retired358

I have a Shimano ST-7700 left/front brifter which does not shift properly. The large lever works fine (shifting from the small to large chain ring.) However, the small lever (down shifting from the large to small chain ring) will not shift. The reason is that when pressing the small lever, the large lever also moves, preventing the small lever from completing the shift. If one holds the large lever to keep it from moving when shifting the small lever, it works fine. Everything has been flushed so that is not the issue. My bike shop does not have a clue.

Has anyone else had this issue and was able to fix the problem. If so, would appreciate any advice.

Thank you in advance.

daverup 

This thread has been useful in overhauling old Shimano brifters,
https://www.bikeforums.net/bicycle-m...ti-levers.html

fishboat

There's lots of videos on the web about this..I'd try it first..

dedhed

https://si.shimano.com/pdfs/si/SI-6BD0C-000-00-ENG.pdf

retired358

Thank all who responded. However, unless I missed it, the advice all related to gummed up shifters. As I think I mentioned, this not the problem which I have/was asking advice for.

My issue is simple that when trying to shift down (small left lever), the large lever moves as well and it will not release. It will release/shift down if I hold the large lever to keep it from moving.

Has anyone had this issue/found a solution?

Davet

Have you tried flushing/relubing the shifter internals? Old and gunked up grease is most often the problem with misbehaving shifters. Try it first. WD40 the internal mechanism, work the shifters multiple times, then use Tri-Flow or something similar. Who knows, it might work and it’s very quick and easy to do.

dedhed

If you look at this document they show you how to disassemble it and maybe you can see if you find anything amiss.
https://si.shimano.com/pdfs/si/SI-6BD0C-000-00-ENG.pdf

Crankycrank

A longshot but have you checked to see if the shift cable is starting to fray at the shifter? I recommend removing the cable for inspection as it isn't always easy to see installed. Could be a piece of cable broke off and is jamming the shifter. Of course something else could be broken in the mechanism but check the cable first. Check YouTube for 7700 shifter repair/assembly.

retired358

Thanks. Cable is new. Tried replacing cables three times....same issue

retired358

Yes, I flushed it several times. My bike shop did the same. I have flushed shifters previously to successfully remove gunk so I know how to do this...but that is not the solution in this case.

retired358

Since it (the small lever) shifts fine if I gently hold the large lever (to keep it from moving), I would think it is not gunk, dried lubricant nor an issue with the cable.

daverup 

Some of the old dry grease I've removed from Shimano brifters would not have been removed by flushing. It freezes the pawls preventing them from functioning. Scraping out the dried solid grease, then penetrating oil on the pivots should release them. You won't know for sure unless you tear them down.
Good luck

Russ Roth

Check the backside of the levers near the top of the smaller lever, there may be a small hole that a tiny screw can go into, if the lever has one there'll be one on the right lever in a mirror location. Can't remember which generation(s) of levers had this little screw but if it fell out it allowed one lever to work fine and the other to only shift when the other lever was held. It should be visible without having to move the hood.

canklecat

This...

...some old greases harden into a substance resembling brittle plastic that defies being flushed out or dissolved.

I've overhauled older German airguns and cameras that appeared to use the same distinctive green grease (not Phil's or marine grease, which doesn't harden the same way). The only way to dislodge the stuff was to disassemble the mechanisms and physically pick it out with various tools. In some cases I had to use metal dental picks. Other times I could get away with softer picks made of plastic or wood.

I've had a couple of sets of DA 7402 brifters on the workbench since last summer, waiting for me to finally get that round tuit and install them. The set that arrived in very good condition responded nicely to flushing with penetrating solvent and WD-40. Every few weeks I'd hit it again with penetrating oil and WD-40. I just checked it again and since the last time I looked (a few months ago) I can see more drainage that's roughly the consistency of phlegm, but much less of it than when I first got it. It seems to click through without problems but I won't know for sure until I install it on a bike.

The other set... didn't respond well. It was badly worn, pitted and probably good for parts only -- which I knew when I bought them, so the condition wasn't a problem. I intended that set only to cannibalize for spares to support the good DA 7402 set. It appears to have been very heavily used and the pitting appears to be from years of sweat, possibly combined with other contaminants -- spilled electrolytes, who knows. I've flushed it several times, occasionally dislodging some chunks of calcified lube that appeared to have congealed with salts from sweat and electrolytes. When I peer inside I can see other debris that won't flush so eventually it'll need to be disassembled. It's probably so worn that it'll never shift cleanly. But it should still be okay for salvaging a few parts.

I've seen this before in bikes used by racers, in headsets and even rear hubs. Over time salts from sweat and drooled electrolytes, road debris contamination from rain rides, etc., seep into nooks and crannies. The liquid dries, leaving behind a crust that resembles lime scale.

BTW, there's a Facebook group that's a pretty good resource for tips on older Shimano STI shifter maintenance. I'm not sure whether the group admin still offers repair services, but there are plenty of tips posted in the group.

Iride01 

They do just wear out. Maybe something new and better looking is in your future.

I always thought the cable coming out of them looked too much like those arrows we used to wear on our heads for Halloween to make others think we'd been shot in the head. Maybe a very small part of why I stayed with downtube shifters till 105 5800 came along.

Modern STI's look much nicer.

But if it's not a frayed cable, then I'd check for cables binding somewhere, maybe gummed up in the housings. Or perhaps a broken spring in the DR.

retired358

Russ Roth: Thanks for the tip on the potential for a missing screw...I will check that tomorrow.

There have been a lot of responses relating to dried lube or frayed cables...but, if either of these were the cause of the problem, then I do not see how it would shift just fine when I just barley hold the large shifter while shifting the small shifter.

retired358

Russ Ross: I did check and both brifters have the screw you mentioned in place...so still looking for a solution.

The problem must relate to whatever it is which keeps the large lever from moving when the small lever is pushed.

icemilkcoffee 

You just have to tear it down to see. Flushing the lever without tearing it down doesn't work all that well anyways.

KCT1986

The ST-7700 has a shifting mechanism that is different from most of the common brifters of the same era. It needs a certain amount of pressure holding the large lever in place for the small lever to work. This pressure is provided by the spring under the front cover and cable tension if I recall correctly. Had a problem with one of these and couldn't get it to work. Chalked it up to wear on the mechanism or weakened spring.
One fix that I've read about is drilling a new hole in the front cover for the spring to increase the spring tension.

If you haven't already seen this site, it's got some info and pics. Hope that the link works.

Stripping Shimano Dura-Ace 9-Speed STI Levers (norvil.net)

jccaclimber

I've resolved that issue in at least one 9sp STI lever of that vintage, but it's been nearly 15 years since I did so. You really do need to tear it down if flushing doesn't work. Be careful with the Flight Deck cable if you want that to work after. Take pictures as you go, particularly of the placement and orientation of all springs you come across. Be aware that getting some of the springs and parts back in can be a bit touchy. Doable, but requiring patience the first time or two. These are just several ratchet mechanisms all nestled together. Ratcheting one way is easy, like a socket wrench. Being able to ratchet one way but release a specific amount the other way is a bit trickier. Some of the internals rely on a spring controlling the order the pawls engage in. If one of these springs breaks, or the lubricant in one of the pivots becomes thick enough that they don't engage in the correct order then you get what you have. The other common symptom (more on the 6500 Ultegra shifters in my case) is that the large lever shift will occasionally rotate and miss the first or even second shift. Different symptom, but same general cause.

Since you've already tried flushing your options are to hope a stronger solvent works (not highly likely at this point), or take it apart, clean it, lubricate, and reassemble. If you happen to find a broken spring or worn down pawl you'll probably have your issue, but if not then getting everything clean and properly lubricated will probably fix the issue.
The times I've seen a worn down pawl I suspect it started as a pivot lubrication issue. The sticky pivot or chunk of sludge in the ratchet prevented the pawl from fully engaging, and then over time it wore down due to having to carry the same load with less engagement.

retired358

KCT1986 & jccaclimber: Thank you for your input. Looks as if I have a project in front of me.