The Campagnolo rear derailleur "H" screw...
I'm not talking about "H" as in High, i.e. one of the limiter screws, rather the screw underneath the attachment of the jockey cage that (according to the manual) you are supposed to adjust so that the top jockey wheel and the largest sprocket are 7mm apart.
I've always been a bit confused by this screw. For a start, it's incredibly difficult to measure the 7mm as you need to have the chain attached and the links largely obscure the teeth of the jockey wheel and sprockets at their closest points.. Also, if you wiggle the derailleur the measurement is different from what it would be if you had just changed to that sprocket. Also, does it need to be reset when you change cassettes, e.g. from an 11-23 to 12-27?
I generally seem to get snappier and more reliable shifting with this screw turned nearly all of the way in, so that the jockey wheel is closer to the sprockets. Any tips for measuring the 7mm?
I've always been a bit confused by this screw. For a start, it's incredibly difficult to measure the 7mm as you need to have the chain attached and the links largely obscure the teeth of the jockey wheel and sprockets at their closest points.. Also, if you wiggle the derailleur the measurement is different from what it would be if you had just changed to that sprocket. Also, does it need to be reset when you change cassettes, e.g. from an 11-23 to 12-27?
I generally seem to get snappier and more reliable shifting with this screw turned nearly all of the way in, so that the jockey wheel is closer to the sprockets. Any tips for measuring the 7mm?
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Adjust it so that the shifting is smooth, it needs to be fairly close, but it's not neccessarily 7mm.0
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got to admit, I'm baffled by this screw - it doesn't appear to do jack sh|t! I'd love to be able to fine tune my shifts with itneeb wrote:I'm not talking about "H" as in High, i.e. one of the limiter screws, rather the screw underneath the attachment of the jockey cage that (according to the manual) you are supposed to adjust so that the top jockey wheel and the largest sprocket are 7mm apart.
I've always been a bit confused by this screw. For a start, it's incredibly difficult to measure the 7mm as you need to have the chain attached and the links largely obscure the teeth of the jockey wheel and sprockets at their closest points.. Also, if you wiggle the derailleur the measurement is different from what it would be if you had just changed to that sprocket. Also, does it need to be reset when you change cassettes, e.g. from an 11-23 to 12-27?
I generally seem to get snappier and more reliable shifting with this screw turned nearly all of the way in, so that the jockey wheel is closer to the sprockets. Any tips for measuring the 7mm?
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The shifting is definitely different with it screwed in a lot and screwed out. It seems that If it is too far out, the shifting can be sluggish or impossible to adjust so that it works reliably in both directions, while if it is all the way in the shifting has a very hard, springy feel. The latter is definitely better, but having just screwed mine nearly all of the way in I think it's a bit much now and I'm going to back it off a bit until the shifting is smoothest, as per StephanP's advice. As it happens I think that will indeed be around 7mm, although how campagnolo expect you to measure this accurately is beyond me.0
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The screw is called the "B" screw and is not exclusive to Campag. It's used to adjust the angle of the RD and is set so that the distance between the upper pulley and the largest sprocket is minimal in order to achieve smooth changes. It's best to lift the RD up before adjusting as if left in position bearing down on the drop-out, it has a nasty habit of distorting. I tend to swap mine for an Allen-headed bolt making it easier to adjust.0
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Thanks - could you elaborate on this? Do you mean that you can bend the dropout by tightening the screw too much if you haven't lifted the derailleur first? By lifting, do you just mean pulling it away from the sprockets?onbike 1939 wrote:It's best to lift the RD up before adjusting as if left in position bearing down on the drop-out, it has a nasty habit of distorting.0 -
neeb wrote:
Thanks - could you elaborate on this? Do you mean that you can bend the dropout by tightening the screw too much if you haven't lifted the derailleur first? By lifting, do you just mean pulling it away from the sprockets?onbike 1939 wrote:It's best to lift the RD up before adjusting as if left in position bearing down on the drop-out, it has a nasty habit of distorting.
No, the screw itself is a bit flimsy and in use it screws down against the pressure of the return spring of the RD. So as to prevent the screw distorting as you're screwing it down as it bears on the drop-out, it's best to lift the RD, adjust the screw, release the RD and let the screw once again bear down on the small platform provided by the drop-out.
Easier to demonstrate then to describe I'm afraid.0 -
I've just fitted a veloce/centaur mix drivetrain to my Caad8 and this is one job I forgot to do :oops: I think I've just got into the habit of not messing with the B screw as, on Shimano stuff, it does bugger all (as rowlers said).
Just checked, and the upper jockey is about 5-6mm from the biggest cog. Changes are definitely on the firm/snappy side (which is good imo).0 -
Thanks, got what you mean now!onbike 1939 wrote:
No, the screw itself is a bit flimsy and in use it screws down against the pressure of the return spring of the RD. So as to prevent the screw distorting as you're screwing it down as it bears on the drop-out, it's best to lift the RD, adjust the screw, release the RD and let the screw once again bear down on the small platform provided by the drop-out.
Easier to demonstrate then to describe I'm afraid.
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Actually I find that the shimano one does do something, its just the campy that is odd :?Jon_1976 wrote:I've just fitted a veloce/centaur mix drivetrain to my Caad8 and this is one job I forgot to do :oops: I think I've just got into the habit of not messing with the B screw as, on Shimano stuff, it does bugger all (as rowlers said).
Just checked, and the upper jockey is about 5-6mm from the biggest cog. Changes are definitely on the firm/snappy side (which is good imo).0 -
I'm not touching the campy one, everything works and I'm done tinkering with it, so I cant comment on how effective it is. In terms of Shimano, I've only used 2300 and Tiagra but the b screw did nothing. :oops:0
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The screw is there for a purpose but if it is ineffective then I suspect that it is failing to find the small flat surface provided by the drop-out. It's sometimes necessary to place a small nut and lock this on the end of the screw in order to have it bear on the drop-out surface. This happens as frames do have differences in angles and in the past I've had to braze a larger platform on the drop-out.0
