Forum home Road cycling forum Workshop

Dura Ace shifter not shifting down

bing gordonbing gordon Posts: 662
edited April 2017 in Workshop
I went out this morning and after about 5 miles my right censored stopped shifting up through the gears and was stuck (Dura Ace 7900 right side). I tried in vain to sort it but I had to ride home in the one gear.
I looked around and the net and a few remedies was clean grease/gunk but WD40 didn't work. It clicks once but that's it so I took it off to take a proper look.
It's like the metal teeth are not catching. To me it looks bent so I posted a picture of the inside. Is it my eyes or is the small catch for the teeth bent out therefore not locking into the teeth ?(red arrow highlighting it)
any ideas would be greatly appreciated

54wqgw.jpg

Posts

  • bing gordonbing gordon Posts: 662
    sqja.jpg
  • Ben6899Ben6899 Posts: 9,096
    The catch is definitely twisted out of shape/position. Crikey, how has that happened?
    Ben

    Bikes: Donhou DSS4 Custom | Condor Italia RC | Gios Megalite | Dolan Preffisio | Giant Bowery '76
    Instagram: https://www.instagram.com/ben_h_ppcc/
    Flickr: https://www.flickr.com/photos/[email protected]/
  • bing gordonbing gordon Posts: 662
    God only knows, I bought them off here awhile back but never installed them. I haven't done much mileage on them a few 100 if that so it must only have happened by the previous owner and it's all gone pear shaped on me. Is it something I can fix/bend back or send it into a shop ?. I can only find one video for a strip down on a 6700 Ultegra

    ..........................

    I took another look and compared it with the youtube strip down of an Ultegra shifter but it looks abit different. What seems to be the issue is, force probably when braking. I think something like a long screw or a pin is missing and the whole mechanism is moving when braking and it's bent it up over time.
    I've made a short video showing the movement when I apply pressure to the brake lever. The top part of the catch moves backwards forcing the catch that locks onto the teeth to moving in a slight upward motion but when braking heavily I can imagine this going right up. Now that I think back to when I first installed them the right side braking lever always needed some pulling back to brake even with new cables and housing as if it were an adjustment but it seems now not to be the case. I've stuck a tooth pick in the bottom were there's a hole that goes right up through the centre of the catch and cogs area of the shifter just to highlight it.

    Does anyone know if a screw or pin should be going up there holding it all in place ?. On the Ultegra video there a screw going up he unloosens to release it all
    https://vimeo.com/214286678
  • Ben6899Ben6899 Posts: 9,096
    Does this video help at all?

    https://www.youtube.com/watch?v=wJj6dASBMN0&t=76s

    I haven't watched it all the way through, but he quotes DA7900.
    Ben

    Bikes: Donhou DSS4 Custom | Condor Italia RC | Gios Megalite | Dolan Preffisio | Giant Bowery '76
    Instagram: https://www.instagram.com/ben_h_ppcc/
    Flickr: https://www.flickr.com/photos/[email protected]/
  • jgsijgsi Posts: 5,031
    I dont think you have much to lose if you strip down yourself and re assemble, with the unit fault actually thus rectified. Hopefully.
    Quite a few mugs of tea job methinks . Not to be rushed.
  • 6wheels6wheels Posts: 411
    http://i1070.photobucket.com/albums/u50 ... oizgnx.jpg

    Looks as though the pieces marked red should be one part, looking closely the teal marker indicates a fracture.
  • bing gordonbing gordon Posts: 662
    6wheels wrote:
    http://i1070.photobucket.com/albums/u500/77712/modInked54wqgw_LI_zpsbaoizgnx.jpg

    Looks as though the pieces marked red should be one part, looking closely the teal marker indicates a fracture.

    Thnaks for that but If you look at ben6899's video from youtube and go to 1:09 I think the video shows them moving independently. What I can't figure out is if there's a screw bolt on the underside that allows it all to come to bits, were I stuck the toothpick as a guide.
    The video shows him undoing a screw from the underneath , this is at 1:21. Mine doesn't have anything nut there and the hole is no were near the size of that in the video for the Ultegra
  • Ben6899Ben6899 Posts: 9,096
    The LH shifter, despite only having two shifts, will be built the same. It's probably worth a look inside it, for the purpose of comparisons.
    Ben

    Bikes: Donhou DSS4 Custom | Condor Italia RC | Gios Megalite | Dolan Preffisio | Giant Bowery '76
    Instagram: https://www.instagram.com/ben_h_ppcc/
    Flickr: https://www.flickr.com/photos/[email protected]/
  • bing gordonbing gordon Posts: 662
    I think that's my best option, I cant see how it all comes apart. Unlike the video for the Ultegra this doesn't have a locking nut from the underneath holding the mechanism all in place.

    If someone knows any shop who repairs these shifters please let me know. I'm scared of making it worse and their not cheap
  • bing gordonbing gordon Posts: 662
    I spent last night hoping I could fix it for today's ride, I used the ST-6700 disassembly video as reference but I never even got off the ground.
    For starters, as in the video there's no screw on the underside that releases the catch and metal cogs mechanism and after a further examination there's no bolts or screws I can see that release any moving parts. I tried to dislodge the carbon arm by pushing on the locking pin but that wouldn't budge. It's then I noticed you need 2 x tools A & B to release the "E" rings.

    I'm all for having a go repairing but this is kinda stuff is like a swiss clock with no release screws or clips that I can see. I think it will be sold as a spares and repairs as the overall condition of the parts and in v.g condition , I'd say 8/10 and someone who knows what their doing will have a play around and no doubt sort.
  • jgsijgsi Posts: 5,031
    Worth contacting a Shimano Service Centre? These shifters still retail at over £160 each if you are lucky to find one.
    http://cycle.shimano-eu.com/content/seh ... enter.html
  • bing gordonbing gordon Posts: 662
    Your right, there's one not far from me about 10 mile away but I need the bike asap so I'm going to sell it with some other bits and buy a new one. Someone with more know and time will canabilise it or repair it.

    The carbon shifter arm body on it's own is worth £80 and the original chrome face plate £20 so someone with a damaged 7900 of their own could make use of it. I will advertise it as a spares repairs.

    If it were easier to take apart then I would have a go myself but without any actual 7900's breakdown vid's or tut's it can only go one way ......pear shaped , thanks all but I give up :)
  • bing gordonbing gordon Posts: 662
    And just as a follow up, I took up JGSI's advise and emailed the vast majority of Shimano UK service centre's and those that got back all said the same thing. You can't get mechanism parts and they are a nightmare to fix. They said the best option was to simply buy a new one.

    Not on your Nelly, so if it's knackered and no wants to buy it for spares/repairs I have nothing to lose bar a few hours of my time so it's down for a Bing autopsy this afternoon. I have ordered both A & B E-Ring tools costing a £10 to dismantle it and then attempt to repair it.
    I will try and take snap shots and videos throughout the process and hopefully someone can help me out or I can help countless others who are in the same boat
  • bing gordonbing gordon Posts: 662
    2nd follow up
    FIXED !!,
    I ordered both A & B e-ring tools but to be honest you don't need the small spanner tool. The bits I had to suss out was how the how centre cogs came out. Unlike the Ultegra video the 7900 is slightly different in that you need a small flat headed screw driver that fits across the width of a slot on the underside (were I had the tooth pick in the picture) then turn to release a locking nut on the top.
    All the parts slot into each other so there's nothing much you cant screw up. The 7900 also doesn't have the small spring as shown in the video, the one on the right hand side.
    The way to do it is, every time you put a cog in place push the nut up it keeps it in place for the next one. but the hardest part which probably took an hour ot get right was the very bottom spring underneath white plastic cogs. This doesn't line up anything like the Ultegra and needs pulling back for tension. I had to have a break as I was losing it but eventually when I got the nack it was not that bad.
    The problem was, the catch plate as highlighted in the picture with the red arrow, it was bent back so it weren't catching the teeth when moving up gears. I took that apart springs the lot and tapped it gently with a hammer till I got it as best I could.
    Anyway only time will tell but after a bit of grease it's moving as good as ever. I was lucky simply because no parts were damaged beyond repair. The biggest hurdle in repairing a 7900 shifter is parts. These are rarer than fresh dinosaur poo so if a spring or cog is knackered you've had it unless you can find a scrapper somewhere and cannibalise it for parts.
    if you need any pics just ask I've loads showing the inner workings but no video as you need 7 hands to do the job.
  • lesfirthlesfirth Posts: 1,227
    2nd follow up
    FIXED !!,

    Well done!
  • bing gordonbing gordon Posts: 662
    Thanks oh and one last thing ,

    On the very underside of the main white cog body there's a ribbon cable that attaches from the cog main body back through the main plastic body to the top oof the shifter so you can add the flightdeck wireless system.
    This tiny cable hinders you no end when your trying to set the spring back in place. The cables a nightmare to get back into its slot the you have to spin the spring to get it under tension which is nigh impossible as the cable seriously restricts any movement.
    .Considering I've never use flightdeck wireless and never will I removed ththe,cable and made the reinstalling 20 times easier. I did try with it in but gave up after 2hrs of trying
  • svettysvetty Posts: 1,904
    Chapeau. You must have good eyesight and shed loads of patience!
    FFS! Harden up and grow a pair :D
  • bing gordonbing gordon Posts: 662
    It comes with age along with the lack money for a new one. I've tinkered for years with small components, small circuitry boards and mobiles but never watches and cogs and I had nothing to lose.

    Every component has a certain way they go back in. In the vast majority they make it so there's only one way round they can go back in but the problem with shifters and cogs is in which order they go.The video the guy does for the Ultegra shifter rip down was a massive help but certain things on the ST-7900 I had to figure out for myself.

    I'm not sure how long it will last hopefully for a good while but I wouldn't be fazed doing it again. If I had parts I would make a side line/pocket money out of it but the lack of any parts would put paid to that even broken ones are hard to come by
Sign In or Register to comment.