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Twist Grip to Thumb Shift on a Townie

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Twist Grip to Thumb Shift on a Townie

Old 10-03-20, 06:30 AM
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CNRed
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Twist Grip to Thumb Shift on a Townie

I have a rather old and previously abused Townie. From what I can tell the bike was produced in 2007 or 2008. I picked the bike up because I like the old frame with the intergrated frame bosses at the fork tube and the seat post.
The twist shifter on the bike was quite old and weathered so I thought I would replace it with a Shimano 7 speed thumb shifter. I got a new shifting cable and housing, I feel I have the rear derailleur tuned as the bike shifts well going up the rear cogs from 7th gear to the top 34 tooth cog. The issue is, it does not seem to want to shift from the top cog back down the cassette to the smallest cog with any consistency.
As I mensioned, the bike has lacked TLC in the past.
I'm wondering if I might have to change out the rear derailleur for a new one.
Has anyone made this modification before, and what if anything am I missing..
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Old 10-03-20, 07:05 AM
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dsbrantjr
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Did you just change out the inner shifting cable? If so there may be excess friction in the old housing, especially the loop going to the rear derailleur which tends to collect dirt and water. You can check your derailleur spring by shifting to the small cog then disconnecting the shift cable or pulling the housing out of a stop to allow slack and then pushing the derailleur in by hand while pedaling (watch your fingers!) and see if it returns to the smaller cogs readily. If it fails to shift only to the smallest cog perhaps the high limit adjustment is a bit too tight
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Old 10-03-20, 07:32 AM
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Shifting to larger cogs is increasing tension; to lower cogs is releasing tension. So something is likely binding. I had similar issues, solved by a drop of lubricant in each end cap. As mentioned in the post above, make sure the cable run is smooth. Then I would suggest checking rear derailleur drop alignment. Next youtube a video on indexing the rear derailleur (unless by thumb shift you mean un-indexed friction shifter).

If cable is smooth, and you're using friction shifting (and all drive train/shifting components are compatible), then you're down to possible chain/worn cog/derailleur issues.

If I've mispoken anything, the more mechanically inclined will set us straight.
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Old 10-03-20, 09:19 AM
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Originally Posted by Digger Goreman View Post
Shifting to larger cogs is increasing tension; to lower cogs is releasing tension. .
Usually true but not universally so. A bike from this era and type may have the Shimano Nexave group which were mostly if not all equipped with low normal rear derailleurs.
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Old 10-03-20, 10:12 AM
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dsbrantjr,
I changed the rear shifting cable and cable housing from the front of the bike to the rear to include the derailleur loop, the cable is running freely through the housing. I will disconnect the cable and test it as you described.

Digger Goreman,
I checked the
derailleur hang visually, I dont have the specific tool to check it, but it looks straight. I'm using an indexed Shamino 7 speed thunmb and trigger shifter though the Derailleur does not indicate what brand it is, I'm pretty sure it is a Shamino. I also used Park tools video for derailleur adjustment as I have in the past to adjust it, (Ive had good luck with this adjustment in the past with other bikes)

I believe the Derailleur is weak as suggested.
If it tests poorly I'm thinking a Shamino TX35 would be a replacement.
Any comments as to what to buy if it is bad?
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Old 10-03-20, 11:10 AM
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dsbrantjr
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Originally Posted by CNRed View Post
dsbrantjr,
I changed the rear shifting cable and cable housing from the front of the bike to the rear to include the derailleur loop, the cable is running freely through the housing. I will disconnect the cable and test it as you described.

Digger Goreman,
I checked the
derailleur hang visually, I dont have the specific tool to check it, but it looks straight. I'm using an indexed Shamino 7 speed thunmb and trigger shifter though the Derailleur does not indicate what brand it is, I'm pretty sure it is a Shamino. I also used Park tools video for derailleur adjustment as I have in the past to adjust it, (Ive had good luck with this adjustment in the past with other bikes)

I believe the Derailleur is weak as suggested.
If it tests poorly I'm thinking a Shamino TX35 would be a replacement.
Any comments as to what to buy if it is bad?
I have had good luck with Microshift as well as Shimano. You can use any Shimano-compatible rear derailleur from 6 to 9 speeds.
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Old 10-03-20, 11:26 AM
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Originally Posted by dsbrantjr View Post
I have had good luck with Microshift as well as Shimano. You can use any Shimano-compatible rear derailleur from 6 to 9 speeds.
Thank you, sir, gonna check the derailleur later today.
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Old 10-03-20, 03:57 PM
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I'm having a good multi-year run with a basic Shimano Altus (9 spd) rear derailleur
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