Dura ace di2 rubbing in big ring

tonyhogg

Experiencing lots of chain rub on the front derailier when in the big ring and the Middle of the cassette, it's noise free in the last 5 smallest gears but going back up the cassette all 6 gears rub lots, it's just doesn't appear to be trimming correctly? Small ring is absolutely perfect. It's a 52/36 semi compact 11-28.

964cup

Have you set up the trim? Put the bike in big-big, hold down the button under junction A until the solid red light comes on, then use the LH shifter to step the FD inwards (repeatedly pressing as if to shift to the small ring) until you get no chain rub. Then hold the button under junction A down until the red light goes out.

CiB

If the FD is rubbing the auto trim might not be kicking in when it should. I have Ultegra not DA so it may differ, but to set it on that it's a simple case of tweaking the upper & lower limit screws with an Allen key in line with the instructions to set the chain guide in the right place relative to the rings.

tonyhogg

I'm sure once the chain rub is removed from its current location it'll appear somewhere else, I've had nothing but problems with 11sp and nobody else complains about it???

Bar Shaker

The latest Di2 has trim adjustment for the FD, as 964Cup has said. Putting it into adjustment mode and setting this yourself is really easy. If it won't adjust outwards for the lower gears, it may be that the limit screw has been set much too short. You don't actually need limit screws with Di2, as it can't go beyond where it knows the end of it's travel to be. It should have been set up correctly for you though and this is a problem with the shop, not with 11 speed DA Di2.

Nobody else complains because once it has been set up, it is perfect and it stays perfect. If the shop you bought it from can't do it, you should learn to do it yourself or take it somewhere else, where they can do it.

Pokerface

Bar Shaker wrote:

You don't actually need limit screws with Di2, as it can't go beyond where it knows the end of it's travel to be. It should have been set up correctly for you though and this is a problem with the shop, not with 11 speed DA Di2.

I find with mine, if the limit screws aren't set properly, I can actually shift the chain off the outside of the big ring. So the limit screw stops this from happening.

I use the limit screw to adjust the front mech so that there is just a few mm of space between the mech and the ring when in your biggest gear.

CiB

Pokerface wrote:

Bar Shaker wrote:

You don't actually need limit screws with Di2, as it can't go beyond where it knows the end of it's travel to be. It should have been set up correctly for you though and this is a problem with the shop, not with 11 speed DA Di2.

I find with mine, if the limit screws aren't set properly, I can actually shift the chain off the outside of the big ring. So the limit screw stops this from happening.

I use the limit screw to adjust the front mech so that there is just a few mm of space between the mech and the ring when in your biggest gear.

Quite right. Unless all frames have exactly the same offset from the FD fitting to the rings you're going to need limit screws. The limit screws on mine (Ultegra) needed adjusting when I moved it to the identical warranty replacement frame; shifting was dire until I did.

964cup

The limit screws are necessary; Di2 deliberately over-shifts to ensure the chain moves, then trims back. The limit screws control how far. This is especially true of the lower limit screw on the RD, and the upper limit screw on the FD. It's why you screw the lower limit screw on the RD in until it touches the stop, with the mech in the smallest cog, then back it off exactly one rotation to allow the overshift.

Bar Shaker

I have my limits wound right off. The over shifts work perfectly and trim back before the chain can fall off. This is written into the software and very well understood. The timing is perfect and the chain not falling off has nothing to do with the limit screws, if you have the FD indexed perfectly.

It is a joy to watch it do this and it is something that cannot be replicated on ye olde caybles.

Pokerface

Bar Shaker wrote:

I have my limits wound right off. The over shifts work perfectly and trim back before the chain can fall off. This is written into the software and very well understood. The timing is perfect and the chain not falling off has nothing to do with the limit screws, if you have the FD indexed perfectly.

I have 5 different bikes, all with Di2. I can assure you that the limits screws are indeed necessary. It may work on YOUR bike, but it does not work the same one all bikes. Cranksets are spaced differently and what works for one won't work for all.

There is nothing in the software that prevents shipping the chain off the big ring. If there were, they wouldn't have limit screws.

I have definitely managed to shift the chain off the big ring before setting the limits properly. Please don't attempt to 'educate' people that the limit screws aren't necessary. They are.

Bar Shaker

When you change from small ring to big ring, the FD moves past the large chain ring, waits and then moves back. It is this action that creates perfect FD shifts. Because it moves back as the chain catches, it doesn't derail the chain off the outside.

It will derail off the outside if it is not indexed to the big ring when in its resting position.

You can stop it having this wonderful 'over shift' action by using the limit screws to stop the mech going beyond the optimum resting position on the large chain ring, but why would you want to???

I only have two Di2 bikes in my garage, a Boardman SLR and a Bianchi Infinito. Two very different bikes but both get ridden 12 months a year and do approx 2500 miles a year. They are both perfectly set up and have no limit screw restrictions on the front or back mechs. Neither have ever thrown a chain, front or back... because the mechs are both indexed perfectly.

I would say that if you think where the mech ends up can vary on shifts, or if you think that the motor needs to be stopped before it finds its target stop position, you haven't really understood how Di2 and stepper motors work. If you drive the motors against limit screws, they try to find their indexed position for a while, before giving up. I would think that having the motors grind against limit positions that you have decided to impose won't do the life of the motors or the life of your battery much good, but who am I to educate you?

Enjoy your Di2 bikes... all 5 of them.

Pokerface

Bar Shaker wrote:

When you change from small ring to big ring, the FD moves past the large chain ring, waits and then moves back. It is this action that creates perfect FD shifts. Because it moves back as the chain catches, it doesn't derail the chain off the outside.

I'll try and use small words so you understand.

It is possible for the chain to go off the outside of the big ring. The limit screw will determine how far away from the frame the front mech will pull across (and pause) BEFORE moving back again. Too far, and the chain can fall of BEFORE the mech moves back. See how that works?

Here's a pretty basic video that explains how to adjust the front mech: https://www.youtube.com/watch?v=PU2kQp9IeBc

Having the rear indexed properly is no guarantee that the front will work correctly. Especially when it comes to overshifting the front from small to big.

But hey - don't believe me. Believe Shimano. Try reading their manual. Pages 55-57: http://si.shimano.com/php/download.php? ... 00-ENG.pdf


As you were.

Bar Shaker

Those instructions are for indexing the FD. You aren't setting limit screws (read the manual), the screws move the whole body and the cage until it is in the correct alignment. Every bike needs these set up correctly when the FD is fitted.

On 6870 you can then fine tune the index with the buttons on the shifter. On earlier versions you had to get it right mechanically.

Perhaps you just thought they were limit screws as they have a vague similarity to the limit screws on cable mechs.

Pokerface wrote:

I'll try and use small words so you understand.

Keyboards have a habit of making some people say things they wouldn't dream of saying if they were stood in front of someone, so I'll ignore that comment.

bernithebiker

As I have a Di2 groupset in the post and I've never set one up before, would be nice to know who's right!

Pokerface

Bar Shaker wrote:

Those instructions are for indexing the FD. You aren't setting limit screws (read the manual), the screws move the whole body and the cage until it is in the correct alignment. Every bike needs these set up correctly when the FD is fitted.

On 6870 you can then fine tune the index with the buttons on the shifter. On earlier versions you had to get it right mechanically.

Perhaps you just thought they were limit screws as they have a vague similarity to the limit screws on cable mechs.

Pokerface wrote:

I'll try and use small words so you understand.

Keyboards have a habit of making some people say things they wouldn't dream of saying if they were stood in front of someone, so I'll ignore that comment.

I can assure you I'd still call you an idiot if you were stood in front of me. But I digress.

The screws on the front mech (which are indeed limit screws) don't move the whole front mech. They adjust the range of movement. You can adjust how far in AND out the mech moves (independently of each other). I am also aware that on the new Ultegra and Dura Ace mechs you can now make fine adjustments via the shifters.

Even if you don't agree what the screws are actually called - the function remains the same and confirms what I said previously - you can indeed ship the chain off the outside of the big ring if the mech isn't set up correctly. This isn't the same as having it indexed correctly (which will prevent the chain rubbing the mech).

Pokerface

I'll post this last link and leave it at that as it should pretty much clear everything up: http://bike.shimano.com/publish/content ... faq_s.html

It's a DI2 Troubleshooting page from SHIMANO.

Read the part that says "Symptom: My chain is falling off my chainring when shifting"

And where it says:

Check your front derailleur limit screws
o High limit—0.5 to 1 mm between derailleur cage and chain while on large chainring.
o Low limit—0.5 to 1 mm between derailleur cage and chain while on small chainring.



Please once again note - this is for Di2. Not mechanical.