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Old 03-31-06, 04:53 PM   #1
bh357
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B-Screw Adjustment

I am not clear on the proper B-screw adjustment. Is the adjustment performed with the chain in the innermost (smallest) chainring? Park tool doesn't specify this. Also, should the clearance between the derailleur pully and cog be checked while backpedalling? If I'm in the innermost cog and chainring, my pully is contacting the cog when I backpedal. Would this be something to worry about.
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Old 03-31-06, 05:00 PM   #2
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You're talking about the inner chainring of a triple and the largest cog of a freewheel? Did you change something? Add a larger cluster, etc.?
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Old 03-31-06, 05:47 PM   #3
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Quote:
Originally Posted by bh357
If I'm in the innermost cog and chainring, my pully is contacting the cog when I backpedal. Would this be something to worry about.
Uh - that's exactly what you are trying to avoid by making the "B" screw adjustment. Pull your derailleur back until you gain some clearance between the cog and derailleur pulley.
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Old 04-01-06, 11:14 AM   #4
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Thanks. I replaced the derailleur cable. I don't know how it was before I replaced the cable. Today I tightened the B-screw further, and it's not rubbing at all now. In the smaller cogs, the pully is a good distance from the cog.
The only rubbing I was getting was when I backpedaled in the inner chainring and inner cog.
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Old 04-03-06, 06:51 AM   #5
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Is the B-screw adjustment supposed to be checked for clearance while backpedalling, or only when pedalling forwards?
Thanks.
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Old 04-03-06, 11:57 AM   #6
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Quote:
Originally Posted by bh357
Is the B-screw adjustment supposed to be checked for clearance while backpedalling, or only when pedalling forwards?
Thanks.
What is the number of teeth on the largest cog?
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Old 04-03-06, 09:04 PM   #7
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Sheldon has a good article about this.
http://sheldonbrown.com/derailer-adj....html#btension
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Old 04-04-06, 05:26 AM   #8
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Originally Posted by wagathon
What is the number of teeth on the largest cog?
The largest cog has 32 teeth, and the derailleur is a Deore. My bike is a 2005 GF Marlin, and these are the items that it came with.
I don't know if there was any contact between the derailleur and the pully before I replaced the cable, but after I replaced it, there was contact, but only when backpedalling in the small chainring, big cog position.
I tightened the B-screw enough to remove all contact between the derailleur and cog, but by doing that I created a sluggish upshift to the smallest cog, especially in the middle chainring (and to a bit lesser extent when in the large chainring).
The bike shifts good to the smallest cog when not being ridden (makeshift stand = hung from the rafters), and pulling and releasing the cable by hand to shift from the smallest to the next smallest cog. It is very hesitant to shift to the smallest cog while being ridden. All other shifts are great (indexing is able to be set perfectly, just not that last upshift).
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