soundandmotion

searched a bit, came up with a bunch of relatively similar posts, but mine is a little unique.
reposted from another forum:

"my left shifter is behaving wonky
it's dura ace 7800, double
my last one was officially busted, so i ordered a used one on the internet for cheap, cause dude said it worked fine despite some cosmetic damage (which i was able to fix)
i suspect i got ripped off
but i want to make sure i'm not just a total idiot before i invest in a new replacement

here's the deal:

i install the shifter, get all the cables hooked up and start adjusting the derailleur.
during this process i've got the chain sitting on the small chain ring, and the derailleur cage is right where it needs to be over that.
attach the cable and everything is cool, shift up to the high gear and it works perfectly, it's all aligned right and everything.
then i shift back down and it pulls some weak **** and shifts like a third of the distance back toward the low gear and won't go any further.
i can shift back and forth between these two levels but they vary by like a few millimeters.

my last shifter had a similar problem where it would shift up and then not back down, but it would just not move once it was in the higher gear. this one reliably does make a shift, it's just not an acceptable distance, so i'm hoping it's not toast.
no amount of feathering makes it acceptable. i can adjust the derailleur in various ways, but the range between the top and bottom positions is not large enough to cause the chain to shift in both directions.
the initial cable tension is not too high, so i don't think that's a problem (and if it was, i don't think it would sit in the lower gear so well initially)
and once i shift up and try to shift back down, the cable tension is pretty high, so i don't think it's a derailleur spring problem.

any ideas about something i could be doing wrong, or is my shifter just screwed up?"

similar to the relatively famous shimano sti shifter problem, only mine actually does shift, just... not very much.
i would love to just be an idiot doing something stupid here, and not need to buy a new shifter.

operator

Make sure you know how to or are doing the procedure to adjust it correctly before blaming the shifter:
https://www.parktool.com/repair/readhowto.asp?id=75

Also, are you positive the cable head is engaged properly and that the cable isn't fraying inside? Is the housing new? Cable new?

Al1943

My thoughts are all just "possibilities".
1) Kinked cable?
2) Dirty cable housing, is it new or old?
3) Dirty shifter mechanism, have you tried the well known WD40 treatment.
4) I would never buy used STI shifters off the net.

curbtender

+2 on the cable housing. Has it been replaced?

davidad

Make sure the deraileur is clean and lubed. They can get gumed up from sports drinks dripping on them.

soundandmotion

yep cable and housing is new, though i'll take it apart and make sure it's not fraying anyways. i'll also clean the derailleur and try the wd40 method in a little bit and report back.

i blamed the shifter because the last one had a similar problem and although i'm a little new to wrenching i have a pretty good idea how to adjust a derailleur.

buying a used shimano sti was a dumb idea, but the picture said it worked fine and was being replaced due to cosmetic damage on the front plate and hood.
so i figured a fred was flipping it on ebay because their dura ace wasn't shiny anymore.
i picked it up for 30 dollars, put the pristine hood and front plate from my old shifter on and thought it was good as new. figured i'd risk the 30 bucks to get a working replacement before shelling out 200 or so.

Al1943

Try hosing the shifters out with lots of WD40. That's how I fixed my 1998 Dura-Ace shifters and they still work perfectly 8 years later.

Al

soundandmotion

i pronounce thee shifter deceased.

replaced cables & housing just for the hell of it
wd40'd the shifter to kingdom come

reattached the cable and tried to shift a few times, with me just holding the cable, not hooked up to the derailleur.
now the thing isn't reliably shifting at all and when it does, it's still like 3 mm.

looks like i need to replace the whole thing.

Ex Pres 

Cable friction
Too tight a bend somewhere.
Without a cable attached do you hear clicks? Edit: I should read better. 9 up and then 9 down?

soundandmotion

wrong side shifter
and i replaced the cables

i doubt it's cable tension, but i'll see if i can get it to do anything without it being bent at all

soundandmotion

does anybody know if i can use a triple shifter for my double derailleur/chainrings ?
on the lower end models it says you can, but it doesn't clearly say that the DA triple shifter will work for a double

soundandmotion

with absolutely no cable friction it's back to relatively reliably shifting a uselessly small amount

Retro Grouch 

Are you sure that you had it in the lowest gear position at the start?

I'm thinking that shifter should have a couple of index positions. If you set it up with the shifter in one of the intermediate positions it'll act just the way you indicated. Don't ask me how I know, lets just leave it at "I've seen that done."