Rear derailleur makes chain rub against sprockets

[rliu]

Hi all I am building up a bike myself for the first time and finding myself lost in terms of how to set up the rear derailleur. I am running full Ultegra group with 53/39 chainset and 11-28 cassette with a short cage derailleur. In addition to the fact that the top jockey wheel rubs against the sprockets on every sprocket, I am also unable to get the chain onto the smallest two sprockets and also the chain goes completely slack if I put it on the small chainring. I have tried adjusting the H and L limit screws and also the B screw, and even followed tips on other forums of inserting the B screw backwards to give the rear derailleur more tension.

2 photos:
http://www.flickr.com/photos/rliu/sets/72157639306453493/

 

[Rickshaw Phil]

Those photo links throw up a 404 error for me.

From your description the first thing that springs to my mind is that the chain may be too long. How did you judge the length?

The fact the top jockey wheel is touching the sprockets does suggest there is still an issue with the B screw set up. There are various "how to" videos available that may help with this:

View: http://www.youtube.com/watch?v=SkzvfCaIbyQ


I hope this is of some use.

 

[rliu]

Thanks very much Phil, I have re-linked the photos: http://www.flickr.com/photos/rliu/sets/72157639306453493/
I had used a chain length calculator which said 55 links and that's what I have at the moment. I did have it at 56 initially. Removing the extra link did not make a difference.

 

[Whobiggs]

I put the chain on big ring and biggest cassette sprocket (not through the mech) and add 3 rollers if using a quick link, 4 if rivetting.

I have never seen a chain length calculator, how does it know how long your chainstays are? Wheelbase on my Dahon is about 2" longer than my Schwinn!

 

[rliu]

I put the chain on big ring and biggest cassette sprocket (not through the mech) and add 3 rollers if using a quick link, 4 if rivetting.

I have never seen a chain length calculator, how does it know how long your chainstays are? Wheelbase on my Dahon is about 2" longer than my Schwinn!

http://www.epicidiot.com/sports/chain_length_calculator.htm the chainstay length is a variable input.

 

[Stonechat]

Only changed a link chainonce and that was before computers around so just used common sense in chain length

 

[Whobiggs]

That's a good website, I'll make a note of that thanks.

http://sheldonbrown.com/ is another good source of information I use often.

 

[RecordAceFromNew]

The photos aren't taken square from the side so it is a little hard to see but is the B screw catching the tab on the dropout like pic below?

If that is fine, from the middle photo I can't see how the chain can be the right length unless the mech is faulty. What is the distance between the middle of the crank bolt/bb to the middle of the rear wheel axle?

 

[Rickshaw Phil]

Thanks very much Phil, I have re-linked the photos: http://www.flickr.com/photos/rliu/sets/72157639306453493/
I had used a chain length calculator which said 55 links and that's what I have at the moment. I did have it at 56 initially. Removing the extra link did not make a difference.

Thanks for sorting the links. Now I can see the pictures it does look a lot like the chain is too long. The method that @Whobiggs mentions: running the chain big to big plus 3 rollers without going through the mech, is the method I use with no problems.

The Shimano tech document shows that when in the big ring and smallest rear sprocket the jockey wheels should be in a line 90 degrees from the ground. It would be worth checking if yours matches this.

 

[grimpeur]

<<the top jockey wheel rubs against the sprockets on every sprocket>>
Something must be fundamentally wrong with what you are doing. If this is happening with the chain properly fitted and the rear mech cable tensioned well it shouldn't be, B screw adjustment shouldn't make THAT much difference.
Is wheel sitting correctly in dropouts, b screw seated against tab on mech hanger?

 

[baljit]

Thanks for sorting the links. Now I can see the pictures it does look a lot like the chain is too long. The method that @Whobiggs mentions: running the chain big to big plus 3 rollers without going through the mech, is the method I use with no problems.

The Shimano tech document shows that when in the big ring and smallest rear sprocket the jockey wheels should be in a line 90 degrees from the ground. It would be worth checking if yours matches this.

phil

Thanks for sorting the links. Now I can see the pictures it does look a lot like the chain is too long. The method that @Whobiggs mentions: running the chain big to big plus 3 rollers without going through the mech, is the method I use with no problems.

The Shimano tech document shows that when in the big ring and smallest rear sprocket the jockey wheels should be in a line 90 degrees from the ground. It would be worth checking if yours matches this.

Hi Phil,
I hope you can help me. Putting the chain in big/small has the two pulleys in-line and at 90 degrees to the floor. B-screw is at its max. But top pulley still touching the cog when in small front/ large rear. I think the problem started when I moved the bike without the rear wheel attached but I can't see that anything is bent and the indexing isn't affected at all. Any ideas? Thanks in advance.

 

[User6179]

One of the springs in the rear mech might need replacing but I think your chain might be to long .

 

[Rickshaw Phil]

Hi Phil,
I hope you can help me. Putting the chain in big/small has the two pulleys in-line and at 90 degrees to the floor. B-screw is at its max. But top pulley still touching the cog when in small front/ large rear. I think the problem started when I moved the bike without the rear wheel attached but I can't see that anything is bent and the indexing isn't affected at all. Any ideas? Thanks in advance.

Hi and Baljit.

I shall attempt to help, but could do with a bit more info:
When you say that the problem started when you moved the bike without the wheel attached, what happened? Did anything get knocked?

What is the bike and what gears? Have you fitted any new parts?

Is the B screw engaging properly with the tab on the frame as shown in the photo posted above by @RecordAceFromNew?

Even though the indexing still works for you my initial thought is that something has got bent or dislodged as it's not usual to have to adjust the B screw much, if at all, once the bike is set up.

 

[baljit]

One of the springs in the rear mech might need replacing but I think your chain might be to long .

Thanks, i'll take it to be checked

 

[baljit]

Hi and Baljit.

I shall attempt to help, but could do with a bit more info:
When you say that the problem started when you moved the bike without the wheel attached, what happened? Did anything get knocked?

What is the bike and what gears? Have you fitted any new parts?

Is the B screw engaging properly with the tab on the frame as shown in the photo posted above by @RecordAceFromNew?

Even though the indexing still works for you my initial thought is that something has got bent or dislodged as it's not usual to have to adjust the B screw much, if at all, once the bike is set up.

Gears are compact shimano with 12-27. I moved the bike in my car. Usually i leave the rear wheel on, but this i took it off too in order not to have to put the seat down. It's possible the rear mech was touching/touched the seat back :-( i guess thats whats done it!

Thanks for the welcome. I've been lurking a long time!