Ontarget

Greetings:

I'm a long-time lurker but a first time poster. Here's my situation: My 2013 Fuji Roubaix 1.3 (primarily Shimano 105) occasionally drops the chain when shifting from the large to small chainring under moderate to light pedaling. It won't do it in the workstand ... only when riding. I've adjusted the limit screw such that when in the small chainring/large cog combination the inside of the derailleur cage just barely clears the chain. An eighth of a turn more and the chain rubs.

In order to prevent the chain from dropping at all, I have to tighten the limit screw such that there's chain rub in the small chainring/large and second-to-largest cog combinations. The derailleur cage is parallel to the chainrings and the clearance height is about 2mm above the large chainring.

The chain line on this bike isn't quite to my liking, meaning that the chainrings are more out-board than I'd like. When in the small chainring/large cog combination, the chain is at a pretty good angle. However, I can't come up with a way to change this.

In my situation, the only solution I've come up with is a chain catcher, such as Deda Dog or Jump Stop. Any other ideas, or is this the route i need to go?

Thank you in advance for your replies!

Jim

fietsbob

hard to say from here , Sight unseen ..

I put on a Chain Minder or those Deda Dog or Jump Stop on my several triples, I even used 1 on my Single ring Crank on my Bike Friday.
It has a disc chainguard.

Chain line .. Doubles set in the center line middle of the cluster in the back .. its a split between the 2 . triples its the middle chainring ..

thats proper chain line by design standards . IDK what you would like it to be.

cny-bikeman

It's always helpful when posting to give us a time frame and context. Assuming this has not been occurring since you first had the bike, when did it start being a problem, and was there any type of incident or maintenance just before it started? Also, how many miles on your chain, and how much chain wear do you have? Also the 1st step in checking front derailleur adjustment is to check height and alignment.

DiabloScott

I put a 9-speed chain on an 8-speed crank one time, and no amount of futzing with the derailleur stops or cable position would prevent throwing on downshifts. Replaced with 8-speed chain and problem solved.

Maybe this applies to you as well.

FBinNY 

FD alignment can make a tremendous difference in balancing chain drop vs. no-rub trim. In some cases the situation improves with a different chain, or a slight increase in chainring separation.

FD adjustment, is one of those things that separates mechanics into artists and paint by numbers guys. You can do a by the book setup and run into issues, and it'll require actual skill to diagnose exactly what's wrong and fix it.

BTW- one thing that does cause chain drop is when the outer chainring trim is a bit outboard and the mechanic compensates by tightening the high limit. This has the FD jammed against the outer stop with excess cable tension, and produces a overly harsh snapping downshift which throws the chain inboard with some momentum.

Try this, shift to high, and pull on the cable by hand. If the FD does not move out a bit more, that may be the issue. Back off the outer limit, and adjust trim to most inboard position that doesn't rub in high (smallest rear). Then adjust the limit to prevent over shifting to the outside, and no further. That should leave the FD trimmed correctly yet with a bit of room to move out if you tug the cable.

rpenmanparker 

Campag4life advises that the FD cage parallel to the chain rings may not be as proper as ALL OEM instructions suggest. He advises trying different toe in and out arrangements of the FD. I could see how a very slight toe in (rear of the FD pointing very slightly toward the center line of the bike instead of straight back might help your problem. Watch out for the opposite extreme, large ring/smallest cog, of course.

rpenmanparker 

BTW chain catchers have become quite acceptable in polite cycling society. If that would fix your problem without further aggravation, there is no reason to avoid it. You won't be ridiculed.

fietsbob

the K-edge ones are absolutely Posh Chain Catchers for Road, Cross, and MTB Bikes - K-EDGE
particularly with braze on and Band adapter + braze on FD's..

rpenmanparker 

+1. That's my choice. They are very nice and not terribly expensive.

RPK79

Similarly I had this issue when I first installed my 5700 groupset due to a backwards 5700 chain. It also caused sloppy rear shifts.

Ontarget

I wasn't very clear. I know what textbook chain line should be. The midpoint between my chainrings approximately lines up with the fourth smallest cog in the 10-speed cluster. Hence, the chainrings are outboard.

Indeed, I should have indicated that I've had this bike for about three months, and this problem has been the case the entire time I've had it. I bought it for a steal from a LBS. The mechanic at this LBS is a hack, and I wouldn't normally buy from these folks, but I couldn't pass it up at the price I paid. I have about 500 miles on this bike, so the chain should be just fine in terms of wear.

My FD is jammed against the high limit. This makes for a quick and responsive downshift, but I see where you're coming from. I'll adjust as you suggested and see if it helps.

FBinNY 

Yep, quick and responsive, yet you forget to factor inertia. BITD, before STI and Ergo, we used some touch, shifting gently if the chain was coming from the inside, and more aggressively if coming from the outside.

Modern shifters don't allow for that, and use an escapement with shift speed dependent on the spring. This can be not enough or too much depending on the chain angle.

When Shimano brought out Di2, they brought touch back. The FD talks to the RD and adjusts shift action depending on where the chain is coming from.

I suspect that your desire for crisp shifting is part of the problem and things will improve when you adjust to avoid (or moderate) it. With some fine tuning you should reduce the likelihood of overshifting to near zero.

However, mechanical index fronts have the potential to overshift, and even many of the pros use chain keepers of one sort or another.

get it as good as you can, and see if the shift response is still up to par for you. Then if not happy, don't be too proud to use some kind of chain keeper. IMO- Having both no dropped chains, yet shifting the way you want trumps being a purist.

Ontarget

I wasn't really trying to achieve crisp and responsive shifting. That was just an observation of the way it's set up. I'm sure I can live with more moderate shifting, but I'm sure I can't live with dropping my chain. I'll try to adjust as you have suggested and if I still have an occasional dropped chain I'll just install a chain keeper. I appreciate all your guidance!