Dura Ace STI 10 speed shifter problem

Friend has Shimano Dura Ace STI 10 speed mechanical shifters on a bike. When shifting either shifter, to smaller cogs on the rear, and small ring on the front, the shifters do not work 1/3 to 2/3 of the time. In both of these scenarios the shifters release tension on the cable and allow the derailleur to move/swing to the smaller cog or chainring. But his shifters do not seem to cleanly release the tension on the cable and thus will not shift.

When shifting to bigger cogs on the cassette or up to the big chainring, both shifters work perfectly. In that scenario the shifter is pulling on the cable and it seems to have a good grip on the cable and pull the right amount. Not surprising since its always more dependable to pull on a flexible cable than to try to push on a flexible cable.

Anyone familiar with this scenario? Happened to you or others you know? Any specific part in the shifter to be replaced to cure it? Shoot it full of WD-40 or lubricant and shift it a bunch of times and hope that works for awhile?

A mechanic at a bike shop looked at the bike and said he was familiar with this scenario of not shifting right. Don't think he offered any way to fix it. Just buy a new shifter and if it happens with the new shifter, buy another new shifter, etc.

On 3/19/2020 4:23 PM, wrote:
Friend has Shimano Dura Ace STI 10 speed mechanical shifters on a bike. When shifting either shifter, to smaller cogs on the rear, and small ring on the front, the shifters do not work 1/3 to 2/3 of the time. In both of these scenarios the shifters release tension on the cable and allow the derailleur to move/swing to the smaller cog or chainring. But his shifters do not seem to cleanly release the tension on the cable and thus will not shift.

When shifting to bigger cogs on the cassette or up to the big chainring, both shifters work perfectly. In that scenario the shifter is pulling on the cable and it seems to have a good grip on the cable and pull the right amount. Not surprising since its always more dependable to pull on a flexible cable than to try to push on a flexible cable.

Anyone familiar with this scenario? Happened to you or others you know? Any specific part in the shifter to be replaced to cure it? Shoot it full of WD-40 or lubricant and shift it a bunch of times and hope that works for awhile?

A mechanic at a bike shop looked at the bike and said he was familiar with this scenario of not shifting right. Don't think he offered any way to fix it. Just buy a new shifter and if it happens with the new shifter, buy another new shifter, etc.


I'm not there, but what you describe is typical of gear
wire/casing troubles or in extreme cases crudded up gear
changer pivots (unlikely).

Shift it to small small.
By pressing on the rear changer body (not the shifter) see
if it returns well from a one-sprocket shift and a two
sprocket shift. Press, then let go. If it returns smartly
you likely have a gear wire problem. Ditto front same
technique.

Besides wire inside casing, smashed casing, kinked wire,
broken (especially plastic) ferrules, take a look at a BB
nylon guide if supplied. A drop of oil there is two seconds
but a billable miracle cure.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971

On 3/19/2020 6:02 PM, AMuzi wrote:
On 3/19/2020 4:23 PM, wrote:
Friend has Shimano Dura Ace STI 10 speed mechanical shifters on a
bike.Â* When shifting either shifter, to smaller cogs on the rear, and
small ring on the front, the shifters do not work 1/3 to 2/3 of the
time.Â* In both of these scenarios the shifters release tension on the
cable and allow the derailleur to move/swing to the smaller cog or
chainring.Â* But his shifters do not seem to cleanly release the
tension on the cable and thus will not shift.

When shifting to bigger cogs on the cassette or up to the big
chainring, both shifters work perfectly.Â* In that scenario the shifter
is pulling on the cable and it seems to have a good grip on the cable
and pull the right amount.Â* Not surprising since its always more
dependable to pull on a flexible cable than to try to push on a
flexible cable.

Anyone familiar with this scenario?Â* Happened to you or others you
know?Â* Any specific part in the shifter to be replaced to cure it?
Shoot it full of WD-40 or lubricant and shift it a bunch of times and
hope that works for awhile?

A mechanic at a bike shop looked at the bike and said he was familiar
with this scenario of not shifting right.Â* Don't think he offered any
way to fix it.Â* Just buy a new shifter and if it happens with the new
shifter, buy another new shifter, etc.


I'm not there, but what you describe is typical of gear wire/casing
troubles or in extreme cases crudded up gear changer pivots (unlikely).

Shift it to small small.
By pressing on the rear changer body (not the shifter) see if it returns
well from a one-sprocket shift and a two sprocket shift. Press, then let
go. If it returns smartly you likely have a gear wire problem.Â* Ditto
front same technique.

Besides wire inside casing, smashed casing, kinked wire, broken
(especially plastic) ferrules, take a look at a BB nylon guide if
supplied. A drop of oil there is two seconds but a billable miracle cure.

I don't have Andrew's experience, but cable problems are the first thing
that occurred to me, too.

How do the cables run on that bike? Internal or external? If external,
how clean and lubricated are the guides at the bottom bracket? And if
external, shift it on the workstand by pulling then releasing the free
span of cable running between head tube and bottom bracket. Watch what
happens, see what's sticking.


--
- Frank Krygowski

On Thursday, March 19, 2020 at 2:24:00 PM UTC-7, wrote:
Friend has Shimano Dura Ace STI 10 speed mechanical shifters on a bike. When shifting either shifter, to smaller cogs on the rear, and small ring on the front, the shifters do not work 1/3 to 2/3 of the time. In both of these scenarios the shifters release tension on the cable and allow the derailleur to move/swing to the smaller cog or chainring. But his shifters do not seem to cleanly release the tension on the cable and thus will not shift.

On Thursday, March 19, 2020 at 2:24:00 PM UTC-7, wrote:
Friend has Shimano Dura Ace STI 10 speed mechanical shifters on a bike. When shifting either shifter, to smaller cogs on the rear, and small ring on the front, the shifters do not work 1/3 to 2/3 of the time. In both of these scenarios the shifters release tension on the cable and allow the derailleur to move/swing to the smaller cog or chainring. But his shifters do not seem to cleanly release the tension on the cable and thus will not shift.

On Saturday, March 21, 2020 at 9:42:56 AM UTC-5, Tom Kunich wrote:
On Thursday, March 19, 2020 at 2:24:00 PM UTC-7, wrote:
Friend has Shimano Dura Ace STI 10 speed mechanical shifters on a bike. When shifting either shifter, to smaller cogs on the rear, and small ring on the front, the shifters do not work 1/3 to 2/3 of the time. In both of these scenarios the shifters release tension on the cable and allow the derailleur to move/swing to the smaller cog or chainring. But his shifters do not seem to cleanly release the tension on the cable and thus will not shift.

When shifting to bigger cogs on the cassette or up to the big chainring, both shifters work perfectly. In that scenario the shifter is pulling on the cable and it seems to have a good grip on the cable and pull the right amount. Not surprising since its always more dependable to pull on a flexible cable than to try to push on a flexible cable.

Anyone familiar with this scenario? Happened to you or others you know? Any specific part in the shifter to be replaced to cure it? Shoot it full of WD-40 or lubricant and shift it a bunch of times and hope that works for awhile?

A mechanic at a bike shop looked at the bike and said he was familiar with this scenario of not shifting right. Don't think he offered any way to fix it. Just buy a new shifter and if it happens with the new shifter, buy another new shifter, etc.

Have you resolved your problem?

I emailed my friend the responses given here. He had watched a YouTube video earlier talking about flooding the shifter with WD-40 and lubricant. A solution I had suggested too. He tried that and the shifter seems to be working. But he appreciated the responses given. And I will suggest again that he re-cable the bike and pay attention to cutting the housing cleanly. So right now the problem seems to be solved but I don't know for how long. Right now he is using this bike on an indoor trainer so maybe the fixing of the problem is not too critical. But I suspect even with a trainer, you want the bike to shift correctly.