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Discussion Starter · #1 ·
I recently bought a new freewheel--yes freewheel--for my old chesini--

From the rubbing and grinding, I surmise that the 28 tooth cog exceeds the maximum for my, admittedly very old, Dura Ace 7400 derailleur. I've played with the adjustment screw, and even at it's max I'm not getting enough clearance between the cog and the pulley.

I wonder if there are any alternative adjustments (longer screw perhaps, or a shim) that will make it possible to run this combo, or if it will never work.

Any thoughts?
 

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Just guessing here because I'm not sure what you mean by "range" and what's rubbing or grinding on what. But if the chain-loaded upper derailleur pulley jams against the bottom of the 28 cog, try shortening your chain. You can simulate this first by pulling on the lower chain run and watch what the upper pulley does.

Note: your chain might already be as short as possible. The chain needs to be long enough so you can ride in the big front-big rear combination, even if don't think you ever will. If you shorten the chain too much, the big-big combo will break stuff shortly after the fateful shift.
 

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Discussion Starter · #3 ·
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Basically, the problem is that the max rear cog for a dura ace is something like a 26, and the 28 is in contact with the top pulley.

The adjustment I'm talking about is the screw that changes the angle of the rear derailleur in relation to the frame. it contacts the top of the derailleur hanger, and, in effect, changes the distance distance between the freewheel cogs and the upper pulley. I think Sheldon Brown calls it the B pivot or something like that.

The chain is actually too short now, so I don't think that can be the problem. I switched over from a 24tooth large cog to the 28. adding tension to the chain doesn't help, but rotating the derailleur body (like you would to change the rear wheel) even slightly gives enough clearance, which is what makes me wonder if a shim or longer screw would solve my problem..
 

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I've run 27 tooth with no problems..Since you have the b set screw adjusted all the way, you might be out of luck. Your problems are further complicated with a 7400 DA derailleur.
They have a unique geometry for indexing so changing rear derailluers will also require changing shifters.

You can either switch your freewheel to 27T or smaller or change rear derailleur/shifters.
 

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Clear enough now.

I've heard of replacing the B-tension screw with a longer one to gain some clearance, but it's been too long ago for me to remember the outcome. Some derailleurs also had an internal spring tension adjustment, which involved some disassembly, then moving the spring wire prong into a different cut-out or hole.

Check and see if the rear axle is as far back in the dropout as it will go.
 
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