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.

EDIT: November 2020

Short answer: I kept fiddling with it, and eventually it all snapped together nicely. So there is no magic orientation, you'll know when everything is correctly assembled. The answers below are much more methodical, and helpful.

  • 2
    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, 2017 at 1:02
  • 1
    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, 2017 at 2:12
  • 1
    I have this exact same part and when reassembling, yes it is tricky but I fiddle around for a bit and it just goes together
    – Vorsprung
    Sep 30, 2020 at 13:23

3 Answers 3


You have probably resolved your problem, but others may encounter it; I did.

Number the 6 parts in your photographs from left to right so they correspond to the exploded sketch: 8--the nut; 7 and 7a (7 is the mount that enters the bar; 7a is the notched, cylindrical disk that is a separate piece from the mount.); 6--the single tabbed notched washer; 5--the double tabbed washer; 4--the lever; and 321-- the pronged ratchet mech, conical plastic cover, and bolt.

Washer 5 rests with the tabs against either end of the raised segment of 4 (lower photo). Insert 321 into the back side of 4. Place 6 on top of 5 with the tab up and notches aligned with the prongs of 321. Place 7a on top. The tab shown at the top of 7 in the sketch fits between the single tab and the raised segment. All the parts are “fiddly” but will fit together only one way; if any parts are canted even slightly, try again. I found it helpful to put a dot of nail polish on 321 and 7a in way of the single tab of 6.

Install the parts on the mount, tighten the bolt, and check the function.

  • Welcome to SE - that's a great and helpful first answer. Keep it up! You can browse the tour to learn a bit more how Stackexchange is organised. I look forward to any future answers.
    – Criggie
    Sep 29, 2020 at 2:21
  • Thank you Cap'n! These are really good instructions. I eventually took my Rubiks Cube approach to it (ie random orientations) and it all just clicked together. Your answer should speed things along for the next person.
    – idoimaging
    Nov 4, 2020 at 0:13

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.

  • 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, 2018 at 17:44

I managed to get mine together as well - it's difficult, I had to push the pedal with my feet to change gears upwards, while lifting the bike up with my teeth, because both of my hands were holding the shifter.

When you look inside part #3, there's a particular way part #8 fits in there. Get them aligned (I had to tighten the cable, lift the lever) for that.

  • Welcome, I suggest to take the tour to see how this site works. Please write answers that are really answers that bring something new, not just a Thank you. You can thank by upvoting the question, the answers. Once you get a few reputation points you can also comment under any post. As it stands, your answer may receive flags to be deleted or downvotes because the new information is hidden. Apr 7, 2021 at 9:35

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