Skipping chain blues

[thomas]

Lately a lot of TCC members including yours whiningly complained about skipping chains. During our last ride to Wada-toge both TOM and I suffered from that predicament: our chains started to skip during climbs. Philip seems to have experienced the same fate last Sunday.

In the cases of TOM and Philip the culprits appeared to be wasted sprockets or rear cassettes. I have a more persistent problem on my Panasonic bike at the moment which my LBS couldn't even solve after two lengthy sessions of applied cycle mechanics: the bloody chain wouldn't stop skipping.

What we did:

- checked the bottom bracket: just lubricated and in virgin condition

- changed the rear cassette to a new Dura Ace 12-25

- changed the chain

Results: still skipping.

What we did today:

- shortened the chain

Results: ditto. The guys are at their wit's end. They suggested that the 177,5mm cranks I currently use may apply too much torque onto the chain and the rear cassette. Anyhow, now it is up to the mechanical Gods in Shimano's High Temple to intervene. I am back to commuting on my German flatbar. uch:

 

[Phil]

The bad luck continues, eh, Thomas?

How about this list of possible causes:

http://www.webmountainbike.com/toptencausof.html

Sounds like you and your shop covered BB, cassette, & chain length...

Easiest thing to try next would be replacing the gear cables?

After that, checking for damaged freehub body, bent cage/hanger, loose hub, or wheel not centered in dropouts?

Me HATES mech problems... Hope you get it fixed soon.

 

[Philip]

Commiserations . . .

Thomas, I hope you get things resolved soon.

I am sure your mechanic will have checked it, but a bent rear derailleur would also cause the chain to skip. Its the only component you have not replaced.

Cheers,

Philip

 

[TOM]

Same chain skipping blues!

Lately a lot of TCC members including yours whiningly complained about skipping chains. During our last ride to Wada-toge both TOM and I suffered from that predicament: our chains started to skip during climbs. Philip seems to have experienced the same fate last Sunday.

In the cases of TOM and Philip the culprits appeared to be wasted sprockets or rear cassettes. I have a more persistent problem on my Panasonic bike at the moment which my LBS couldn't even solve after two lengthy sessions of applied cycle mechanics: the bloody chain wouldn't stop skipping.

What we did:

- checked the bottom bracket: just lubricated and in virgin condition

- changed the rear cassette to a new Dura Ace 12-25

- changed the chain

Results: still skipping.

What we did today:

- shortened the chain

Results: ditto. The guys are at their wit's end. They suggested that the 177,5mm cranks I currently use may apply too much torque onto the chain and the rear cassette. Anyhow, now it is up to the mechanical Gods in Shimano's High Temple to intervene. I am back to commuting on my German flatbar. uch:

Thomas! Looks like it is awfullly difficult to get out of this unpleasant situation for both of us! Just when I thought I had found the real cause of the trouble, it happened again...at the worst time, right as I was about to accelerate during the Mt.Fuji Hillclimb last Sunday.

Excerpt from my blog: .... When the first hilly part came, I found out to my enormous disappointment that the chain was jumping again in the mid-section...the rattling noise of my chain failing to get a grip on my sprocket was accompanied with my swearing NOT AGAIN! ...SH*T! and other profanities in flemish !! In no time I was the focus of attention. For the remainder of the race, I had no choice but to avoid using my mid-range gears and that was really nagging me!

(part omitted)

As I was climbing Yamabushi-toge on Doshimichi, right after Yamanakako, I suddenly remembered seeing my mechanic at Friend Syokai tightening the tensioning barrel connected to the rear derailleur.... The chain was noisy again and while pedalling uphill, I adjusted the cable into a tighter stretch (by turning the barrel on the down tube clockwise)...and SURPRISE SURPRISE!!....the noise disappeared and the chain was moving freely and engaging the mid-range cogs again!!!

That's it! While the combination of a new chain and an old sprocket was to blame for the same mechanical trouble with my Shimano Cheapos, this time, with both chain & sprocket brand-new, it is the slack in the tension cable which was the real culprit! Why had it been slackening? Two possible reasons: (1) the handle turned inwards at 90 degrees when rinko-ing the bike (I am left-footed and carry the bag on my left side rubbing the side of the bag - and the barrel adjuster -once in a while) (2) my having put plenty of oil into the barrel adjuster so that when exerting full power on the pedals en danseuse, the cable gave in and lost its tension.

Could that be the same cause for you Thomas? I will do some more experimenting this weekend with the downtube tensioning barrel to convince myself 100%. Will keep you posted.

 

[Terry]

Results: ditto. The guys are at their wit's end. They suggested that the 177,5mm cranks I currently use may apply too much torque onto the chain and the rear cassette. Anyhow, now it is up to the mechanical Gods in Shimano's High Temple to intervene. I am back to commuting on my German flatbar. uch:

Here is compatibility charts of shimano 9-10 speeds
http://cycle.shimano-eu.com/publish...hnical_service/faq_s/compatibilty_charts.html

The 10 speeds compoments are thiner than 9 speeds, so 10 speeds chain won t work very well with 9 speeds sploket (cassette).

Which shimano compoments do you have on your bike??

We will find a solution to your probleme

 

[trad]

try the little screw on the derailler?

The type of torque Thomas puts out is completely beyond my means, but have you tried playing with the little screw on the derailler? Its the one that adjusts spring tension and contact angle of the rear derailler. I have no idea what the technical term is, but its the one that that gives people some difficulty aligning things when reattaching rear deraillers.

I had a similar problem on my mtb a while back in a 24 hr race. The Shimano crew and Keith Bontrager (and his posse) suggested that I increase the derailler spring tension and angle of the derailler by turning the "little screw clockwise" a few times. presto, probem disappeared.

 

[Pete]

Sorry to hear about your mechanical problems recently Thomas.

I had some mechanical problems, with a skipping chain, when we went to Kusatsu in April. I managed to do a temporary fix by slightly moving the gear adjuster cable.

But the problems got a lot worse after the tour. The skipping started to happen in all the gears and then the whole of the drivetrain started to jam up. There was also some mysterious rattling sound coming from the rear of the bike. The bike was virtually unrideable.

The problem was a worn out rear hub. After a new back wheel was fitted, all the skipping and jamming of the drivetrain finished.

It's just a small possibility, but perhaps the culprit of your problems is coming from the rear hub.

I hope you soon get it all sorted out. Especially, before the Fuji Hill Climb.

 

[AlanW]

They suggested that the 177,5mm cranks I currently use may apply too much torque onto the chain and the rear cassette. Anyhow, now it is up to the mechanical Gods in Shimano's High Temple to intervene. I am back to commuting on my German flatbar. uch:

This clearly is not the cause. 177.5 mm cranks will produce 1% more torque than 175 mm cranks. Simple ratio. I would wager that professional cyclists produce substantially more than 1% extra torque than you (or me!).

Which chain do you have? Dura Ace 10 speed is CN-7800. The older, 9 speed Dura Ace chain is CN-7701 and this will NOT work with 10 speed. Have you joined the chain with the correct length joining pin? Again, these are different between 9 and 10 speed. 10 speed pin has two grooves around the 'break-off' piece to identify it.

You might be able to flex the frame enough to cause ghost shifts and skipping but I doubt it. Check the bottom brakect has the correct number of spacers (if any) each side so that the chain line is correct.

Good Luck,
AW

 

[thomas]

First of all thanks a lot for your replies, there is a lot of valuable info on this thread!

http://www.webmountainbike.com/toptencausof.html

Sounds like you and your shop covered BB, cassette, & chain length... Easiest thing to try next would be replacing the gear cables? After that, checking for damaged freehub body, bent cage/hanger, loose hub, or wheel not centered in dropouts?

Thanks for the link, Phil! The cage hanger is fine and we have checked the wheel alignment. The gear cables might be next on the check-list.

I am sure your mechanic will have checked it, but a bent rear derailleur would also cause the chain to skip. Its the only component you have not replaced.

Much obliged, Philip! We have also checked the rear derailleur.

Thomas! Looks like it is awfullly difficult to get out of this unpleasant situation for both of us! Just when I thought I had found the real cause of the trouble, it happened again...at the worst time, right as I was about to accelerate during the Mt.Fuji Hillclimb last Sunday.

I will do some more experimenting this weekend with the downtube tensioning barrel to convince myself 100%. Will keep you posted.

I have read your blog today, sorry to learn about your ongoing troubles. But what an inspiration, TOM: I'll definitely play with the tensioning barrel. And please teach me a few handy curses in Flemish!

Which shimano compoments do you have on your bike?? We will find a solution to your probleme

Hi Terry, long time no see! Thanks for your commiserations. All my components are 10-speed D-A.

Have you tried playing with the little screw on the derailler? Its the one that adjusts spring tension and contact angle of the rear derailler. I have no idea what the technical term is, but its the one that that gives people some difficulty aligning things when reattaching rear deraillers.

Hi Todor, thanks for the hint! I'll take a closer look at the spring tension on my rear derailleur.

The problem was a worn out rear hub. After a new back wheel was fitted, all the skipping and jamming of the drivetrain finished.

Pete, thank you! Someone else has mentioned the possibility of a wasted rear hub. Added to the check-list!

This clearly is not the cause. 177.5 mm cranks will produce 1% more torque than 175 mm cranks. Simple ratio. I would wager that professional cyclists produce substantially more than 1% extra torque than you (or me!). You might be able to flex the frame enough to cause ghost shifts and skipping but I doubt it. Check the bottom brakect has the correct number of spacers (if any) each side so that the chain line is correct.

Hi Alan, good to know that the long cranks are not the culprit. I do use the CN-7800 chain and assume that the guys at my LBS know about the correct pins. They also mentioned the possibility of me flexing the frame too much, but the chain keeps on skipping, even if I try to pedal as softly and smoothly as possible.


Thanks again everyone! I'll keep you updated.

 

[Terry]

Definitely, it is not because you are using a 177.5 mm cranks.
How about the freehub on your wheel ? You should normally put a puck (spacer) between a 9 speed freehub and 10 speed cassette!

 

[thomas]

Got it!

Today we had our third session at the LBS. The Shimano helpdesk had suggested we change the pulleys, but that didn't help. After a lot of tinkering we nailed the culprit down: as Phil had wisely hinted in his post, it turned out to be the freehub body. It seems that the inner teeth and pawls were completely wasted. My wheel is going to be sent to Trek in Kobe for further investigation.

Thanks again for your assistance!

 

[Pucci]

Grind

Thomas you pedal too hard. In future we will restrict you to istsy-bitsy, teeny-weeny gears.