Adjusting Your Limits
November 6th, 2007 by Arleigh Jenkins
First learn what limit screws are.
Rear Derailleur - I first loosen the fixing bolt for the derailleur cable so it has no affect on the derailleur. Now I simply pedal with my right hand and with my left push the derailleur carefully up towards the wheel (or pull down if you have a reverse rise.) When you are closest to the wheel you don’t want the derailleur to rub the spokes or push the chain off that last cog. When you are furthest from the wheel you want the derailleur pulleys to line up under the last cog. I also listen when it is in this position, especially with SRAM as aligning it right doesn’t always make it silent. Play with it at 1/8 of a turn increments when you are pedaling . It should be almost dead silent when you are in your big ring up front and that cog.
Front Derailleur - Shift your rear derailleur into the largest cog in the back (after you check the rear derailleur limit screws.) Shift the front into your smallest. You should have only a few millimeters of room. On the picture at the right I would actually have it a bit closer. This is so when you are shifting from your middle to your smallest the chain doesn’t jump off into your frame. Now shift into the middle ring, shift your rear derailleur into the smallest cog and grab your front derailleur cable with your hand and pull until the derailleur stops. If the derailleur stops and the chain is in the big ring but rubbing the front derailleur - your high limit screw needs to be backed out. If the derailleur over shifts and the chain wants to shift off - screw the high limit screw in till there is barely any room between the chain and derailleur.
This post is part of my on going build up and review of the ‘08 Trek Fuel EX 5.5. Check it out.
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I have no problem with the limit screws, but I just can get the adjustment correct with the B screw or would it be the adjuster barrel?
shifting down is fine, hesitates, double shifts, and has trouble finding the gear in the middle gears, in addition, I have adjusted it so much my B screw is 90% stripped.
HELP
Your b screw doesn’t have to do with fine adjustment, that has to do with your derailleur and how far it sticks off your cassette. I will explain this more in a posts next week, but the B screw just “lifts” your derailleur away from the last cog, so that your pulley’s aren’t rubbing the cogs.
If you are having shifting issues only in your middle gears I would check out your derailleur hanger for alignment. http://bluecollarmtb.com/2007/08/26/hanger-alignment/
Another thing to check is if your cables are well lubed, and pull through the housing with no kinks or hold ups. But it honestly sounds like your hanger or derailleur are slightly bent.
I get good results with setting the B-tension as high as possible without the guide pulley getting so close to the largest cog that it “flutters” as the chain rotates.
On my two bikes, this means two things:
1. The MTB commuter with the 12-23 cassette and a Deore der gets the tension set as high as possible. This der was meant to be used with a larger cogset.
2. The road bike with the 12-32 mtn cassette and the medium cage Sora der gets the tension set as low as possible since 32T exceeds the intended Sora design limit by 5T. It still flutters a little.
SRAM’s specifications require the high pulley’s inner edge to line up with the high cog’s outer edge, this putting the pulley a little closer to the frame than it would with shimano. The low pulley is normal- centered on the low cog. Adjustment from those positions compensates for misaligned derailluer hangers. OK. I’m bored!