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Old 03-12-10, 12:34 PM   #1
tass1
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Ultegra b-tension adjustment question

Question regarding the b-tension adjustment on my rear derailer. Background: Climbing in the granny gear, I noticed the chain would start to drop to the next gear. Not fully dropping, but just getting bumped every couple of revolutions. Last climb of the day, so I stopped with the granny gear and continued on. It shifted fine in both directions.

Brought the bike home and checked Shimano's tech docs. It appeared to me that the jockey pulley was too close to the largest cog. I tried adjusting it using the b-tension screw, but the screw seemed to have no affect on way or the other, full in or out.

I am new at bicycle maint., but willing to learn and would rather do it myself.

Am I overlooking an adjustment or maintenance item? I tweaked and reset the high and low limits after the failed adjustment. Probably pointless, but they were numbers 1 and 3 on the shimano service instructions, before the b-tension adjustment.

All component are 5500 series 105, with the exception of a 6500 series rear derailer. 9-speed triple. Cannondale. Probably around 700 miles plus a light winter on the trainer. Not sure on previous maintenance as I bought it used with very low miles.

Thanks in advance.
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Old 03-12-10, 12:40 PM   #2
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A good picture showing the area where the B screw meets the RD hanger would be helpful. I've used a 6500 on a early Cannondale frame with no problems. Is the B screw actually meeting the frame/hanger tab?
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Old 03-12-10, 12:43 PM   #3
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Either you don't have enough cable tension (doesn't seem to be the case since it other shifts fine) or your low limit screw is set too far in (most likely cause). Is it more difficult to select the largest cog than the previous one? That would be a certain indication that it's a limit screw problem. Back the screw out by 1/4 turn and the problem should go away.

Re: b-tension screw, so long as the upper pulley is close but not touching the largest cog, don't bother messing with it.
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Old 03-12-10, 12:58 PM   #4
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A good picture showing the area where the B screw meets the RD hanger would be helpful. I've used a 6500 on a early Cannondale frame with no problems. Is the B screw actually meeting the frame/hanger tab?
It appeared so, yes. I'll try and verify with a pic tonight.
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Old 03-12-10, 01:01 PM   #5
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Either you don't have enough cable tension (doesn't seem to be the case since it other shifts fine) or your low limit screw is set too far in (most likely cause). Is it more difficult to select the largest cog than the previous one? That would be a certain indication that it's a limit screw problem. Back the screw out by 1/4 turn and the problem should go away.

Re: b-tension screw, so long as the upper pulley is close but not touching the largest cog, don't bother messing with it.
Pedaling backwards, it was touching. Or, at least close enough that both pulleys were vibrating (not sure if that's the right description, but the movement wasn't smooth).
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Old 03-12-10, 01:03 PM   #6
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Pedaling backwards, it was touching. Or, at least close enough that both pulleys were vibrating (not sure if that's the right description, but the movement wasn't smooth).
How about pedaling forward? Who's back-pedaling while climbing?
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Old 03-12-10, 01:05 PM   #7
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How about pedaling forward? Who's back-pedaling while climbing?
Hehe...in my basement at this point. It seemed to replicate the problem fairly well.
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Old 03-12-10, 01:28 PM   #8
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The b screw on my 600 derailleur does stuff-all too. Maybe the upper spring is prone to losing tension...

How old is your derailleur, BTW?
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Old 03-12-10, 01:35 PM   #9
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Hehe...in my basement at this point. It seemed to replicate the problem fairly well.
So do you have clearance when pedaling forward or not? Which problem was replicated when back pedaling, the chain jumping cogs or something else?
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Old 03-12-10, 01:35 PM   #10
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The b screw on my 600 derailleur does stuff-all too. Maybe the upper spring is prone to losing tension...

How old is your derailleur, BTW?
It's stock off of a 2006. I could manually pull it back some and it would stay out of the way until I shifted off and back on. There's been very little maintenance done, besides lubing the chain and the occasional cleaning. Anything that I should clean that may prevent it from returning? It was cruddy out yesterday with the snow melt.
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Old 03-12-10, 01:38 PM   #11
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No clearance when pedaling forward either. I mentioned the back pedal as that was in the instructions on the tech sheet. Sorry for the confusion. It would not fully jump cogs. Just a little bump and it would correct itself before falling off.
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Old 03-12-10, 02:25 PM   #12
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Anything that I should clean that may prevent it from returning? It was cruddy out yesterday with the snow melt.
You could try disassembling the pivot and cleaning it (it's held together with a circlip), but I'd be surprised if that helped... you might find a second hole you can put the spring in to tighten it up, though.

But be warned; getting the pivot back together can be kinda tedious.
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Old 03-12-10, 03:35 PM   #13
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No clearance when pedaling forward either. I mentioned the back pedal as that was in the instructions on the tech sheet. Sorry for the confusion. It would not fully jump cogs. Just a little bump and it would correct itself before falling off.
Ok, well turning the b-tension screw in should net you more clearance, though that shouldn't have anything to do with the chain jumping off the cog (that's more likely the low stop screw). If the derailler has seen a lot of bad weather, take Kimmo's suggestion of cleaning it up first before driving yourself nuts trying to adjust a binding derailler (BTDT). I've solved many a shifting issue by lubing derailler pivots.
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