BikeNC

This happens when downshifting to the small ring, on my double. It only happens occasionally, with it happening three times today on my 60 mile ride, and once on my last 30 mile ride. The drivetrain, including derailleurs are Dura-Ace, with only 300 miles on them. The derailleurs have been adjusted according to Parktools specs, and shift very smoothly and precisely, with no chain rub or chatter whatsoever. I have the low screw, on the front derailleur, adjusted as close to the chain as possible without rubbing, in the lowest gear. One quarter of a turn more and it rubs. I don't cross chain, as a matter of fact I'm usually near the middle of the 10 speed cassette when I downshift to the small ring. FWIW, my chain is a KMC-DX10SC. Everything works so well, but to have this happen on occasion is aggravating, to say the least.

Has anyone else had this problem, regardless of derailleurs being properly adjusted? If so, what did you do to solve the problem? Could this be a solution? https://bikeparts.com/search_results.asp?ID=BPC318796 I hate to resort to this device, but if it works I may consider it.
Thanks in advance, for your help.

Mike

froze

Your front derailleur is probably out of adjustment; to save me the time of explaining it all see this site for details on how to adjust it: https://www.parktool.com/repair/readhowto.asp?id=75

You could also have a worn tooth or two and when you shift once in awhile it just so happens your chain hits where the teeth is worn then just slips off the chainring. You should be to see worn teeth with your eyes though.

I would try to readjust everything again per the website I gave.

BikeNC

Froze, with all due respect I explained in my original post that I had already adjusted the derailleurs (front and rear) according to Parktools specs. That includes the FD height and alignment, along with the high and low adjustments on both derailleurs and also the indexing. The chain shifts off regardless of being properly adjusted.

Mike

Ex Pres 

I would try pushing the tail of the derailleur out from the frame just slightly.

BikeNC

Thanks Bob. Sounds like it would make the downshift less "aggresive". Hmmmmmm....it just might work.

Mike

maddmaxx 

The N-Gear Jump stop is a very nice piece of work. Once on and adjusted, the chain will no longer fall off the small ring for any reason. This will let you keep the derailleur set up for agressive downshifting.

BikeNC

Thanks, Maddmaxx. I do like the way the bike shifts, and I'm positive everything is properly adjusted. I would hate to compromise the derailleur's performance just because of chain overshift that only happens once in a blue moon. With this in mind, I think I'll give the N-Gear a try.

Mike

Retro Grouch 

What about the high limit screw?

Sometimes if the derailleur is up against the high limit screw it puts the derailleur into a bind. When it does that sometimes the derailleur hangs up momentarily then shifts really hard over to the small ring. The fast shift causes the momentum of the chain to carry it over the small ring. The solution is about 1/8 turn of the high limit screw.

onbike 1939

Given that the op states that all adjustments are correct then this seems the most likely bet in my opinion.

Setting the gears up on a workstand is never exactly the same as when the chain is under tension when riding. I usaually have to make fine adjustments on the road to get it exactly right.

froze

Mike I read that, and understand that you properly adjusted it, but sometimes we miss something; so I gave you that site because it had other adjustments that maybe you didn't try or unknowingly messed it up, or didn't do it as properly as you thought. This wasn't intended to make you sound stupid, or you don't know what your doing, it was just for your aid just in case.

BikeNC

No worries mate I actually went completely through the step by step instructions, for FD and RD adjustments three times, thinking that I possibly missed something. The end result was the same on all three accounts. It's hair pullin' time

BikeNC

Sounds logical. Sometimes it's the little things that are overlooked, that cause the problems. I'll give it a try. Thanks RG

Mike

waldowales

Just install the Dog Tooth or Chain Watcher and get it over with.

Wordbiker

I disagree.

If the chain is shifting off the small ring, then the front derailleur is not adjusted correctly. IMO those devices are made to compensate for improper adjustment and shouldn't be completely relied upon. I've seen a few of them chewed through and cause problems with jamming the chain. I'm not saying they don't work, just that figuring out the derailleur issue is probably the better approach.

That said, front derailleurs do not always obey the adjustment instructions written for them, such as the outer cage needing to be exactly parallel with the rings. As Mr Barker stated, rotating the rear of the cage outward may improve the shifting. Also, the clearances given in most sets of instructions I've read can be played with. For instance, the "2mm clearance" of the cage from the outer ring can be made as small as barely clearing the ring. Just one millimeter one way or the other can make a big difference, especially with drivetrains that have non-stock gearing combinations.

There are a few other FD issues that don't typically get covered, such as cage distortion. Do you have another derailleur to compare and determine if yours is distorted? If it is, a squeeze or tweak can make a huge difference. One I have seen quite often with MTBs is the rear of the cage bent upwards. This happens when the chain gets coated with mud, chainsucks and the balled-up chain bends the cage. From above where the FD is usually adjusted from this may not be apparent, but if you look at it from the side, you will notice that the curve of the cage does not match the same radius point as the chainring. The chain will also rub the connecting bar or pin at the rear of the cage in smaller gear combos. Fixing it seems a bit brutal, and involves sticking a long tool through the cage and "cold-setting" it back until the radius matches again.

Sorry to post a novel, but in my experience the instructions are good for learning the theory, the tweaks come from experimenting with and sometimes pushing the boundaries to see what will happen. I honestly hope I didn't offend anyone, but my opinion is that if all parts are compatible and designed to work correctly, I'll kick my own ass until it's working properly or find out exactly why it's not working.

IK_biker

Not quite. They are a lifesaver for a bit unusual setups, where the FD has been adjusted to the MAX of its capability and all options have been exhausted.

I run 50-39-28 in the front, chainstay is on the shorter side, and no matter what I did, my chain used to drop onto the BB shell during rapid shift from large c/ring to granny, which is often necessary for the places I ride (western NC, lots of downs followed by severe ups).
I have been adjusting FDs since 1967 and there's not a single trick in the book I am not familiar with.

Chain-watchers do a great job, along with a properly adjusted FD. N-Gear is what I use, since the other varieties would not work on my bike (the weld between seat tube and BB shell leaves insufficient room for installing these, due to my smallish granny).

Wordbiker

Rare exception noted.

Perhaps it would've been more correct to state that they should not be a first line of defense instead of adjustment, especially not before trying all the tricks in the book...and perhaps a few that aren't.

BikeNC

Hey everyone! I decided to give the N-Gear Jump Stop a try. It's well made, easy to install, and best of all, it works! I've logged 200 miles since the installation, and haven't dropped a chain since! I agree that no device is a substitute for a well adjusted derailleur, but if your derailleur is properly adjusted, and everything you've tried has failed, then the N-Gear is the answer.

Talk about great customer service! Nick will send you the N-Gear to try before you buy. You only send payment if the N-Gear performs to you satisfaction. If you're not satisfied with it, simply send it back.

Here's the site: https://www.gvtc.com/~ngear/


Mike