Hello Hope everyone is doing well.Need some help not Sure if I need to go to mechanic section or just stay in classic,Aways,1980 Faggin replaced 5sp freewheel 13t-26t to a 5sp 14t-28t rear derailleur is Campagnolo N/R.Won”t shift to 28t gear I changed gearing for Eroica.Thank you for your time and help.Be Save Peddle On

OK- the late Super Record rear mechs, shifted to the 28 better.
Check Velobase.com for visual reference.
That out of the way, back out the adjusters, you probably have the short dropouts as its a 1980, I would consider removing the adjuster screws and springs temporarily and slide the wheel aft, essentially all the way.
It will help, but if not enough... then alternatives are:

Shorten the chain the minimum amount ( with a gloved hand) twist a link to simulate a shorter chain along the return run of chain between the chainring and the jockey cage.
Watch the cage rotate away from the cog. The test prior is to go to the big/big combo, interestingly I have a bike that to get into the 28 (as I do not intend to keep that and plan going to a bigger big ring)... Must be in the big ring to accept the 28T.
I do not advise setting up the bike so it gets in trouble in the big/big even though you would not use that, duplication and friction.

So, try that and report back.
If not we will go to phase II.

You might have exceeded the maximum cog size for that derailleur.

Only if it a very early Super Record, and then we can get there. Pre Pat72, a problem.

I believe OP is using a NR derailleur. Will the NR derailleur work?

I have made NR derailleurs work on 28T rear clusters on numerous bikes. The trick is playing with the chain length and position of the wheel in the dropouts to ensure that the cage is rotated far enough forward so that the upper pulley of the derailleur is far enough below the 28T cog when in the next lowest gear. Chain length is absolutely critical to making this work. If you could post us a picture of the derailleur with the chain in this position we might be able to help.

+1 on chain length if you change gearing by several cogs you should change length buy 1 link per 1.5 cogs less or more on older Campy stuff. In This case I would recommend you change to a long cage Suntour DR and a new 114 link chain and all will be good
,

I have three NR derailleurs working with 28t cogs. Patent 72, 74 and 80. As mentioned, it takes chain length fiddling and dropout position fiddling. Also, big front-big rear is strongly advised against on all three of mine. Shifting is actually pretty good with new 6/7/8 speed chains and good freewheels, with the Shimano Z012 14-28 it is particulary good. In setting up one of them, it seemed that the derailleur cage had a strong desire to introduce itself to the spokes (stand testing only). So I gave in and put a spoke guard on it and very carefully adjusted the derailleur stop. Seemed to be the worst when there was enough chain to handle the big-big cross chaining.

+1 on checking chain length.Sometimes that's enough. Otherwise, position the wheel as far back in the dropouts as possible. You may need to remove the adjuster bolts (if any) to get the wheel far enough back. I've seen Nuovo Record derailleurs work with a 30T sprocket with the chain length right and the wheel far enough back.

There was a design change, the Pat 74 have just a bit more distance between the mount pivot and they upper parallogram links.
As mentioned, it can be done, just takes .... finesse.

The late Super Record had a different cage, a few I know have hot rodded their early Nuovo Record with the late cage to good effect.

I have done this without much trouble on various Eroica bikes. It is perhaps worth noting that all had 49T or 50T big rings.

I've had luck with a 28T cog on my Cinelli, by doing just what John said. I did have to remove the dropout adjusters. It didn't work with my Bianchi, frame geometry is different.

Kurt

That makes things Far easier.

In various ways.

As mentioned by non-fixie and repechage, having a narrower front chainring spread like 49/42 allows one to use a wider-range freewheel using the NR rear derailer.

I prepared a 1961 Raphael Geminiani for a guy who did Eroica using a 14-32T 6s freewheel using a NR rear derailer.

I got it to work through the whole range by adjusting chain length and axle position in the dropouts.

Tightening the chain was the key to clearing the biggest cog.

The narrower spread of chainring size definitely made this possible based on what I've learned from my previous struggles using the NR rear mech.

Always ensure that shifting to the big-big won't result in the chain "sticking" on the big-cog position, and that the chain doesn't go over-tight where there is sudden resistance felt at the pedals. Testing and adjusting in the bike stand is really useful here, even as I normally don't use a stand at all when building or working on bikes.

A slight bit of rumble felt in the small ring and biggest rear cog won't hurt anything when used only occasionally as expected on the hardest climbs.

I similarly use a 12-34t 9s cassette and 52/42t chainrings with an Ultegra 6503 Triple rear derailer rated for a maximum of 27t. I get just a hint of rumble as the top pulley just touches the largest cog when in the small chainring. It's a great setup that gives no problems over years of use! Shown below:

I have had this work well, but it can depend on geometry factors, such as chainstay length. Correct chainline matching front to rear can also have an effect, in my experience. It also depends on whether you meed equivalently clean operation in all gears. I'm terrible at avoiding cross-chaining, so I am rather picky.

As well, Campy and other companies have (but don't always publicize well) that there are two limitations: The maximum spread adds the range of the chainrings to the range of the sprockets, and there is a maximum value for that. There is also a limitation on the maximum rear sprocket size that the derailleur cage can clear when twisted over as much as it can be. Extending the length of the dropout tang helps, as is used on 1x12 systems.