Chain Keeps coming OFF! on HARD Initial Pedaling.........need a fix
 

What's up guys, riders and enthusiasts!

I am having this dilemma I need to fix.
It's racking my brain upside down and sideways.

Here's the Diagnosis for those that have encountered or
had resolved this issue in the past.

* My setup is 50/34T with 11-34T cassettte.
* I have this setup with ALL 11 speed groupset.
Front der., Rear long cage der,, 11 speed chain, 11 speed Dura Ace 9000 Crankset 50/34T & 9000 levers.

* Recently had a crash, noticed a rear der. scrape, nothing serious.
* Looking from top to bottom the pulleys look slightly misaligned. (1st and 2nd largest cog)
* Shifts smoothly on ALL gears (however) noticed when reverse pedaling on ONLY
the 1st & 2nd LARGEST cog on the big ring it shifts back down to the 3rd cog. But shifts right back to
the 1st cog when pedaling forward.
BUT, when on the 3rd cog reverse pedaling is normal (no skipping)
* Did a hard pressing on the big ring 2nd largest cog & the chain came OFF
causing me to crash at a light intersection. Kinda a scary moment.

Can this be a bent skewer or rear wheel not being tight enough? I noticed it came loose on
the recent fall, BUT, did a super hard squeeze today and it happened again! But rear wheels seems
tight and secure.

I am narrowing this down to the rear derailleur needing to be replaced?
Any thoughts, confirmation to this? The pulleys does seem to wiggle from side to side.
Chain too short? Also, noticed this happening on my 2 other bikes.

ANY comments, rants or clues appreciated.

This may be a significant clue.:foo:

Inspect the chain, each link.

"Once upon a time", I had an instance where the chain fell off the front small ring while climbing in the biggest gear of the cassette. It didn't happen otherwise. I noticed there was a link in the chain that wasn't 100% pinned properly, and under heavy load (climbing) and with the chain at an angle (in the biggest gear of the cassette), the link would twist and self-derail off the inside of the small ring.

Given the greater chain angles these days it is getting more common to suffer with back pedaling chain drop from the rear's larger cogs to ones smaller. The chain is trying to seek a lesser angle. The simple solution is, of course, don't back pedal:)

As to the chain coming off when a hard effort is made I would need more data to really figure out the situation. First is where did the chain come off (a simple thing but rather important...) Did the chain drop off all the cogs/rings or just "shift" to another/adjacent sprocket? As mentioned a chain link twist of damage can cause chain drop.

Generally the only time a QR effects this stuff is when it can't maintain the wheel's position in the drop out. This should be simple to check for with a piece of tape indicating where the axle is secured at and thus any shifting from that location. Rear ders also generally don't cause chain drop unless they are twisted, damaged, have very worn pulleys or have really bad SIS adjustment (and also if the cable isn't freely moving along it's path).

More description please. Andy

Is the hanger straight?

Hi ridelikeaturtle. Thanks for the insight.
I will take that into thought and see if that
can be the case.

Many thanks for your thoughts on this Stewart.
I hear what your saying on the chain seeking a better angle.
I mentioned the chain drops off on the 1st and 2nd cog, but
assume you didn't read the whole post. rather long I know.

I bit the bullet and took off the rear derailleur and bent it back about 3-5mm
as it didn't look aligned when on the 2nd cog.
I wanted to bend it even more but didn't want to force a worse situation.
also, wanted to post a pic, but results wouldn't justify the angle.

Upon completing reassembly
it got a gear better. I can back pedal on the 2nd cog, but not the first.
I don't really care about back pedaling. just doing this to assess situation btw.

Skewers are not true also. Any recommendations on a strong model?

FINALLY, upon reassembling the R. DER. I noticed my cable housing was TOO long,
so this can be the culprit as you mentioned. need to test this out on the next ride
as I'm eliminating a few criteria's at a time.

STAY TUNED for updates.

Accident, scrape on rear derailleur. Hanger is bent. This is not something to eyeball straight. You need a Dag 2.2 tool or similar to align properly. If off, all sorts of shifting problems will occur. As far as the rear housing length, too short can be a problem, a bit long not a problem generally...

as others have stated a scrape to the derailleur is a good sign that the dropout needs realigning
there should be side to side play in the derailleur's upper pulley, it's a key part of indexed shifting

You should take the bike to a shop and see what is up before any more bending.

And did I read correctly that you took off a Dura Ace 9000 rear derailleur and bent the derailleur 3-5mm?

John

Did you bend back the derailleur or the hanger? Normally you bend the hanger if there's some bent, not the derailleur. Unless your derailleur actually got bent. Also there is a difference between a misalignment caused by bent hanger or simply the derailleur needing adjustment of the limit screws and cable tension. Before bending the derailleur you should first check the hanger alignment with a hanger tool, then set the limit screws and cable tension, and then if necessary bend the derailleur.

And when you say the chain falls off when on the largest 2 cogs, that doesn't explain how it falls off. Does it fall off at the front on the chainrings, or does it not fall but slips at the rear outward to a smaller cog?

Chain came off what??? Where exactly did the chain come off? Chainring? Cogs? In what direction did it come off? To the outside? To the inside?

This is completely beyond me: why would anyone go through the effort of beating around the bush for almost a full page, and then reduce the most important part (!) to just two-three virtually meaningless words "chain came off"? :twitchy:

I “think” the chain drops from the 10th and 11th cogs to the 9th. I “think” that is the “chain came off” meaning. It came off one cog to another.

John

You mean that by "chain came off" the OP refers to autoshifting in the rear? But why does the OP use the words "came off"? A rather weird choice of words. And how did the OP managed to "crash" then? I mean, I can imagine a combination of adverse circumstances in which sudden autoshift might result in a crash... but still...

Hi bldegle2 just reading this.
I understand your analogy, but most bike enthusiast do not
have this tool otherwise would do this first chance.

BUT, shifting up and down is perfect. no indexing needed.
I suffered yet another fall today. 3rd time in 2 weeks I think I need to bite
the bullet and get another rear derailleur to hopefully resolve this once and
for all! It's getting past annoying. thx


Ultegra R8000 (one with issue) 12-34T cassette 50/34T crankset
https://cimg6.ibsrv.net/gimg/bikefor...c303431ad8.jpg

Shimano 105 (comparison) 12-32T cassette 50/34T crankset
https://cimg9.ibsrv.net/gimg/bikefor...d1f33f596e.jpg

Hello tomtom yes you read it correctly.
Chain falls off to the rt. side of big ring.
It happened again today. somehow the tension pushes
it outward and then gets caught on the teeth causing abrupt
stopping resulting in me falling.

I'm a DIY so if I know I can fix this eventually I won't waste
money taking it to a shop when I can do it myself.

I've moved the pulleys sided to side and it is really not bad.
I've had worse cases in the past without this issue....hence
the dilemma. maybe it's because in the past it was a short cage
which wouldn't have as much play? not sure.

Maybe the chain is too short? which may explain this happening?
1st pic with Ultegra R8000 is one with issue.
Maybe there is not enough bend on the top pulley wheel?

2nd pic is one with the Shimano 105 has a little more bend.
but thinking chain is too short on this also? as I think the chain
skipped to the next cog on initial hard pedaling also. Added 3 links
on this because replaced 50T to 52T big ring recently. but haven't test
ridden it yet.

Yes, you are cutting your chains too short. That's why you are having the same problem on multiple bikes.:thumb:

I ran bike service departments in the 1970s and 1980s. There are plenty of jobs, e.g., wheelbuilding, I'm happy to DIY at home. Eyeballing derailleur hangers is not one of them. I was happy to pay a shop to align my bike's derailleur hanger after a teenage lout dashed out into the street (backwards and zig-zagging, playing tag) and ran into me.

Take it to a bike shop. Aligning the derailleur hanger is an easy job with the correct (expensive) tool and arguably impossible without it. They probably won't charge you much.

The "problem" of the chain coming off the largest sprocket while backpedaling is not a problem. It's physics. The gearset and chain are designed to derail quickly and efficiently. They'll do that pedaling forward when you shift (i.e., when the derailleur changes the angle at which the chain approaches the sprocket).

They'll also do it pedaling backwards in extreme gear combinations (i.e., with the chain approaching the sprocket at an extreme angle). Physics. (Some bikes have long chainstays or other characteristics that might diminish the likelihood of derailing resulting from backpedaling. I might even own one or two of those bikes, but I'll never know, since I don't backpedal.) (I also avoid shifting directly from first to reverse while my car is moving forward.)

Last, please don't use the largest two (preferably three) sprockets with the 50-tooth chainring. Yes, calling your bike a 22-speed is mathematically correct, but the drive train components will last longer if you treat them with respect, avoiding the big-big combinations (plural) and small-small combinations (again plural).

The chain does look shorter than I would use, maybe add 2 more links, but I don't think it's short enough to cause serious problems, there "appears" to still be a bend in the RD, so at least it doesn't seem completely straight and fully extended. But the angle of the camera can be misleading so I could be wrong.

What I don't understand is:
1) how does the chain fall off to the right side, "outside", of the chainring when you're on the innermost 2 largest cogs? Wouldn't the chain be pulled towards the inside, and not to the outside, since the chain should be angling inward from front to back?

2) And how does the chain falling off the chainring cause you to crash? When the chain is no longer on the chainring, it's usually hanging off somewhere on the crank arm. Continuing to pedal does nothing. The freehub will just idle and the hub wheel will continue to spin.

So I don't know why your chain would fall to the outside of the outer chainring when you're on the innermost cog.

Anyway, back pedaling on the largest innermost cogs can sometimes cause the chain to shift 1 cog over outwards, as someone else mentioned. It's just the chain angle. If your chainrings were moved closer inward, it may reduce the problem a little bit if it really bothers you, but depending on your geometry, it might just be normal. If you want to investigate, you should check what your chainline is at the chainrings. On a road bike with 130mm dropouts, if you have double chainrings, the midpoint between the teeth of the 2 chainrings should be around 43.5mm from the centerline of the bike frame. (inversely if your chainrings are too far inward, pedaling forward on the outermost cog may cause the chain to shift 1 cog inward. jump back and forth between or rub against 1 cog inward.)

And I don't know what you mean about the skewer for the rear wheel not being true. The skewer doesn't move at all and the straightness of the skewer doesn't have an effect on chain alignment. The skewer might not be manufactured exactly straight, but all it does it compress the frame dropouts against the locknuts of the hub. The downward load from the frame transfers to the axle of the hub, not to the skewer.

Also, a hanger alignment tool isn't that expensive. I bought a cheap Cyclus tool for around $25 but it wasn't very symmetric, so I bought an X-tools (bikehand) rebrand which was better for $45. You can buy one and check your hanger and bend it before you attempt to bend your RD. I found that my Shimano RD cage seems to be angled slightly outwards, and some other people replied to a thread that I posted that it's supposed to be that way.

You beat me to it.

I would check to make sure the BB or a chainstay, or the wheel itself is not wobbling/turning out of place. If the BB kicks out/in, I can see how that might cause the chain to walk off the sprocket.

Um... So you are saying that the chain comes off in the front. Why then are you trying to fix it in the back? Why are you talking about the RD then? If the chain falls off in the front, then most likely the problem is with the FD, isn't it?

Um... What "teeth" are you talking about? There are no "teeth" on the right side of the big ring. And how does it cause you to stop and fall? You are not talking about a fixie, judging by the pictures.

That chain is too short if it's the big-big combination.

Check to outside travel limit bolt on your front derailleur and adjust it so that the front deailleur can NOT push the chain off on the right side of the big chainring.

Cheers

Hi Guys! SORRRY for the long hiatus. PROBLEM SOLVED!!! with surprising results.

After yet another fall and a near fall I finally had 1 more option before buying another
rear derailleur. Swap back to the Ultegra 6800 50/34T cranks.

In the middle of doing so I noticed the chain position of the front derailleur
was a good 1 CM closer to the frame. A light bulb went in my head and also was
kicking myself why I didn't rememb I had to adjust this initially swapping the 2 cranksets.

CHECK PICS for assessment>>>>>

ULTEGRA 6800 50/34T

https://cimg9.ibsrv.net/gimg/bikefor...7ba020a843.jpg

Dura Ace 9000 50/34T

https://cimg3.ibsrv.net/gimg/bikefor...4b3a86ddd8.jpg

Dura Ace on the Left

https://cimg4.ibsrv.net/gimg/bikefor...e529454a43.jpg

Dura Ace 9000 (See front Der. plate top portion) leans toward front.

https://cimg2.ibsrv.net/gimg/bikefor...494a84aea6.jpg

Ultegra 6800 50/34t (notice chain upon swap positioned towards the rear front der. plate)
more to the middle than the right of the Dura Ace. ANGLING is tricky and may not represent
actual shift perception. But, is noticeable to the naked eye 1000%

https://cimg3.ibsrv.net/gimg/bikefor...bb73ee7550.jpg


The Dura Ace spindle is approx. 1/4" shorter than the Ultegra.
Haven't checked the Shimano website to see if this is correct or
I purchased a defective one as I got it used.

At any rate, even my LBS wouldn't have figured
this one out if he didn't have the 2 to compare. So luck prevails for me on this one.
What a trip. Was at the point of throwing my bike out the window in frustration hahahaha.

Thanks guys for all your inputs.
Check this one on your list for your future similar scenarios.

Don't pedal backwards when cross-chained. Applies to pretty much all derailleur bikes