Thanks for the suggestions William. Just for fun I ran down to the garage and filed a "smidge" off the bolt that holds the shift lever to the DT boss and was able to get the lever significantly tighter. I did a few laps up and down the hill in front of my house and no FD slippage.
Funny coincidence is that I shortened 3 other bolts on my AHH over the weekend and the file was still sitting on the work bench. --Andy On Monday, July 2, 2012 11:22:42 AM UTC-7, William wrote: > > Mike > > This is a very common issue with several very simple fixes. I apologize > in advance for a long post > > As you know, there's a spring in the front derailer that wants to pull the > chain down to the small ring. The only thing stopping that from happening > is the friction in the shiftlever. If there's more static friction in the > shiftlever, it'll keep the front derailer in place. If the force in the > derailer spring is stronger, it'll win and pull the chain over. When you > pedal out of the saddle, the frame flexes some and makes the cable a little > tighter a little looser in phase with your pedalling. If the friction in > the lever is just barely strong enough to hold the derailer in place, this > part can make the derailer walk down to where it's constantly rubbing and > requires you to pull the shifter again to take up the slack. > > This problem is more common these days because modern front derailers have > ridiculously strong return springs because of all the mashers who insist on > being able to downshift to a smaller chainring while hammering out of the > saddle. Furthermore, the lever arm on the ft derailer linkage is much > shorter today than in older derailers, making the front derailer 'stronger' > because of an increased mechanical advantage. This 'enhancement' developed > to get brifters to work. So the fixes can include: > > 1. If you have a 'modern' front derailer, consider swapping it with an > older design. One with a lighter spring and/or longer lever arm > 2. Get more friction out of your friction shifter. If you tighten up the > d-ring all the way, you should no longer even be able to move your shifter > in the downshift direction. If you can't do that, then you aren't really > tightening the friction part of your shifter. You've merely bottomed out > on the bolt and you are tightening against that. You need a shorter bolt, > or a slightly thicker friction washer inside. > 3. Another modern front derailer 'enhancement' is a SUPER narrow cage. > One of the consequences of that is you have to have your limit screws set > really precisely, and you have to slam the derailer against the limit screw > when you are in the big ring and a smallish cog. In this situation, the > tug-of-war is no longer the front derailer spring against the shifter > friction. It's an immovable object (the limit screw) against the friction > in your shifter. The limit screw always wins, and you'll always be able to > get a tiny bit of slack in the cable. To check if this is what you are > experiencing, deliberately back off the upper limit screw a lot. Like a > full 360 degree rotation. You'll have to be careful not to overshift when > you go into the big ring. When in the big ring, see if you can make the > rubbing happen. You might not be able to. If you find that backing off > the limit screw 'solves' the problem, then you'll be left trying to find a > balance where there's a combination of limit screw setting + technique that > keeps you from overshifting and avoids this phenomenon. Another surprising > fix for this particular corner case is flexier shift cables. People forget > how springy shift cables used to be. These days, they are super stiff in > tension to make indexing work. A springier cable can take the stress > cycles associated with pedaling without moving the shifter. It's hard to > find springy shift cables, these days, though. > > On Monday, July 2, 2012 10:48:44 AM UTC-7, Mike wrote: >> >> On Jul 2, 9:08 am, Scott Henry <ske...@gmail.com> wrote: >> > Just curious, is the front shifter slipping or is the front derailuer >> just >> > rubbing? >> > If it only happens during hard efforts, it may be due to frame flex >> rather >> > than shifter slip. I'm assuming you are in the big ring and try to >> hammer >> > when the frame flexes away and effectively tries to stretch the length >> of >> > the cable, due to the FD outer limit screw the FD can't move and thus >> pulls >> > the cable with moves the lever... >> >> I haven't ruled out frame flex being the culprit. I feel like I've >> talked with a number of people of varying sizes who have had this >> issue on various bikes. I've had it a bit with my LHT on sustained >> stand-up efforts. I may try adjusting the limit screw and see if that >> helps. >> >> I've thought about emailing Mark at RBW to see what he thinks. Also, >> I've thought about emailing Jan Heine, as I'm sure he has some >> insights. >> > >> > Just a thought as I hate when people blame their weight and then offer >> up >> > something like 185lbs. >> >> While 185 isn't necessarily clydesdale for my height (5'11.5"), it's >> still heavy enough to flex the frame I think and possibly be a >> contributing factor. >> >> > Cheers, >> > Scott (now I feel horrible at my 225lbs) Henry >> > Dayton, OH > > -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To view this discussion on the web visit https://groups.google.com/d/msg/rbw-owners-bunch/-/3y2x7hzR6yEJ. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. 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