike that had mangled rings that were no longeer parallel at all points, and they don't hold the chain well at all.

From my view of the photos, those rings looked like they had acceptable wear, even with brand-new chain on board.