My Ultegra sti level will not down shift so it is stuck on the big chainring. At first the lever seemed jamed but now it moves but has no effect on the F.mech.
It jammed last week but I managed to free it, but now it seems well an truely stuck.
Is it possible to fix this or will I have to replace the whole shifter?
Without seeing the shifter itself, I’obviously couldn’t say for sure but:
Sometimes the problem is with the cable, not the shifter. If the cable isn’t seated all the way in the shifter, or if it hasn’t been cleaned and lubed, or if it isn’t attached to the derailleur properly, you will have problems. If you’re stuck in the big chainring, either your shifter isn’t releasing cable tension to allow the derailleur to move back in, or the derailleur itself isn’t moving. Without taking it apart to see what’s sticking, you won’t know what you have to fix or replace.
Shift back up in the big chainring. Check the top of the shifter pivot to see you did that. Then hold the brake lever firm with one hand (make sure it doesn’t move laterally with the smaller lever), and then move that smaller lever all the way to the side. When you do this, hold or watch that front derailleur wire to see if any tension is released.
Get a dt shifter to replace that unsightly STI unit. Just kidding.
I have undone the cable at the mech and it is diffinatley a problem with the shifter it will not release the cable to line it up with the hole to pull the cable out. I don’t know if the cable is just jamed or if there is something more drasticly wrong.
It looks like tomorrows TT might have to be done in the big ring only 
It could be something broken, or it could be gummed up internals. My Ultegra STI started having shifting problems after about 5 years. The front wouldn’t shift to the small ring and rear wouldn’t shift to smaller cogs - especially in cold weather. If I pushed forward as I pushed the small lever inward, it would usu. shift. I cleaned the levers out with degreasing spray and they’ve been working fine since.
I have undone the cable at the mech and it is diffinatley a problem with the shifter it will not release the cable to line it up with the hole to pull the cable out. I don’t know if the cable is just jamed or if there is something more drasticly wrong.
I had a similar problem with 9-speed DA and it sounds to me like the phillips head screw that keps the shift lever tight against the shifter body has come loose sufficiently and now the cam mechanism is not meshing properly. The first time I ran up against this I disasembled the entire shifter only to find that the problem can be solved without need of any disassembly. The screw in question is sort of hidden as it is located just below the point at which the shift lever attaches/pivots to the main body. To check to see if the screw is loose, Use one hand to push bot the brake and shifter lever inwards to the limit of its throw and inspect the back side of the lever for a small phillips head screw and see if it is tight. If it is loose, tighten it and most likley you will see a resolution to the problem. I blieve that Shimano issued a service buletin that included replacing the screw in question with one that had thread lock compound applied to prevent a repeat occurence.