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SRAM FD rub - can't solve.

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SRAM FD rub - can't solve.

Old 03-12-14, 04:46 PM
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nayr497
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SRAM FD rub - can't solve.

I'm having trouble getting my SRAM drivetrain to run smoothly.

I've set everything up following their instructions and have tried to fine-tune things, but I'm still getting FD rub on my chain when I get to middle of the cassette and from there on out. Seeing if anyone can sort me out.

- SRAM Red Ti FD (I know these are flexible and lots of people don't like them, but I've had this bike running smoothly in the past, but now can't seem to get it sorted)

- 42x38 rings up front, 12-28 in the rear
- Force RD

I haven't moved the FD height since when I had things running well. I now have the H-limit screw nearly all the way out, but I'm still getting rubbing. If I hold the left shifter paddle, the FD cage will clear the chain, but once I let go, it starts to rub again.

I'm out of ideas. I've tried micro-adjusting it, but can't seem to get it.

Ideas welcomed!
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Old 03-12-14, 05:14 PM
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Logically, if you can get the derailleur to move out far enough not to rub by holding the paddle the problem cannot be the limit screw. If you shift and the derailleur does not go out to that screw then there are only two possibilties:

1. The cable is not tensioned enough.
2. The cabel is tensioned too tightly, so that when you move the derailleur out to the stop the lever has not yet reached the detent that holds it in the high gear position.

Start over from scratch if necessary, including height and rotation.
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Old 03-12-14, 05:20 PM
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Ah, for some reason I've been so focused on the limit screws I've overlooked cable tension. How stupid!

I'll work on the cable tension before I start from scratch. I installed new shifters recently and the FD was working fine (not rubbing) before so I don't think it's height/rotation.

Thank you for the feedback!
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Old 03-12-14, 05:33 PM
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BTW- if you're stringing a new cable, consider an in-line adjuster. These make it far easier to fine tune trim for FDs, especially with triples.
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Old 03-12-14, 05:40 PM
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Good suggestion, FB.

This is a double on a cross bike. I do have a barrel adjuster at the cable stop on the DT. I'm going to work with that and see if I can sort things out.

Thanks for the replies!
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Old 03-13-14, 09:21 AM
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The pre-yaw Red front shifter has three positions; low, high, and a trim position just inside high. Perhaps it's not holding in the high position and is dropping to the trim position.
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Old 03-13-14, 10:45 AM
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Thanks, Looigi. Yep, it does have three positions. These are NOS Red shifters that I've had for just a few weeks. SRAM warrantied some Force shifters for me, didn't have any of those on hand, so upgraded me. Nice! The shifters are working just fine.

I was able to eliminate the FD rub with a few turns of the barrel adjuster. No more rub! Thanks for the great advice.

Since I'm asking...when in the 28 cog in the rear, the chain doesn't really want to stay there, it wants to jump back down to the 26 (27?). I know a 12-28 is kind of a weird range but, do I need to put a bit more or a bit less tension on the RD cable? I'm thinking less, it must have too much tension and it's not happy stay there. I think the L-limit screw it set just fine.

Thanks!
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Old 03-13-14, 03:55 PM
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Sram RD shifting is a bit different when you get to the largest cog. With Shimano, Campy, and even Microshift you have separate levers to shift up or down. With Sram double tap, there's only one. So, when in the biggest cog, if you push the lever until it clicks and release the lever, it'll drop to the the next smallest cog. This is inconvenient if you are in the biggest cog, don't know it, and try shifting to a larger cog only to have it drop to a smaller one. The way Sram gets around this is you can push the lever farther than the first click to a second click and when you release the lever it will stay in the largest cog. Since you're up against the stop, pushing the extra distance to the second click can be quite hard. The trick is to back out the low limit screw ~1/4 turn to allow a bit of over travel of the RD. Make sure it's no where near enough to allow over shifting into the spokes however.
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Old 03-13-14, 06:07 PM
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Goodness, that is a thorough answer! Thank you.

I have played around a bit with the SRAM stuff and yeah, I kinda understand the last click mechanism. Will check this out tomorrow and hopefully sort it all out.

Took it for a short spin today, no FD rub, which is great. Shifting well in the back, just not happy in the 28.
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Old 03-14-14, 08:00 AM
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If it's not staying in the big cog, it's possible that you're off in cable tension (length, actually) by one gear. Shift to the smallest cog, pull on the cable (where it's accessible) sidewise like plucking a guitar string, then try to shift to yet a smaller cog. This puts the shifter in the highest gear (smallest cog). If the cable is loose and downshifting doesn't move the RD to the second cog, the tension is too loose by one gear. If that's the case, put the shifter in the highest gear, screw the cable adjusters in, and take up the slack at the cable fixing screw on the RD.

Last edited by Looigi; 03-14-14 at 08:03 AM.
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