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Old 12-26-12, 12:25 PM   #1
d.wayne
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Chain Line on 9 Speed Campagnolo Drive Train with 7/8 Speed Cranks

Hi,

Merry Christmas everyone!

I've been retooling my drive train on my vintage road bike. After my upgrades, my rear derailleur makes a clicking noise on the largest two cogs (23 and 26). I've checked the pulleys for wear, the derailleur hanger alignment, and the b-stop screw adjustment. Everything looks good so I was wondering if my chain line could be a problem. My shifting is crisp and works well other than the clicking on the largest rear cogs - it clicks at various degrees using either my 39 or 53 front chain ring.

Here is my setup:
- Campagnolo Chorus Crank (1988) originally for 7 and 8 speed Index Shifting with 39/53 chains
- Campagnolo Chorus Bottom Bracket (1988) - Italian Tread 70/110 spindle
- Campagnolo Chorus 9 speed rear derailleur and brifters (1997)
- Campagnolo Chorus 9 speed cassette 13-26 (this is New Old Stock)
- New KMC 9 Speed Chain shortened using Campagnolo's longest length method

So my main question is that from looking at the literature, the older Campagnolo 7/8 speed setups had a 45mm chain line with a 110mm bb spindle length. It appears that all of the newer 9 speed and up chain lines are 43.5 - with a 102mm bb spindle length. Can this difference (i.e. the 45mm on my 8 speed vs the 43.5 on 9 speed cranks) cause the clicking issue? I am thinking about getting a Phil Wood or Campagnolo CART bottom bracket that would allow me to adjust my chain line but I wanted to get some feedback first.

Thanks, Duane

Last edited by d.wayne; 12-26-12 at 03:06 PM.
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Old 12-26-12, 01:19 PM   #2
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I doubt chainline is the issue, because it comes into play more at the tight upper loop than at the bottom.

If you're sure it's the derailleur, the problem could be a bent hanger, which pushes the lower pulley inboard of the sprocket increasing the lower loop chain angle with the inner sprockets. The increased angle causes the chain to climb off the lower pulley then settle in causing the clicking. A worn lower pulley can cause the same problem even if the RD is straight.

In case you want to check chainline anyway,

Ideal chainline is when the center of the chainrings (between the rings on a double) lines up with the center of the cassette. That's when the chain runs closest to straight the most often. There's some give here, and I chose to have my cranks outboard od center a bit since I spend the most time on the outer ring with the outer half of the cassette. You can measure this for yourself as follows.

measure from center of the space between the rings to the down tube, and add 1/2 the tubes diameter.
measure from inside the dropout to the middle of the cassette, and subtract from 1/2 the axle width.
The number should match within 3-4mm either way.

A road double chainline is typically 43-45mm, but this can vary with different combinations of cassette and axle width.
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Old 12-26-12, 01:24 PM   #3
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Generally chainline on derailleur bikes, center of the rear cog cluster, and the center of the crankset.

.. in a double that is between the 2 chainrings, on a Triple, it is the middle chainring.
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