Phantom shifting under load
Went on xmas day ride and suffered from the phantom shift issue. It is sn old bike dura ace I never used before, 9 speed shifts feel different than my 105 10 speed. So why is it shifting under pressure and what’s the fix thanks |
Originally Posted by thehammerdog
(Post 20720387)
Went on xmas day ride and suffered from the phantom shift issue. It is sn old bike dura ace I never used before, 9 speed shifts feel different than my 105 10 speed. So why is it shifting under pressure and what’s the fix thanks If if they are integrated shift levers I would be curious the mileage on them. Lately here I have encountered quite a few 9 speed STI brifters that just slip completely and flushing them out doesn’t help either. Apparently some of these failing high mileage shifters are toast and need replacement. |
What's the frame? Some older frames were laterally flexible enough that the rear triangle would move sideways under chain tension enough to cause a shift. Closely spaced cogs like 9 or 10 speed made this more of a problem.
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Originally Posted by masi61
(Post 20720396)
If these are down tube shift levers the obvious question I would as is: is the screw holding it onto the braze on boss tight enough? |
First thing I ask is if the chain is really moving to another cog/ring and if so which. If not then worn chain/tooth skip is the likely issue. If moving to another cog then I'd look at the cable first. If the cable's movement is hanging up for some reason (internal to housing friction, kinking, fraying strands in shifter....) If the cable is hanging up and not fully moving then the added forces (that flex the frame) can cause the hang up can let go and the der can move. Other reasons can cause this too but that's where I would start. Andy
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My observation (sight unseen)
All the engineering to make a faster shifting cassette has that side effect, if everything is not in adjustment, and derailleur hanger alignment is part of that...
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My bike began to have poor shifting at one point after about 15,000 miles. No amount of messing with it cured the problem. One day while scratching my head and playing with components. I discovered the rear derailer had considerable lateral play, presumably due to eccessive wear. A new derailer, an easy fix, cured the problem.
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I guess frame flex. It was common back in the days of steel. That is , if the frame is steel
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Originally Posted by MarcusT
(Post 20721452)
I guess frame flex. It was common back in the days of steel. That is , if the frame is steel
Start at the beginning. Has the bike been siiting idle for a while. If so and it was correctly adjusted first it didn't go out of adjustment while it sat there. Pinch bolts don't loosen cables don't fray etc. Wd40 all cables shifter and derailleurs make sure.they move freely. Then look for adjustment issues. Then chain and cassette. While your at it look at the brakes. Dura ace equipped bike ghost shifting because of frame flex, really. |
Originally Posted by blamester
(Post 20721629)
Why guess.
Dura ace equipped bike ghost shifting because of frame flex, really. |
chain s new but drive train is not 2001 cables were gross gunked up I replaced and tighten up stuff felt good on stand but need to ride it it may be an old cassette I hope not because they aint cheap
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Originally Posted by MarcusT
(Post 20721649)
Yes, this urban myth and others existed waaaay back in the 20th century. Another is; bikes only had one mount for a water bottle. You had to actually remove your hands from the handlebars to change gears and then adjust the derailleur until it was in the right position. Don't even get me started about the box wrenches you needed just to adjust a seat. :50:
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I have a Giant NRS MTB that suffered from "ghost shifting" under load since new. Apparently it was a somewhat common problem as I found a few others who had the same issue with the same bike and the theory was that it was flexing in the rear triangle. In any event, the cure was to run cable housing from the last main triangle cable stop all the way down to the RD. Problem solved.
- Mark |
Yeah, I had a lot of ghost shifting with my '89 Centurion Ironman when I tried using the Suntour GPX Accushift stuff in friction mode. It was a combination of problems:
The only way to fix the problem was to get the Accushift index mode working satisfactorily, or replace the downtube shifters with something that would hold without excessive tension. |
Originally Posted by thehammerdog
(Post 20720387)
Went on xmas day ride and suffered from the phantom shift issue. It is sn old bike dura ace I never used before, 9 speed shifts feel different than my 105 10 speed. So why is it shifting under pressure and what’s the fix thanks |
My ghost shifting is definitely frame flex. It doesn't bother me because it always downshifts just when I need it like an automatic transmission, :giver:
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Originally Posted by HillRider
(Post 20720417)
What's the frame? Some older frames were laterally flexible enough that the rear triangle would move sideways under chain tension enough to cause a shift. Closely spaced cogs like 9 or 10 speed made this more of a problem.
I can verify this from experience. I have an old Bridgestone Radac (basically a Japanese Vitus, bonded aluminum). 8sp worked fine on it but I get ghost shifts with 9sp. |
I have a lot of ghost shifting. I have about 60,000 miles on these Campy 9 speed record shifters.
My question, most likely the play in the worn shifters? Bike not dumped but maybe housing, cables etc |
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