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I have a Shimano (I think Dura Ace) 10-speed rear shifter from around 2008, it came on the aero bars of a Cervelo P2-SL. Like a genius I took it apart today and I cannot for the life of me work out how it goes back together. Not much on the web though many people refer to a '105' bar end shifter though mine says '10S' (10 speed), it looks a lot like '105' so I think that is the cause of the confusion.

Here are the constituent parts:

In orientation of Shimano exploded view

And with the four rightmost parts turned around:

Opposite side

I haven't found the exact part on Shimano tech docs. The closest I find is the SL-BS78, but the exploded view PDF makes no mention of the two irregularly-shaped washers in the centre of my pictures, and they're my problem. I did find what seems to be the same mechanism in the SL-7900 downtube shifter, relevant bit shown here:

SL-7900 exploded view

It's the two washers that are killing me. The rightmost one (part 5 'Stopper washer' in the EV) fits in the lever nicely, but the leftmost one (part 6, 'Spacer for rear'), while it does sit over the mounting stud, freely rotates when it seems it should engage on something. It has 6 tabs that correspond to the mount, and seem to correspond to the 6 lugs on the SIS unit (lower photo, right), but it doesn't fit over or inside any part during assembly. It slides around and it seems it needs to line up with the SIS unit somehow.

My washer 6 has a tab (lower photo) that goes toward the mount. The 7900 EV doesn't show that, but the Service Instructions show its orientation, which I'm following. It's just that I can't get it to line up with or over the SIS unit.

enter image description here

Help me, wise interwebs.

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    Risky idea - but do you have one on the other side? Could you carefully take that one apart and see how it is assembled too? – Criggie Nov 6 '17 at 1:02
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    Good suggestion! However the front shifter is not indexed and the exploded view shows it is much simpler and doesn't have either of those two parts. But thanks for the idea. – idoimaging Nov 6 '17 at 2:12
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The black grease tarnishing on your washer number five in image one indicates to me that it was up positioned next to the black greased face of your component number seven

Which would be opposite of the install instructions - but as you previously stated, and from the diagram and images you are not working with the correct component diagram

try reversing washers five and six and facing the black greased sides of the respective components unto each other and see if that makes it fit together.

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  • Thanks for the advice! I think the washers were anodised rather than greased, but yes the colours were significant. As it happens, I tried a few more orientations the next day and of course it all just snapped together. I don't recall the winning orientation but if someone comes across this thread, just know that when the orientation is correct, the washers do sit nice and tight before you put it together. So it's not like you have to have everything in one magic place and put it together carefully. – idoimaging Jan 31 '18 at 17:44

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