Troubleshooting Chain Drop
 

I am experiencing chain drop under certain situation and hope to find out if something is not adjusted correctly with the FD or that I am doing it wrong.

The symptom: Chain get thrown outside of the big ring.

Situation: Always when I try to accelerate. I am usually in the small ring (50/34) and I want to up-shift so I will move the RD to either the 3rd or 4th cog. Then I am still spinning and want to move to the bing ring. At which time the chain is thrown outside of the big ring.

I measured the gap between the the FD and the big ring when they are aligned and it fits one penny so I think I am okay with the spacing. Could it be the FD limit adjustment?

If I do the same thing but shift the front with a smoother spin (not trying to accelerate then it shifts fine.)

Thanks in advance for any suggestions.

Yes, it's likely your high limit scew is not set correctly. Since you said the chain is dropping outside of the big ring, it sounds like you need to adjust the high limit screw to reduce the amount that it moves the chain outward. That's probably where your problem is.

definitely FD upper limit adjustment. Set it so that with the RD in the lowest cog (smallest) and the chain on the outer front chainring it just barely clears it. Don't forget to take the stress off before adjusting the limit screws. So see where you want it, then shift to the small ring so it isn't against the outer stop, then adjust it a little, shift to the big, check, repeat.

Just a general tip: don't turn limit screws or those weak inline barrel adjusters when they're under pressure.

Thanks for the tips!

Almost definitely the upper limit screw. Do like flatballer said.

However, I've had a couple cranks where setting the high limit so close that you could barely fit a hair between the FD's outer plate and the chain didn't prevent the chain from getting thrown. The cranks themselves would start to come apart (the spider was press-fitted onto the spindle and would work its way loose after a few hundred miles) and the ring assembly would wobble as if there was severe frame flex in the BB area (one bike was a CAAD8... flex?? Bah! ;)).

Shift into a tall gear on the big ring, stand up, and the chain gets tossed when my right foot went down. I let one bike get bad enough that I could do it at will.

Switched to another brand of crank and it never happened again.

What's on your bike?

Campy Chorus 10s, with carbon cranks, circa 2005.

I did a visual check now and the FD definitely clears the big ring by quite a bit. It might have been caused when I switched from standard to compact, and didn't readjust after moving the FD down.

Ah, ok -- yeah, you should be fine after repositioning the FD. Don't forget to detach/reattach the cable, too.

My problem cranks were Truvativ/SRAM. I even took a Rival-equipped Tarmac on a test ride and it had the same problem. 3 of 4 bikes I've ridden with either Truvativ or Rival cranks did the same friggin' thing, so I'm a shill for Shimano cranks now. ;)

Ask Andy Schleck, PM him, he has very good tips on how to fix this problems.

I am glad for this post as I am having the same problem.

the solution has been nicely explained by flatball so i won't say any more, but i have a question to OP.

How did this problem develope? I was told that once they have been set they should be ok but I set mine and this problem developed and I needed to readjust the FD. I don't know how it moved.

LOL, perhaps we should ask the OP if Alberto Contador was passing him at the time.

Post #6 - he switched to a compact crank and hadn't yet lowered the FD to match.

[QUOTE=tuxbailey;11164751]Campy Chorus 10s, with carbon cranks, circa 2005.

I did a visual check now and the FD definitely clears the big ring by quite a bit. It might have been caused when I switched from standard to compact, and didn't readjust after moving the FD down]

Bingo!

Well, I did lower it but I didn't adjust the FD side to side clearance :(

Nope, but I have been racing against the the virtual partner in my Edge 305 lately .... during my commute :)

maybe the wet b a c k version does hehehehe Norberto Contador :D

ps: I'm a minority so i can say those things

When setting your high limit screw don't forget to pull the cable to adjust it. You don't want to set the limits with your shifter.

Thanks.... But can you elaborate a bit on this....

Before fiddling around with your limit screws - how old ( or roughly treated) is your chain. Shift to smallest cog and big ring then pinch the chain on the big ring at 3 o'clock then pull straight out towards front wheel. If it starts to fall off the teeth at the top of the big ring ..... there's your trouble.

Two things that I think he's talking about --

You don't want to force the shifter to try to pull the cable farther than the limit screw will allow. Say that, for whatever reason, the shifter wants to pull to the last click, but the limit screw is only letting it go halfway -- that's a lot of extra stress on the shifter. You probably won't break anything unless you're an idiot and keep trying to force it. ;) Instead of using the shifter, then, pull on the exposed cable, like a drawing a bow & arrow, to move the FD.

At the other end, make sure the low limit screw is doing the work, not the cable. On my bike, I once figured out that the low limit was set so low that the cable was holding the FD in position instead. As the cable stretched (or the housing settled, or whatever people say), the FD would get a bit more out of position, and the indexing wouldn't work right. Now I always start FD adjustments with the cable detached.

gotcha. Thanks.

Chain is new, less than 300 miles. But I will also do this test just in case.

It sounds like you also didn't replace the FD with a compact version. They have a slightly smaller radius and match up to the big ring better than the standard derailleur. Might be worth it to pick one up on ebay to test.

Something like this?

That might be the last step if the adjustment doesn't work. I didn't realize that it makes a difference since the CT stuff was discontinued later.

I don't even know the size of the FD clamp for the seat tube...

Compact-specific FDs may not matter, even if you can find one. I didn't use one on my last bike, and don't have one on my current bike, either.