Campagnolo RD Technical/Upgrade Questions

I'm thinking of making a couple of upgrades to my Tom Crowther, mainly because the freewheel is sticking and despite several attempts to free it up its not improved any. It also gives me an opportunity to replace it with a larger top sprocket.

Its currently set up with a 6 speed freewheel, the largest cog being 24T, 126mm rear spacing and a 1978 Nuovo Record RD.

I'm thinking of changing to a 7 speed freewheel with a 28T sprocket, I think the 7 speeds are only marginally wider but will it replace the 6 speed ok? As I understand it the Nuovo Record RD won't be able to cope with a 28T cog, so the second part of the plan is to use a 79/80 Super Record RD which I think will run a 28T sprocket.

Does this sound like a plan thats going to work?

78 NR will take the 28 sprocket just about . The problem comes when you use the inner chainring ring on the smaller sprockets as the chain starts to get a bit slack. Remember you will have lengthened the chain to cope with the big ring and the big rear sprocket.

Do you mind using one of the slant pantographs from the period? There's the option of also going thin chain\Winner from Suntour at usually a premium cost.

Shaun

Hi Shaun,

Thanks, I'd not thought about a slack chain I really want to stick with Campagnolo as everything else is Campag. I could just do with it being a bit easier up the hills!

I would not go with 7 speed as it really needs slightly wider rear drop outs. Stick with 6 speed and use a 28T cog and you Nuova Record should be fine. As Midlife says you have to watch chain slack so calculate how many tooth difference you have at both front and back, e.g. 14 -28T rear and 52 - 42T front = 24T difference which the Nuova Record can cope with but you may find on the larger chain ring you cannot get all the rear gears and you have to forgo the 28T and just use it on the smaller inside chain ring. As you only want it for hill climbing that will be ok.
For what it's worth I used a Nuovo Record on a 1960s Andre Bertin 5 speed with a 28T large cog and a total difference of 26T and had to lose the two larger cogs when using the big chain ring. I rode it at L'Eroica Britannia this year and despite frequent gear changing on those hills it never faulted so long as I worked within its abilities. I find with the older rear derailleurs you have to work within their limits and don't overstretch them.

Re:

I ran Campag 9 spd on a 126mm Colnago Master frame without issue. So long as you use a small top sprocket, you should be fine.