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Campy Potenza RD Tension Spring...

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Campy Potenza RD Tension Spring...

Old 09-14-19, 12:01 PM
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jad3675
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Campy Potenza RD Tension Spring...

On the last leg of a ride this AM, after downshifting to 1st on the smallest front ring something felt a little off. Could not really stop since I was climbing and I was about a half mile from home. When I got home and off the bike the chain was really loose. It appeared that the RD was not taking up the slack from being in small ring and large cog. Removed the RD - and yeah, the b tension adjustment plate was easily turnable by hand and not at all tensioned. Took it apart and it appears that the tang on the derailleur side (not the plate side) had escaped the notch in the derailleur. There was no obvious damage to the spring or either notch on the unit. Cleaned everything up and put it back together. So fair it appears to be working. Of course, I have a 65 mile charity ride tomorrow...sigh. Guess we'll see how that goes.

This drivetrain is barely a month old - has maybe 600 miles on it. This is the second issue I've had with it - the other one was a broken paddle shifter on the left hand brifter.

I realize the commonality here is the idiot holding the wrenches - I've never seen or had this issue on other bikes (none of which were Campy, though).

Has anyone else had this issue? What could cause the tension spring to slip its notch? Too much cable tension on the RD? Too much Limoncello at the Campy factory when they put the unit together?

BTW, Chain was cut to length using the Campy way using the Park Tools video - https://www.parktool.com/blog/repair...ing-campagnolo

John
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Old 09-14-19, 01:06 PM
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Dave Mayer
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I've successfully serviced dozens of rear derailleurs - down to the springs. I rebuilt a couple of wonky Campagnolo 10-speed era units this month.

Most likely the need for rebuilding is due to (minor) crash damage, or dummies who degrease their derailleurs whole in a solvent bath. Or use a pressure washer to clean their bikes.

I have never seen one of the two internal derailleur springs jump out of its hole, except under significant duress. Of course you sized your chain correctly right?...

The chain should have the ability to wrap around the biggest cogs front and rear. So the big-big combo, plus an extra inch of chain...
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Old 09-14-19, 02:44 PM
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Originally Posted by Dave Mayer
I've successfully serviced dozens of rear derailleurs - down to the springs. I rebuilt a couple of wonky Campagnolo 10-speed era units this month.

Most likely the need for rebuilding is due to (minor) crash damage, or dummies who degrease their derailleurs whole in a solvent bath. Or use a pressure washer to clean their bikes.

I have never seen one of the two internal derailleur springs jump out of its hole, except under significant duress. Of course you sized your chain correctly right?...

The chain should have the ability to wrap around the biggest cogs front and rear. So the big-big combo, plus an extra inch of chain...
Yeah, chain is sized the campy way - small chain/small ring, 8mm between the horizontal chain run and the chain around the top jockey wheel, like this:
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Old 09-14-19, 03:05 PM
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This chain measuring approach ensures that the chain is not too long. It does not ensure that the chain is too short, a far more critical criterion.

So on the stand, shift into your big ring. Then carefully ratchet up the cassette to ensure you have at least an extra inch of chain when running in the big-big combo.

Yes, I know that big-big is not a gear combo that we're supposed to be riding in. But regardless the level of rider experience, we all will find our way into this combo - eventually.

No reason to damage or tear off a derailleur because of a too short chain. I've done it.
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Old 09-14-19, 03:20 PM
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The little/little method insures that the chain is as long as possible. The only way that it would not wrap the big/big is if the OP is using some gear combination that is not recommended by Campy. The big /big method may suggest a shorter chain, unless you're using the largest recommended big sprocket.

Last edited by DaveSSS; 09-15-19 at 01:29 PM.
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Old 09-14-19, 04:48 PM
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Originally Posted by DaveSSS
The little/little method insures that the chain is as long as possible. The only way that it would not wrap the big/big is if the OP is not using some gear combination that is not recommended by Campy. The big /big method may suggest a shorter chain, unless you're using the largest recommended big sprocket.
Yeah, the chain has plenty of length with the small/small sizing. Rear cassette is Shimano 11/28 so it's one tooth smaller on the big than the equivalent campy size.

Even at big/big, the RD has a good amount of extension left in it - I don't think it's a matter of big/big overextending the RD. When the issue happened I was already on the smaller ring, too...

John
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Old 09-15-19, 09:47 AM
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Well, had zero issues on a 65 miles charity ride through the hills of Kentucky this morning. Maybe it was assembly error at the factory?

John
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