masi61

The lead up to the cable breakage: I was on a lovely ride in the country and noticed that my rear derailleur shifting was not spot on like it should be. I was playing with my adjuster barrels (snugging up a bit of slack) which didn’t really help much. So I pulled over, shifted to my smallest (12 tooth) cog in the rear. I then tightened the down tube and derailleur adjuster barrels all the way to see if there was slack that needed to be pulled out of the cable. It wasn’t much but I was able to snug up about 1/8”. I restarted my ride (still not at the half way point - say 16 miles in) and noticed that now my Flight Deck LCD gear display was off synch by one cog on the gear read out. I continued my ride and was making my way to my girlfriend’s house (~47 miles in) and I felt the strands of the inner cable for my Dura Ace ST-7800 all give way in one big CRUNCH! Luckily I was in her platt and had a mostly flat road to her house in my 39x12 gear. It was obvious that the dreaded Shimano cable breaking inside the shifter scenario had occurred to me. Honestly, I was under the impression that the older, cable housing exiting outside the shifter in a gentle swoop to the down tube cable stop style (as opposed to the newer, under the tape design) was less prone to snapping off the cable barrel.

Anyway, I got rid of the shedded length of cable but now needed to extract the old broken cable barrel and any shredded bits remaining. I could use a lifeline here, fellow BF mechanics: what is my next course of action?

I am at at a loss about how to get under those 2 little cover plates. I will search of the exploded diagram and post a link to the German Shimano PDF file that saw once but have now misplaced....

https://si.shimano.com/pdfs/ev/EV-ST-7800-2258.pdf

trailangel

Your next course of action is.......GF

davidad

Shift to high gear (small cog) and try to push it out with a thin punch.

masi61

i think it is stuck. I can’t visualize the barrel. I’ve only got like 3 or 4 clicks instead of 9.

Iride01 

You got to get the reel into the setting for your high gear in order to get the cable end out. If not, you'll have to disassemble it. Can you pull on the cable as you click the small lever and get it to move?

Since you knew where to get the exploded view, I'll assume you know where to get the DM.

Perhaps if no real bicycle mechanics come to the rescue here, then call a shop. I've only had one frayed cable in an STI so far. I caught it before it became too big an issue.

shelbyfv

As mentioned above, you'll have to somehow get the shifter into highest gear if the cable end is still where it should be. If it has moved and is wedged somewhere else, it's going to be difficult or impossible to get it out. IIRC the 7800 does not have access panels like the newer shifters have. There isn't a lot you can disassemble with much hope of getting it back together. Tweezers, a small pick and patience....

masi61

Thanks for your reply. What “DM” stand for again?

I think there is no top down visibility of the barrel on the 7800 like there was on the 7700 that I have. It appears as if the shifter mechanism can be separated from the shifter body by some procedure.

I’ve not done this yet. Could anybody walk me through the procedure for separating the shifter mechanism from the shifter body? I’m thinking there is a very small metric set screw on the underside of the shifter body that plays a role in releasing the innards.

Iride01 

DM is Dealers Manual. Why I don't know, they generally are everything you'd want a user manual to be. However I forgot that your series being older won't have a DM available. Whether that is because there never was or they take them down, I can't say. Seems I only see DM's for current and recently superseded models on the shimano teck doc site

Here is the SI, service instructions which might give you some insight. They just aren't quite as informative as the DM's which go into maintenance and disassembly a tad more.

https://si.shimano.com/pdfs/si/SI-6JA0A-000-ENG.pdf

If you can't get the reel fully unwound, then you won't have the slot and holes lined up to remove the cable end and remaining cable. I've been thinking that when you say barrel, you are talking about the cable end. Or is it something else you mean?

Still, I only play mechanic on the forums. <grin> You'll have to hope a real one comes along as I haven't worked with STI's other than 105 5800 and Tiagra 4700. Certainly I have no tricks to get stubborn frayed ones out.

dedhed

https://si.shimano.com/pdfs/ev/EV-ST-7800-2258.pdf

masi61

Update: I was able to use a flashlight after it got dark last night and see the shards of broken cable poking about inside the shifter. I was having trouble downshifting the lever all the way due to this interference but I fiddled with a cut-off piece of cable wire and was able to push them through enough to get the shifter to finally click down, exposing the little zinc cable barrel head. I was now able to insert the extra bit of cable from the opposite side and shove the broken cable back out with all the broken cable strands still attached.

I will edit this post tonight and post a picture of the broken end of the cable that was extracted. Thanks for your replies everybody and your links to Shimano documents pertaining to the 7800 series, I appreciate it.