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Discussion Starter · #1 ·
My Di2 shifters worked so well, UNTIL I changed the cassette from a DA 28T cassette to a SRAM XG-1190 RED 30T cassette. :cryin: BTW, the system has less than 1000 miles. I read where the SRAM cassette works even better than the Shimano, and I didn't want to go all the way to the Ultra 32T because of the derailleur arm length, so I thought this was good to go.. Is this BS? Well, I'm not sure if the new cassette is at fault or not.
What occurs is when I go to the 30t cog, after a few revs, it jumps back to the next cog. Now sometimes it stays in the 30t UNTIL I stand hard on the pedals, then it jumps back a cog. I'm guessing this is probably not good on the system.

Here is what I've tried so far:
1) Aligned the hanger
2) Adjusted the derailleur in 4th or 5th cog per Di2 instructions.
3) Adjusted the der tension to have more force. Helped, but not eliminated.
4) Checked the Hi/Lo limit screws.

So what do you think I go from here? I know...the LBS, right? Well, not opposed, but I am really interested in what's going on.
 

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Discussion Starter · #3 · (Edited)
Check that the wheel is installed properly and the quickrelease is tight.
Yes, locked and loaded!

However, I just noticed something when I checked. On the bike stand, shifting is smooth and easy into the 30t. BUT, within 30 secs, the derailleur jumps back one cog without any input. What's going on with that? :eek:
 

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I am new to the whole Di2 thing, only had it a few months. So this isn't Di2 specific but have you checked your chain length, going from a 28t to a 30t should be 1-2 more links.

SS-
 

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I've only seen a DI2 derailleur drop back a gear when the limit screw was too tight. Trying loosening the low limit screw a 1/4 turn at a time and check at each adjustment. If that solves your problem, then you're done. If not, then it's something that I've seen on a few Red22 cassettes and can't really offer any help as SRAM doesn't support that cassette on a Shimano setup.
What I've seen is the big cog (the Al one) is sometimes spaced a touch farther from the stack than it should be. It looks to be a manufacturing thing that has to do with how the Al cog is pressed and fixed onto the monoblock stack. A depth gauge would verify. If you found this to be the case, you could call SRAM but I'm not sure how they will handle it if you don't have a SRAM bike to test it on.
I've installed a couple of Red22 cassettes onto DA9000 bikes, and there is definately some inconsistency in the big cog spacing. But still, play with the limits first (more than you already have), the symptoms you describe point to that.
 

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'brifter' is f'ing stupid
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If the upper pulley isn't pinching the chain between itself and the cassette you're fine and just need to make sure the low limit screw is properly adjusted. If the chain can run smoothly on that large cog the derailleur should have no problem keeping it there unless it isn't adjusted properly.
 

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Discussion Starter · #11 ·
I've only seen a DI2 derailleur drop back a gear when the limit screw was too tight. Trying loosening the low limit screw a 1/4 turn at a time and check at each adjustment. If that solves your problem, then you're done. If not, then it's something that I've seen on a few Red22 cassettes and can't really offer any help as SRAM doesn't support that cassette on a Shimano setup.
What I've seen is the big cog (the Al one) is sometimes spaced a touch farther from the stack than it should be. It looks to be a manufacturing thing that has to do with how the Al cog is pressed and fixed onto the monoblock stack. A depth gauge would verify. If you found this to be the case, you could call SRAM but I'm not sure how they will handle it if you don't have a SRAM bike to test it on.
I've installed a couple of Red22 cassettes onto DA9000 bikes, and there is definately some inconsistency in the big cog spacing. But still, play with the limits first (more than you already have), the symptoms you describe point to that.
Superb information...that makes total sense, and something I would not have guessed. Being naive, I would have thought their Mfg was spot on. I'll get the calipers out.

If the upper pulley isn't pinching the chain between itself and the cassette you're fine and just need to make sure the low limit screw is properly adjusted. If the chain can run smoothly on that large cog the derailleur should have no problem keeping it there unless it isn't adjusted properly.
Thanks, here are photos of the engagement, which in my mind look okay:

Small/large:

Bicycle wheel rim Bicycle part Spoke Bicycle tire Bicycle drivetrain part

Large/large:

Bicycle tire Bicycle wheel rim Bicycle part Spoke Bicycle accessory

And no, I haven't figured out how to rotate the images. :mad:
 

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Shifting back after a few pedal revolutions sounds like the limit screw is too tight.

From the Ultegra Di2 dealers manual. DM-UL0001-02-ENG.pdf
Note that the lower limit (largest cog) limit screw is tightened until it's against the stopper. So--no extra play is needed, but see below for warnings about too-tight limits.

The high limit (smallest cog) needs one whole turn of the adjustment screw to allow for the brief over-shifting when going to a smaller cog.
From the manual: tighten the top-side stopper adjustment bolt until it touches the stopper at the position where the rear derailleur finally stopped. From this position, turn the top adjustment bolt counterclockwise one turn so that an over-stroke allowance can always be maintained.


--------------------------
A sidebar at the limit screw adjustment page:

Phenomenon that occurs due to an
excessively tightened adjustment bolt:

••Gears do not shift to the top/low gear.
(Even if you shift gears to the top or low
gear, the gear may shift back by one gear
after about 5 seconds.)

••Noise does not stop.

••Battery charge disappears quickly. (load is
being placed on the motor)

••The motor may be damaged. (irreparable)​
 

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I've run this combo. I'd still bet 5 to 1 that you have a bent hanger. For some reason, shimano cassettes are more forgiving than the sram red 30 tooth. Di2 is famous for bending hangers because of user error (shifting too many gears too fast).

I posted on this same problem and Wrench posted a similar response--maybe a years or so ago. It really hurts to admit that this ******* is usually right. Someday!
 

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'brifter' is f'ing stupid
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I've run this combo. I'd still bet 5 to 1 that you have a bent hanger. For some reason, shimano cassettes are more forgiving than the sram red 30 tooth. Di2 is famous for bending hangers because of user error (shifting too many gears too fast).

I posted on this same problem and Wrench posted a similar response--maybe a years or so ago. It really hurts to admit that this ******* is usually right. Someday!
Someday I won't be an ******* or...? I'll always be an *******, I have too much time in to change. :D
 

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... going from a 28t to a 30t should be 1-2 more links.SS-
Not quite. The chain only wraps half way around the cog, so there's only 1 more tooth of wrap, which is 1/2 link. One link is the smallest increment that chain length can be changed = 1"= set of inner and outer plates. If your chain is on the very limit on the 28, you might need to add 1 link, but that's pretty unlikely.
 

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That's why I said to check the chain length first. From my experience, granted that is pretty limited, when a bike comes with a 28t and a short cage the chain length is at the point were you can't put any bigger gearing on the back without adding to the chain length. Heck up until recently it wasn't recommended to run more than 28t on with a short cage. But it sounds like this is a moot point because of the previous posts about the limit screw.

SS-
 

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I've run this combo. I'd still bet 5 to 1 that you have a bent hanger. For some reason, shimano cassettes are more forgiving than the sram red 30 tooth. Di2 is famous for bending hangers because of user error (shifting too many gears too fast).

I posted on this same problem and Wrench posted a similar response--maybe a years or so ago. It really hurts to admit that this ******* is usually right. Someday!
So that's how I keep bending my hanger, just too much too fast..

Not that I am fast just moving gears 😜
 
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