Ultegra Rear derailleur b screw

hvm5

I replaced the cassette on my bike from a 11-28 to a 11-32. Didn't replace the derailleur or have the chain lengthened but it mostly works fine except when in the big big combination.

When I'm in the 34front 32rear, it's making a slight noise as if the jockey wheel is coming in contact with the 32t ring, it doesn't appear to be when I look at it but it's probably a bit close for my liking. I figured all I would have to do is adjust the B screw to move it further away but adjusting the b screw all the way in seems to do absolutely nothing. Am I missing something? This is the first shimano road bike I've owned, usually adjusting the b screw on my other bikes, moves the derailleur.

k-dog

It should move it - and you'll need to do it with that much of a change.

I'd want to look at chain length too - feels like you'll want an extra link or so.

arlowood

Yes your chain length should have been adjusted - calculator below suggests the an additional 1 inch would be needed to accommodate the jump from 28 to 32 largest sprocket

http://www.machinehead-software.co.uk/b ... hcalc.html

Also Shimano recommend the GS (medium cage) derailleur for the 11-32 cassette with a compact chainset. You are probably pushing things a bit trying to run the short chain on a short cage derailleur.

Firstly I would fit a longer chain and see how that goes - might be that the B-screw can then give you enough adjustment to have things running smoothly.

k-dog

If the screw won't move it far enough you can take it out and screw it in from the other side - gives a few mm extra.

dj58

You could try a longer B-Tension screw.

n3bur

hvm5 wrote:

I replaced the cassette on my bike from a 11-28 to a 11-32. Didn't replace the derailleur or have the chain lengthened but it mostly works fine except when in the big big combination.

When I'm in the 34front 32rear, it's making a slight noise as if the jockey wheel is coming in contact with the 32t ring, it doesn't appear to be when I look at it but it's probably a bit close for my liking. I figured all I would have to do is adjust the B screw to move it further away but adjusting the b screw all the way in seems to do absolutely nothing. Am I missing something? This is the first shimano road bike I've owned, usually adjusting the b screw on my other bikes, moves the derailleur.

Having the same problem here, b-screw not working as it should. It appears when threading it in it shifts off the little hook. Even when it's mostly out the tip of the screw sits only half on the hanger. What can I do to fix this? It's an Ultegra 6800 long cage derailleur on a Cannondale Synapse frame.

lesfirth

I have been fiddling about with b screws to run a 34t big sprocket with a 105 GS rear mech. I do not know about Ultegra but with 105 there is more than one GS mech. A 5700 and a 5701 and they are substantially different. I needed a 5701. As you have found out a longer B screw does not work. The angle it works at means it misses the rear hanger. I have used a countersunk head screw ,screwed in from the opposite direction so that the screw head rests on the hanger. It works great now.
If your chain is long enough to select big/big without a problem it will be OK as it is.

n3bur

Thanks for the response. What do you mean with a countersunk head screw? (English is not my native language). Can't I use the screw I have and reverse it?

k-dog

I would try that - you might want one with a slightly bigger head though - depends if that one is big enough to hit the right spot

lesfirth

n3bur wrote:

Thanks for the response. What do you mean with a countersunk head screw? (English is not my native language). Can't I use the screw I have and reverse it?

Sorry my IT skills prevent me posting a photo. A countersunk head has a bigger diameter then your existing screw.Google it for a picture.
Yes you can reverse the existing screw but in my case it only just touched the hanger. The countersunk head ( screwed in from the wrong side) made a better contact with the hanger.

svetty

Messing with the B-screw only works if the underlying problem is inadequate clearance between the sprockets and the upper jockey wheel. I'd make sure that this is your issue before spending time playing around with the B-screw.

In most instances the issue is with chain length IMO - but this is really only a problem in big-big which is easily avoided......