stevelewis

I bought a near mint condition used bike but the chain slips when im in the big chainring (50t) and some of the cogs, usually 3 - 5 sprockets "down" from my easiest gear. Owner said the drivetrain (Dura ace 9000) has less than 2000 miles on it. I used a park tool cc3 chain checker device and the chain is not worn out. The cassette doesn't seem too worn out but I really can't say for sure. any ideas? The shifting itself is fine, the RD shifts without hesitation. The slippage does not occur when I shift, it tends to occur with sudden pedaling force. Or if I get out of the saddle and start to really go at it.

Help?

HillRider

I expect the shifting isn't lined up correctly and the rear derailleur isn't centered adequately under the gear you want.

Seizedpost

Maybe double check your chain measurement with a ruler just to be certain, though they should agree.
2000 miles is significant, in suboptimal conditions (dirty/wet/lack of mantenance) that's easily enough to cause substantial wear.
Dura Ace 9000 cassettes have all cogs larger than 16t made from titanium, and titanium cogs are known to wear faster. I wonder if it's possible that a titanium cog could have worn faster than a steel chain?

coupster

Your drivetrain has gears at the back, gears in the front and a chain that connects the 2 - all 3 wear out. Your seller probably replaced the chain to sell the bike. or He's selling it because it skipped on him and he thought a new chain would fix it. You probably need a new cassette. If that doesn't fix it, you'll have to replace the chain as well. Gears and chains pair as they wear and sometimes one will refuse to work with a replacement partner. This is an opportunity to fine tune your gearing setup for you and your terrain. So not only will your bike pedal smoother, you'll be more comfortable riding.

bkaapcke

Sounds like a worn cassette with a new chain on it to me. The particular cogs were probably the former owners favorites, so they are most worn ones. bk

DrIsotope

The chances of a few cogs being well worn on a DuraAce cassette at 2,000 miles is actually pretty good. At around 2,500 miles, the most used cogs on an Ultegra cassette I had were completely knackered-- and they weren't even titanium.

thumpism 

Don't overlook the possibility of a stiff link in the chain. Put the bike in one of the middle cogs on the back and, while holding the bike upright or having a helper do that, backpedal it and watch the rear derailleur. A stiff link will make itself known by causing a clatter as it passes through the S curves it takes back there. If you find one it can usually be fixed by working the link side-to-side at that point.

FBinNY 

There's probably some missing info here. Not blaming the OP, but he may not have all the facts himself.

For example, if the chain checks out, possibly we have a new chain on worn cassette issue, which is probably the most common reason chains skip under load.

Wilfred Laurier

Sounds like a new chain with a cassette that has seen several good seasons.

HillRider

In retrospect, yes it does. The OP said the bike was in "near mint condition" so I thought it was an adjustment issue. The factor of new chain on old cassette does seem reasonable now.

stevelewis

Thanks everyone for your input and advice. I checked for a stiff link and there was none. I did fine tune the rd barrel adjuster and increased the tension by about 1 full turn or so. I also cleaned the chain since it was very dirty. I'll go for s test ride tomorrow and report back. If the slipping persists then I guess I'm dealing with a worn cassette. That would be a huge bummer since DA cassettes are about $175!! Oh boy, might just go with ultegra to save money? Is there a cheaper Sram cassette that would be similar weight/performance to Dura Ace? Would it be compatible with my Shimano drivetrain?

Thanks

cny-bikeman

Does not match the symptoms. A stiff link would not be limited to only the large chainring, nor to only some cogs, and would only cause a problem every two crank rotations or more, not just with sudden pedaling force.

hefeweizen

Could the derailleur hanger be bent a little?

thumpism 

I stand by the need to eliminate the possibility. It's the easiest thing to check and in two minutes and you'd know either way, then move on.

Shimagnolo

Never waste money on a Dura Ace cassette.
Buy an Ultegra cassette;
It costs less, and will outlast the Dura Ace.
I love titanium for frames, stems, seatposts, etc, but titanium has no business being used on parts that wear.

Bike Gremlin

+1
The only difference I could measure between high and low end cassettes was weight. If it's a 10 speed, I'd go with the cheapest - Tiagra.

lightspree

You can use a Dremel tool to extend the life of the worn cogs, if you prefer that over replacing the cassette.

trailflow1

Have you tried this ? Which attachment did you use ? How much material do you need to take off ?

OP. Another possibility, there could be a problem with the pawls in your freehub which might be sticking and not engaging with the ratchet teeth properly, so its giving the illusion of a slipping chain as you put power through the cranks.

bwilli88 

Is it the right chain?
a 9 speed will skip sometimes with a 10 speed cluster

cny-bikeman

No, there's no need to eliminate it because it's not a possibility. I've heard people say the same thing about checking derailleur pulleys or hanger alignment. There's no percentage in approaching diagnosis in a random "it might be this" way. One is best served overall by developing a logical method of narrowing down causes to actual possibilities, based on presented symptoms.

stevelewis

How can I ensure that the chain is correct? Will it have a little "11" stamped on it somewhere?

stevelewis

Okay, the chain is HG701 which is the ultegra 11 speed chain. So that's not the problem.

Regarding the freehub possibility: when the slippage occurs, I hear a loud "gear crunch". Is that symptomatic of a free hub issue?

Wilfred Laurier

A terrible crunch sound/feeling is more likely to be a worn cassette, IME. A slipping freehub body is more of a 'bang' or 'bangbangbangbang' before engaging. Also, once engaged, if you don't let up on the pedals a freehub should not slip under additional force. It's hard to know for sure that you haven't let the freehub turn at all, though.

trailflow1

The crunch sound could be the chain clattering or misaligning on the chainring teeth or cassette teeth. When the pawls slip that is what generally happens as a consequence. The chain will behave very similar to a 'normal' chain slip. So diagnosing the problem by sound is not so easy.

Try removing the freehub and inspect to check the pawls move freely,and they are lubed and the springs are working correctly. And also look for any damage to the pawls or ratchet.

Seizedpost

You could also remove the wheel, put a chain whip on the cassette and whack it a few times to see if the pawls skip.