Rear cog/cassette contact problem

[HNS]

XTR rear derailller. Specialized Stumpjumper Comp Disc. 3 front chain rings, 9 rings on the rear cassette. With the derailler set to the largest chain ring, the derailler cog nearest the cassette is squeezing the chain and the cog comes in contact with the chain ring/cassette. I have disassembled the derailler and set the spring for the arm to the highest tension setting and that didn’t fix it. I tightened the "B" (?) screw to increase the tension of the entire derailler to bring the cog off of the chain ring/cassette and that didn't fix it either. What else can I do to get the cog off of the cassette?

Derek
Think

 

[Juba]

I have read through your post a couple times, and I am confused.

Chain ring = what are bolted to your crank arms.
Cassette = the stack of gear cogs attached to your rear hub.
Cog = one of the gears in your cassette.
Pulley wheel = the jockey wheels on your derailluer.

Are you saying when you are in the smallest chain ring and largest cog (which would be 1st gear), the pulley wheel teeth hit the teeth on the cog? If screwing the B adjustment screw all the way in is not doing the trick, I have to ask a couple additional questions:

1) Are you sure you chain is the correct length? If your chain is too long, your derailleur might not have enough spring tension to keep the pulley wheels off the largest cog.

2) Have you bought either the rear derailleur or a new cassette, and if so are you sure that the derailleur is rated for that cassette? Some XTR derailleurs are only rated to handle a max of a 32 tooth cog, and if your cassette has a 34 tooth cog, your rear derailleur might not have enough spring tension.

If it is not either of these things, you might be able to find a slightly longer B adjustment screw either from a different derailleur or just a bolt laying around.

Cheers,
Juba

 

[HNS]

"Chain ring = what are bolted to your crank arms.
Cassette = the stack of gear cogs attached to your rear hub.
Cog = one of the gears in your cassette.
Pulley wheel = the jockey wheels on your derailluer."

OK, I got the terms off a bit. The pulley wheel closest to the cassette is hitting the cassette when the chain is on the middle chain ring on the front and the largest cog on the cassette.

"Are you saying when you are in the smallest chain ring and largest cog (which would be 1st gear), the pulley wheel teeth hit the teeth on the cog?"

Yes

If screwing the B adjustment screw all the way in is not doing the trick, I have to ask a couple additional questions:

"1) Are you sure you chain is the correct length? If your chain is too long, your derailleur might not have enough spring tension to keep the pulley wheels off the largest cog. "

It is the chain that came w/ the bike. Got it about 3 weeks ago. Same derailleur and chain, stock.

"2) Have you bought either the rear derailleur or a new cassette, and if so are you sure that the derailleur is rated for that cassette? Some XTR derailleurs are only rated to handle a max of a 32 tooth cog, and if your cassette has a 34 tooth cog, your rear derailleur might not have enough spring tension."

OEM parts

"If it is not either of these things, you might be able to find a slightly longer B adjustment screw either from a different derailleur or just a bolt laying around."

I though about that, but because the angle that the b adjustment screw goes through the derailleur, it won't take much more length before the screw misses it's contact point on the derailleur.

"Cheers,
Juba"

Thanks. I'll look for a longer screw, which would fix it, if it can hit the contact point on the derailleur. Is it possible to adjust the internal tension of the spring inside the derailleur where it attaches to the frame? (Similar to adjusting the spring tension of the arm w/ the pulleys on the derailleur)

Thanks,

Derek

 

[Juba]

It is the chain that came w/ the bike. Got it about 3 weeks ago. Same derailleur and chain, stock.

Does not mean the chain is the correct length. The Specialized I bought in March of this year was one link too long. Take your chain off and wrap it around the largest cog and largest chain ring, without threading it through your derailleurs. Measure which link on the chain would be a perfect fit to wrap around, and then add one link to get the proper size of the chain. One link is actually two segments (a pair of inner plates and a pair of outer plates).

Is it possible to adjust the internal tension of the spring inside the derailleur where it attaches to the frame? (Similar to adjusting the spring tension of the arm w/ the pulleys on the derailleur)

No, there is not. The spring is too strong to rotate it an extra 360 degrees, and there is only one hole drilled for each end of the spring, unlike the tension arm spring, which has two holes on one of the sides.

Hopefully the longer B screw will do the trick. It worked for me when I back when I was using a max 30 tooth XT derailleur with a 12-32 tooth cassette.

Cheers,
Juba

 

[HNS]

Hopefully the longer B screw will do the trick. It worked for me when I back when I was using a max 30 tooth XT derailleur with a 12-32 tooth cassette.

Cheers,
Juba

The LBS had a neat trick, reverse the "B" adjustment screw so that the head of the screw rests against the contact point on the derailleur. Fixed the problem.

Thanks for your help,

Derek
Think

 

[closesupport]

I have read through your post a couple times, and I am confused.

Chain ring = what are bolted to your crank arms.
Cassette = the stack of gear cogs attached to your rear hub.
Cog = one of the gears in your cassette.
Pulley wheel = the jockey wheels on your derailluer.

Are you saying when you are in the smallest chain ring and largest cog (which would be 1st gear), the pulley wheel teeth hit the teeth on the cog? If screwing the B adjustment screw all the way in is not doing the trick, I have to ask a couple additional questions:

1) Are you sure you chain is the correct length? If your chain is too long, your derailleur might not have enough spring tension to keep the pulley wheels off the largest cog.

2) Have you bought either the rear derailleur or a new cassette, and if so are you sure that the derailleur is rated for that cassette? Some XTR derailleurs are only rated to handle a max of a 32 tooth cog, and if your cassette has a 34 tooth cog, your rear derailleur might not have enough spring tension.

If it is not either of these things, you might be able to find a slightly longer B adjustment screw either from a different derailleur or just a bolt laying around.

Cheers,
Juba

are you using a normal chain, narrow 9speed chain, or a (super narrow chain -
XTR dura ace)? fi your using the correct chain then, set your chain on the largest front chainring and the largest rear cog, when your chain is on your deraileur should hang 90 degrees not flopped back or pulled forward, if it isn't then you will not have enough tension in you chain in smaller gears.

have you tryed seeing if you can get a longer rear mech hanger made. other than that i think maybe you will have to change your rear cassette.

 

[Juba]

The LBS had a neat trick, reverse the "B" adjustment screw so that the head of the screw rests against the contact point on the derailleur. Fixed the problem.

You gotta love bike techs, especially the guys that have been around for a bit, they always have a new trick up their sleeves. Flip the screw around. So simple, so cost effective yet so functional. I bow to the guy who thought that one up, and bow to you for passing it along.

Cheers,
Juba