Bike only shifting accurately when chain on small ring
08-03-18, 11:03 AM
#1
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Bike only shifting accurately when chain on small ring
having an odd problem. Im runnin an 8 speed shimano 600 indexed system. The bike seems properly indexed- it hits all rear cogs smoothly when in the small chainring. Things start to get funky and inaccurate when i shift to the large ring. When in the large ring the indexing is off. It wont shift smoothly to the second cog and not at all to the third. It hits the rest fine (obviously i prob wouldnt shift much lower when in the big chain ring). I check the hanger alignment and it is just fine. Any ideas!?
08-03-18, 06:47 PM
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Chain length? How big a tooth difference between the rings? AS the chain needs more play out (when on the big ring) the der cage rotates and the guide pulley drops away from the cog undersides. This creates larger cog to pulley gaps and more chain links that need to travel through their lateral slop before the next link will move. get enough lateral play (or links with a bit each) and the chain will only flex and not ride up and off it's current cog. Andy
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AndrewRStewart
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08-04-18, 05:45 AM
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Did you recently change the rear cassette/freewheel for a different one? Perhaps to get better gearing for where you ride? Since you're running 8sp (which has been around for a while), I see two possibilities.
First - the chain is worn, and flexes more than the rear derailleur wants/needs. If this is the case overshifting should still result in a shift to the next larger cog.
Second - the rear cassette/freewheel is either worn (or at least the smaller cogs are worn), or is new and the chain was not replaced along with the cassette/freewheel. Normally, if you're replacing a worn cassette/freewheel, you would replace the chain as well as they tend to wear together. The chainrings don't usually wear at the same rate as the rear cogs.
First - the chain is worn, and flexes more than the rear derailleur wants/needs. If this is the case overshifting should still result in a shift to the next larger cog.
Second - the rear cassette/freewheel is either worn (or at least the smaller cogs are worn), or is new and the chain was not replaced along with the cassette/freewheel. Normally, if you're replacing a worn cassette/freewheel, you would replace the chain as well as they tend to wear together. The chainrings don't usually wear at the same rate as the rear cogs.
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Dale, NL4T
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08-07-18, 06:17 PM
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One thing you might try is to check the B-Screw adjustment.
Adjust so that the upper guide pulley on the derailleur is as close as possible to the cassette in all gear combinations without actually rubbing.
Adjust so that the upper guide pulley on the derailleur is as close as possible to the cassette in all gear combinations without actually rubbing.
08-07-18, 07:02 PM
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Spring tension in the der weak? Gummed up?
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08-07-18, 11:25 PM
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Another idea to check/eliminate - could be a bent rear derailleur hanger. The more chain tension, the worse the problem becomes.
In the large chainring, if you pedal backwards does the chain skip on the cassette? If it does, I would have a look at the rd alignment.
In the large chainring, if you pedal backwards does the chain skip on the cassette? If it does, I would have a look at the rd alignment.
08-08-18, 09:18 AM
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Is it safe to say that this is a new development? Was the shifting fine for years and this just started? If so, you haven't made any changes that caused this?
John
John
