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Old 01-27-23, 01:04 PM
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Unca_Sam
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Join Date: Oct 2018
Location: Columbus, OH
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Bikes: Pake C'Mute Touring/Commuter Build, 1989 Kona Cinder Cone, 1995 Trek 5200, 1973 Raleigh Super Course FG, 1960/61 Montgomery Ward Hawthorne "thrift" 3 speed, by Hercules (sold) : 1966 Schwinn Deluxe Racer (sold)

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Originally Posted by austinbikebill
Hi all.

First, a thank you to everyone on this forum who weighed in on my shifter upgrade from downtube shifters. After considering an upgrade to index shifters, I ended up staying "analog" and going with some dia compe bar end shifters instead. Very happy with them.

On to my current problem.

I have a drivetrain that is effectively a 9 speed at the moment. If I try to go to the large chainring - largest sprocket combination, the chain comes up short, maxing out the derailleur and locking up the chain so tight that I have to take the wheel off to release the tension and reset the drivetrain.

I think I still have the original chain on the bike, so I bought first a 7.3mm 1/2" x 3/32" 116 link chain designated for 5-8 speeds and installed it.

At the 116 link length, the new chain would let me get on to the large chainring - largest sprocket combination, but the chain would then skip-jump when on the two smallest sprockets,

I took out first 2 links (to 114 net links), then 4 links (to 112 links) and the same behavior worked on larger three sprockets, skipped on the smallest two sprockets. Oddly, at 112 links, it would still go onto the large chainring - largest sprocket combination.

I then bought a beefier 7.8mm 116 link chain designated for 5-6 speed use, and I got the same results: skipping-jumping on the lower 2 sprockets, good on the three largest sprockets.

I (think I correctly) measured the legacy chain the with a caliper and came up with 7.96-8.0mm width (at the pin: I got 7.28-7.30 at the pin on the first chain and 7-76-7.80 on the second chain).

I no longer have the original Suntour "Blue" series derailleur, having replaced it with another Suntour derailleur with the same jockey arm (?) length.

So what do you folks think?

Is my drivetrain so old that I need an even beefier single speed chain?

Is my derailleur just tired (it probably has over 10,000 miles on it since installed) and not maintaining sufficient tension in the chain when at its most slack on the smaller sprockets.

I would really like to get over the hump on this 9 speed issue and have my Nishiki fully functioning again, so any insights/ideas would be most appreciated.
I think your freewheel has seen the end of its useful life if it's skipping with a new chain. You should make note of the tooth count you have on the freewheel cogs and look for a replacement to go with your new chain. Chainrings wear a little slower but that wear is accelerated by a chain that is more out of spec than 1/2% (slightly more than 1/8" over 3 feet). If you pull the new chain as installed from the front of the chainring, can you pull it away from the chainring by more than a tiny bit?

There are lots of ways to size a new chain for your drivetrain, but the simplest is to put the chain over your largest chainring and cog, determine the length, and then add an inch. Tired derailleurs can lose your chosen gear on rough roads, but they wouldn't be the source of skipping.

Last edited by Unca_Sam; 01-27-23 at 01:11 PM.
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