Bicycle Mechanics - RD "b-tension" screw
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06-16-06, 09:04 PM
I've got a problem with my Ultegra 10 speed rear derailleur. I am unable to adjust the "b-tension" screw as per Shimano's instructions. Here's what i've done so far:
I moved the chain to the smallest chanring, and the largest gear. My idler pulleys have a lot of clearance between them and the largest rear gear. Shimano said one should get them "as close to each other as possible without touching."
I turn the B tension screw, and nothing happens. The idler pulleys are still far far away from the largest gear. I moved the screw through its whole range of travel (both ways), and nothing is moving. This is a brand new bike, supposedly set up properly by the LBS, so I have no idea why it isn't working. Any ideas?
06-16-06, 09:13 PM
Can you post a pic from the direct side view with the chain on those gears, and also with the chain in the big-to-big combo?
06-16-06, 09:18 PM
Unfortunately I don't have a digital camera (my girl is "borrowing" it for her trip). However, with the smallest chainring/largest sprocket combo, there is about 5mm of distance between the gear teeth. No amount of screw turning will get the RD to move at all. I can physically push the idler pulley closer to the largest sprocket, but it always springs back to its original position. It's almost like the spring doesn't have enough tension to hold the idler pulley that close to the large sprocket.
06-16-06, 09:22 PM
I was also thinking this:
Maybe the chain is a little too short from the factory, which physically won't allow the idler pulley to draw in closer to the cassette (no matter how much screw turning I do)
06-16-06, 09:40 PM
I was also thinking this:
Maybe the chain is a little too short from the factory, which physically won't allow the idler pulley to draw in closer to the cassette (no matter how much screw turning I do)Yeah, me too. What brand/model of bike is it, and I can at least scope out the design?
One option would be to remove the pulley cage from the forward knuckle of the derailleur and switch the spring to the higher-tension position. I haven't had the pleasure of dabbling with 10sp Ultegra so it's possible they don't have such a feature anymore, but I've used that in the past in situations where I wanted the upper pulley to sit closer to the cogs.
06-16-06, 10:04 PM
This is on a Motobecane Le Champion SL.
06-16-06, 10:21 PM
Ok, so like this, then:
Just checking something... the "point" of the B-tension screw is resting on the "claw" of the derailleur hanger, right? I took a picture, hope this isn't too dim... the tip of the screw should be resting on the "claw" of the hanger, circled in red there. If you can't see it well, try brightening the image in an image editor if you have one. I'm on my less-equipped PC right now or I'd do it for you.
When you adjust the B-tension screw, the metal thing that the screw threads into is supposed to move further or closer to the hanger's claw. I've seen where the metal thing manages to get hung up in a position where the B-tension screw isn't hitting the hanger, and then of course it has no effect when you adjust it, plus the B-tension spring is being held at a high tension to boot. So that's why I'm asking about that.
Also, try shifting to the small-to-small combo. If the derailleur's not very relaxed in that combo, then you might want another pair of links in the chain, but you don't want it on the verge of losing tensioning either.
06-16-06, 10:28 PM
Yes, the screw is resting on the derailleur hanger claw as you mentioned above. Also, my bike is just like the one you pictured above.
06-16-06, 10:32 PM
Hmm, then maybe see if you can add a couple links to the chain without the rear derailleur approaching a saggy-chain situation in the small-to-small combo. Or do Forward-Knuckle Surgery if you're game for it :)
That looks like a fun bike, I wish I still had a road-racer :beer:
06-16-06, 10:39 PM
I think I might do the knuckle surgery and see what happens. Hopefully I won't screw up anything too badly :D
Thanks for all the help though. You should look into getting another roadbike ;) I'm loving this one so far. Some claim that it's an el-cheapo frame, but I can't argue with the price ($1295) for all of the top-notch components that it came with.
06-16-06, 10:50 PM
I have an OK frame waiting in the wings, but I spent too much money on computer stuff to build it yet :( Misprioritization... oh well, the paint should be well-cured by the time I get it built, anyway.
one of the last pre-buyout '00 Paramounts
The way most Shimano derailleurs' front pivot is held together is with a 2mm setscrew that enters the knuckle near the upper pulley's axle bolt. You back it out a ways, and then the pivot can be pulled out of the knuckle. Good luck!
06-16-06, 10:58 PM
Thanks for the pointer, and good luck with that Schwinn. I like the color!
06-17-06, 07:21 AM
To get the derailleur pulley closer to the cogs, you unscrew the B-tension screw...
That's what I tried. I even backed out the screw ALL the way, and the pulleys still don't move.
Hmmm, could be your bike has a longer derailleur hanger than normal. Then again, 5mm is about the closest they come together anyway since the chain itself will sit in between and keep them apart. The real adjustment for the B-tension is to actually push the derailleur away from the biggest cog.
If you're on the large end of teh range allowed by the total chain-wrap amount, the big cog can actually make the derailleur pulley ride on the cog itself. You can verify this by shifting into the lowest gear without a chain in place and you'll see that pulley runs into the side of the cog when it should be clearing it completely. With a chain in place, the chain will actually push down the derailleur and allow the shift to occur. However, trying to shift off the largest cog can have the derailleur be stuck, there's not enough loose-chain to bend sideways to get the chain off the cog. So this is when you screw in the B-tension bolt enough to pull the derailleur away from the cog. If your set-up shifts fine in going from the biggest to next cog, I wouldn't worry about it.
06-18-06, 06:18 AM
However, with the smallest chainring/largest sprocket combo, there is about 5mm of distance between the gear teeth.
Honestly, I think that 5mm is a good amount of distance. If the jockey pulley gets too close to the cog you will feel a vibration as the chain runs over each individual cog tooth.
06-18-06, 12:43 PM
Thanks for the help guys. I think i'll take your advice and just not worry about it and RIDE!
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