TallRider

I'm wondering if 9-speed Campy rear derailers can be used with 8-speed Campy indexed systems, or does 9-speed have a different cable pull? I Googled for a bit and was surprised that I couldn't find this. (For comparison and to illustrate what I mean, Shimano 9-speed rear derailers can be used on a Shimano 8-speed drivetrain, excluding Dura-Ace which had a different cable-pull ratio for 7 and 8 speed, then went to normal Shimano starting with 9-speed).

A friend recently broke his Campy 8-speed rear derailer and needs to replace it. The tab which holds the b-screw (or whatever it's called in Campy world) snapped off, which is a weird failure. His chain was frozen and he was backpedaling trying to free it up. It's hard for me to imagine how that would snap the b-screw holder. My friend is strong but is decently mechanical.

But I'm mainly interested in whether a 9-speed Campy RD would work as replacement, or does he have to find an 8-speed. If my friend can use a 9-speed Campy RD, that opens his buying choices a bit.

TallRider

I'm surprised no one knows the answer to this, despite over 50 views of this post. I realize not that many people have come in contact with this issue, but it's a simple informational question:

"Will a 9-speed Campy rear derailer index properly with 8-speed Campy shifters and cassette?" Campy 8-speed, esp Ergopower, may not have been around for that long, either. But I figured someone here would know.

alcjphil

There were 2 generations of Campagnolo 9 speed derailleurs. The first generation had a B screw like the 8 speed versions and would probably work just fine. The second generation relied on a different method to adjust derailleur tension similar to 10 speed derailleurs. If you can find a 9 speed derailleur with a Shimano style B screw adjuster, it will probably work just fine

TallRider

Thanks for responding. Do you know if the later type, without a Shimano-style b-screw, required a different style derailer hanger, or had a different cable-pull ratio? (I doubt Campy shifted the Cable pull halfway through 9-speed, but the different adjustment mechanism replacing the b-screw could be an issue for pairing with 8-speed drivetrains).

MarcoBianchi

Maybe this would help.
Art's Cyclery Blog » Science Behind the Magic | Drivetrain Compatibility

alcjphil

Derailleur hangers do not change, rather derailleurs are designed to fit existing hangers. There was a slight change between the newer and older style Campagnolo 9 speed derailleurs in respect to pull ratio. Older shifters can work with the newer derailleurs , but maybe not perfectly. My brother broke his first generation Campagnolo Chorus 9 speed derailleur and asked me to repair it. I could not find a direct replacement, nor could I find the parts to upgrade his shifter to the newer pull ratio. However, the second generation 9 speed derailleur that I did find worked very well with his first generation 9 speed shifter, so all was well in the end

TallRider

Thanks, this helps. So Campy switched their cable-pull geometry of the rear derailer partway through the 9-speed era, as @alcjphil described. An older 9-speed (with the b-screw style design) or any 8-speed will work properly with an 8-speed Campy drivetrain.

fietsbob

Probably
"speeds" is not in the RD itself, it just moves inward with cable pulling it..
across the gear-cog cluster.

compare parallelogram pivot to pivot distance...
& inward motion, for a given cable pull amount..

TallRider

Exactly. This is why I am asking about cable-pull geometry. The link shared by MarcoBiancho covers these differences and gives precise measurements.

fietsbob

I'd just try it. I'm a mechanic, not a computer code writer .. posting from work.

IDK why this forum always wants others to do things for them...

SJX426 

@TallRider - I can understand the issue. I have been converting my 740x drive train to Campy. One of the challenges is that the 8V DA cassette has a different spacing than the Campagnolo equivalent. I found a Wheels Mfg spacer kit (discontinued) for the DA cassette to space the DA cassette block to match the Campagnolo spacing.

P1010339, on Flickr

Next was a 9V Campy RD using 8V ergo's. Works like a charm. My first experience with Ergos or "Brifters." I love riding that bike so much more with the ease of shifting now.

P1010333, on Flickr

P1010552, on Flickr

TallRider

To my mind, indexing compatibility is a basic thing on which it makes sense to first attempt to draw on existing knowledge base. As opposed to things that are fundamentally trial and error, such as what kind of saddle is most comfortable for a given person. In the case of this thread, there actually is a right answer.

I started this thread because I'm advising my friend on whether to buy a used 8-speed campy derailleur on eBay vs a new 9-speed, to replace a broken derailleur on his 8-speed drivetrain. Turns out the available new nine speeds are the new, slightly different cable pull ratio, which'll index fairly well but get worse toward the edges of the cassette. So, I got my answer while ago in this thread. Only needed one bump to start getting answers.