Shimano 6770 DI2 High Limit Screw Wont Turn

Bikergroves

Hi,

I recently replaced my worn out rear cassette and, when putting everything back together I noticed the chain would not shift up to the highest sprocket on the back.

Upon further investigation I noticed the high limit screw was stopping the rear mech arm from fully extending all the way to the top

I've tried to unscrew the limit screw but my 2mm Allen key just turned around inside. It's was almost as of the end of the bolt has been snapped off where the allen key is usually inserted. There was no head to it and nothing for the allen key to grip on to.

It looks different to the lower limit screw which I can easily adjust as normal.

I've attached some pictures.

Could someone tell me if a) this is normal and i'm doing something wrong or b) the screw is dead and needs to be replaced

Im using Shimano DI2 6770, the first incantation with the ugly battery that sits under the bottom bracket.

Answers much appreciated

Ben6899

The head is on the other end.

Bikergroves

Ah, how do I go about turning the head? It's flat and doesn't have an Allen key hole.

First.Aspect

The adjustment screw is in the wrong way up isn't it? Meaning that the recess for your allen key is at the other end. That's not something I've ever seen before, I must say.

keef66

The exploded view on shimano tech docs shows them arranged like yours, one one way and the other the opposite way.

You sure the head doesn't have a socket in it? Is it just filled with muck?

Edited to add that the illustrations in the Dealer manual show them both the same way round and being adjusted with a 2mm allen key

First.Aspect

keef66 wrote:

The exploded view on shimano tech docs shows them arranged like yours, one one way and the other the opposite way.

You sure the head doesn't have a socket in it? Is it just filled with muck?

Edited to add that the illustrations in the Dealer manual show them both the same way round and being adjusted with a 2mm allen key

I think you are aboslutely right. I have found some pics online showing this also.

The wider head at the other end is just flat - you can see by zooming in to some of the photos. I also think you are right that part of the inside of the threded end should have the required hexagonal cross section. Nothing has snapped, its just dirty.

I'd try all the usual tricks like penetrating oil, using another allen key (there might be some manufacturing tolerances) or wrapping some teflon tape or something like that around the allen key and really jamming it in there, before totally giving up on it. Or even mole grips on the flat end, just get get it moving again. They will bite and cause some damage, but hopefully just cosmetic.

Oh, and if it is furred up, get the mech away from the end stop before trying to move it.

If its completely rounded out inside the hollow end, it might need careful use of mole grips (to avoid damaging the rest of the derailleur) and a replacement. Again, try to turn it from the fat end, because you don't want to damage the threads which will pass through the bracket.

Bikergroves

Thanks for the replies. Much appreciated.

rafletcher

And it is an Allen key is it - Torx seem unaccountable popular these days....