masi61

Earlier this summer I had all kinds of chain slippage issues with a new Taya 9 speed chain that I installed on my 3x9 Dura Ace/Ultegra (7703 shifters, 6603 crank, 9 speed SRAM or Ultegra 6500 cassette) drivetrain.

At at first I blamed the chain thinking the Taya chain didn’t mesh correctly with my (new) Sram cassette. Well today I installed a new Campagnolo C-9 chain and it slipped in the same way.

When it happens, it is at the most tragic time - such as when I am trying to climb in the saddle on steep climbs and being passed by cars out in traffic.

Not a good time for a malfunction!

I concluded at the time that the chain must must have slipped off of cassette cogs. The occurrence happens so quickly and when I am concentrating on climbing that - I really have no proof of where it is occurring. What a I mean is - is the slippage at the cassette or at the chainring? When I resume riding in the saddle, slowly I am able to make the chain behave if I keep the effort light.

So today, I went on a light 22 mile ride and only got out of the saddle x2 to negotiate a busy intersection and x2 for standing climbing (attempted) in the middle chainring of my Ultegra 6603 triple crank that has over 15,000 miles on it.

The last time the chain slipped, it was quite obvious that it came off the middle chainring and derailed down to the 30 tooth inner chainring. When back in my neighborhood I conducted a test - I did a standing climb while in my 30 tooth chainring and the chain didn’t slip this time.

I’m quite certain that it would have slipped if it were in the middle 39 tooth chainring. I know for a fact that this chainring probably is by far the most used of my 3 chainrings. I stared at the tooth profile of that 39 tooth chainring with the bike in the stand when I got home and some but not all of the teeth look like shark fins - kind of pointy.

Still I only have a working theory here, for all I know, a cassette mismatch may have oscillated the chain to make it come off in the front.

Am I on the right track to identifying, then eliminating this (dangerous) demoralizing chain slippage problem?
I can can provide a photo of the middle chainring teeth if that would help.

le mans

What gear are you in when attempting a hill climb? maybe inspect the teeth on the those spockets too
You might need a new cassette and chainrings to go with your new chain, they might be worn too

masi61

One additional question re: replacing he 3 tooth chainring on an Ultegra 6603 triple crank: will a regular 39 tooth, 130 mm BCD 6600 double chainring work or is there a specific middle ring that is just for the triple 6603?

Thanks!

masi61

The cassette is new. It happened with the Taya chain when is was brand new. Now the cassette has about 500 miles on it and the new Campy chain is doing the same thing the Taya chain did.

le mans

You can narrow it down to the chainrings then, a close up pic might help us help you

Newspaper_Nick

Very unlikely, but i suggest you to also check the freehub body. The symptom of a failing freehub body is exactly like a chain slippage.

PS: If the chain is new but the cassette is old, a little bit slippage on the most used cogs is expected. As you wear down the new chain, it will slip less and less.

masi61

I know the freehub body is not the culprit because in my 2-chain system, my SRAM PC-991 chain does not slip at all. If I were fit enough, I could climb out of the saddle in the middle chainring all day.

The cassette is NEW.

zacster

Chainring. I had the same thing where my chain slipped when standing, but it was a new chain and cassette. I took the bike to the park to test out the various combos and it would only slip in the big chainring, the one I used almost exclusively, and in any back cog. I could put it into a similar gear on the middle ring and it would be fine. I replaced the chainring and all is well. The teeth on the ring that I replaced were really worn down.

masi61

Interesting. I’m pretty sure that this is what is going on with me only in my case it is the 39 tooth middle ring that has gotten most of the wear.

Here is the current middle ring:

masi61

And Here is a brand new 6603 crank with new chainrings installed. I was hanging on to this but this is as good a time as any to put it to use. BTW, the lovely, virgin clear silver anodized finish is really something I want to baby so I have a plastic squeege and some “Crankskins” protective covers that I plan to install before riding this bike.

masi61

Hopefully someone can discern something from the used and new photos posted above. All the ramps and chainring scallops and enhancements or whatever you want to call them - I would think these could potentially wear faster than just a good old-fashioned 39 tooth/130mm BCD chainring for your typical Shimano double crank. I have used and like the old Salsa chainrings, I wonder how much worse it would shift if I went with one of those to replace the worn 39 tooth ring.

zacster

Your middle ring looks like my big one did. It is definitely worn.

79pmooney

+1 That middle chainring is toast. Whether a non-specific 110 BCD chain will work - hard to say. Shimano likes to have chainrings to work together perfectly for their great shifting and don't always stick exactly to the BCD standards. Try it, you have nothing to lose - unless you want to use that new crankset.

What I see here is just routine chianring wear. I'd never swap out an entire crankset because one ring was worn. And you might be introducing otheer issues - chainline, creaks. If the crankset works well, I don't change it.

Ben

Newspaper_Nick

Your middle chainring seems worn out, however, i doubt that it is the main reason of your slipping issue. Chainrings last a lot longer than the cassettes, they can take a lot of beating and still work. They are much larger than the rear cogs and the chain "always" wraps around it and stays in full engagement with at least a couple of the teeth on it. It is not like the rear cogs where partial engagement is necessary. It should be very unlikely for a chain to slip from the chainrings. I'd really like to see a video of such an issue. I did a little youtube search and could not find anything. Your problem really baffles me. I will keep track of this thread for the solution of this puzzle. Very interesting for a self-made mechanic like myself

PS: Here is what i think. Because your chainring is worn, maybe it puts the chain out of allignment in the rear cogs. So even if your chain and cassette is new, because your chainring pulls more/less chain than it normally should, your chain fails to engage in the cogs properly. So it slips from the cogs because of the worn out chainring in front. That is just a theory of course.

PS 2: Also check the chain tension. A slack chain will slip under all circumstances.

PS 3: Check the B tension screw of the rear derailleur. It should engage as much cog teeth as possible without making any hitting noise, especially on the biggest cog.

zacster

Not likely. In my case it slipped in the front, nothing more. Replacing a chainring is relatively inexpensive and easy to DIY.

masi61

Just an update to this thread: the chain slippage issue was most definitely due to the worn out middle chainring. I went back to using the gold ano Taya chain and it works fine now. I temporarily switched out the entire Ultegra 6603 crankset for a used Dura Ace 7803 and the chain slippage issue has stopped. I can now stand on the pedals while starting out at a traffic light in the middle chainring and I get no crunch and no slippage. Problem solved, yayy!!