front derailleur cage tweaking

[Leslie]

Ok,

One bit of a tuning issue I'm having with the new bike, thought I'd see what the group suggests...

Setup:  56 Bombadil 650b frame, 107 SKF BB, with a Sugino XD2 crank (48/36/24 rings).  Rings clear the frame nicely (more clearance than my Ram has running a DuraAce Octalink triple). 

The front derailleur is a Shimano Deore LX, and I'm using DA 9sp barcons.  The cage on the FD is for a triple, for a 48tooth ring.  It has a good matching arc, and the tail-end of the cage clears the chainstay, no problems there.

The problem I'm having is, on the granny ring, and the amount of travel in shifting (or rather, the zone the derailleur travels when shifting).

I can center it up on the middle ring, and shift up to the big ring, no problem, back and forth.  But, it's hard to get it to shift all the way down to the granny.  And, it's really easy to overshift on the upshift, clean past the big ring and take the chain off the front, dropping onto the crank arm.

Trying to adjust the tune, cable, set screws, etc., with the derailleur all the way towards the inside, the cage is just keeping the chain from easily dropping to the granny. 

I'm half tempted, to try to but a bit of a bend into the cage, to get the bottom of it to sit closer in towards the seat tube; then, have the shift lever not bottomed out, but moved further in, before I lock down the cable, so that when I shift up, it runs out of shifting range before it throws the chain.

Does that make sense?

[Seth Vidal]

Have you checked the angle of the fd to the chain/frame. The park tool
big blue book has a useful guide on tuning this up.

http://www.parktool.com/blog/repair-help/front-derailleur-adjustments

-sv

[Michael Hechmer]

When you shift up to the big ring, how close is the derailleur to the ring.  You want to get it within 5mm.  The other issue may be that the BB is too long.  You mentioned having lots of clearance, you probably should have very little clearance.  Do you have the option of experimenting with a shorter BB?  I had a similar problem on my tandem, w a super record derailleur, and found that a shorter BB & a ring with ramps & pins solved the problem.

Michael

[Leslie]

On Wednesday, May 23, 2012 3:31:05 PM UTC-4, MichaelH wrote:
> When you shift up to the big ring, how close is the derailleur to the ring.  You want to get it within 5mm.  The other issue may be that the BB is too long.  You mentioned having lots of clearance, you probably should have very little clearance.  Do you have the option of experimenting with a shorter BB?  I had a similar problem on my tandem, w a super record derailleur, and found that a shorter BB & a ring with ramps & pins solved the problem.
>

New derailleur, had the block with the guide sticker in place, I centered it between the lines, so it should be 2-3mm; the BB is a 107, there isn't shorter. (I actually wondered if a longer one would put the crank a bit further out, so it'd actually line up on the granny better, but, it's an SKF, and I like the Q, so, I'd rather deal w/ the derailleur instead...

Seth, hadn't seen that; I'd thought of trying to take the shell shims for the clamp, and putting both on the far side, so it'd shift it closer to the seat post, since the adjustment screws didn't shift it enough, but I'll go through that and see if I can get it to behave better... Thx,

[Leslie]

Whoo-boy...

Okay, I've read though that, but still didn't solve it...

Derailleur is, 2mm, above the big ring when out that far. Cage is correctly rotated, so the outer plate is parallel to the chain. But with no cable tension, even with the cable removed and the L-screw turned to ring the plate inward as far as possible, it's still not inward enough...

Thoughts I've had:
Shim the derailleur to angle it such that, keeping the cage parallel to the chain, the bottom edge of the inner plate is swung towards the seat post;
Remove the seat post shim from the derailleur clamp, then double it on the left side, leaving it off the crank side;
Bend the cage so that it is closer to the seat post;

Any better ideas?

[Mojo]

Leslie,

 

sometimes a bit of 'cold setting' of the derailer cage can improve its performance. Perhaps try bending the lower portion of the outer cage wall inward a bit to give it a bit more punch to the downward trajectory.

[Joe Bernard]

The double-shim on the non-drive side may help. It sounds like your derailer is struggling with the short BB.

 

Joe Bernard

Vallejo, CA.

[René Sterental]

I think you need a wider BB. AFIK, the XT derailers are not such a good fit for the Sugimo cranks since they expect the wider Q from the Shimano modern MTB cranks. 

A new compatible  derailer from Riv would be the other option I'd suggest if you want to preserve the current BB. 

I would caution against doubling up the shim on one side. You'll loose the roundness of the internal surface and the pressure on the seat tube would be uneven. 

René 

[PATRICK MOORE]

Q doesn't relate (much*) to proper ring position with flared cranks.

Bending the derailleur cage can lead you into a vast thicket of trial
and error and more error until you finally die howling in frustration
and anguish, but perhaps one could think of bending the outer forward
tip of the d cage just a wee bit.

*Q is affected largely by arm flare. That's why you can have a 145 mm
bb and a 160 mm Q, or a 113 mm bb and a wider Q on the same bike with
different crank designs (as I've done).

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[Jeremy Till]

Yeah, I concur with what others have said.  If it's not far in enough with the limit screw all the way out and the cable slack, you've got the wrong derailleur.  It's true that contemporary MTB triples are much farther out than an XD on a 107mm BB would be, so that's probably the issue.  I'd try a road-type derailleur, whatever Riv recommends for that setup.

On Wednesday, May 23, 2012 7:21:34 PM UTC-7, Leslie wrote:

[Steven Frederick]

Try a BB spacer on the driveside to bring the granny ring out a little bit?  Good luck!  Problems like this drive me nuts.

Steve

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[Leslie]

And, Steve was the winner! Definitely one of those, why didn't I think of that, moments...

I picked up a 2.5mm BB spacer, pulled the crank, pulled the BB out, dropped the spacer on, BB back in, crank back on, and tweaked the cable tension, dialed the L and the H screws a tad...

Beautiful! I can now shift from to the granny w/ no rubbing, and to the big ring, w/o it continuing on and off onto the crank arm... Excellent suggestion!

Thanks!!!


+ + + +

Now, while dealing with this, I've had an 'incident' that irked me a bit. Not an incident, per se, but, one of those not what you expected LBS instances....

Once I read Steve's suggestion Saturday night, I was eager to get to the LBS to grab a spacer to give this idea a whirl. Well, the LBS in town was closed Sunday, and also on Monday for the holiday. So, Tuesday after work, I popped in to get a spacer.

Now, in my town, there is one bike shop. Bristol has two (one is MSL); Johnson City has two; then there's two others that i like, each in a small town between the bigger towns. But, I try to start local instead of driving further than need be, so I start in town. The guy who owns it is nice enough, actually opened the shop close to 40 years ago. Mostly a Trek/Cannondale shop, assembles new bikes and rolls them out the door, typical non-Rivish accessories, and do some repairs/tune-ups, etc. He has a few folks who work there part time as mechanics, one happens to be an old friend from college, but on this particular day, I was talking w/ another mechanic. He and I had had small talk before, but, this was the first time I was in *need* of a very particular something, and working w/ him specifically. He was in the middle of dialing in some new C'dale road bike, a 2x10 compact double w/ 700c-23 tires. I tried to asked for what I wanted, and got shot down: a triple is old, should go w/ a 2x10 set-up, I am using an old crank that I should junk, a square-taper BB is antiquated, my derailleur must be completely wrong if I'm having troubles, etc. I thought, I must've misspoke, and tried to re-explain, and he pretty much said, look, I told you a spacer is just wrong, you just want me to tell you you're right when you're not, you need to get some new parts and do it right....

I'm using a new Sugino crank, a new SKF BB, a Shimano LX triple derailleur, it's not like any of it was old or junk; but he kept saying a Sugino was old, that it became obsolete 20 years ago, and I shouldn't be trying to reuse such old parts.... Yet he said I should pitch my triple and go w/ a compact double, and a new cassette to go with.... Gack!!!

I tried to not argue, just kinda acted reflective, mulling it over, then slid on out the door, and had to drive to the next town over to its LBS. Nice guy there, he came over to see what I needed, I explained to him what I was trying to solve, what I needed; a minute later, he came back with a couple of spacers for me.

Was tied up most of the week, but finally had time tonight to put it on, and prove that it was the right solution. So....

Moral of the story: Although there's an LBS here in town and I think the owner's a nice guy, I'm probably going to jump in the car and drive 30 minutes to go to the next town, when I need something quickly from an LBS that I don't want to wait on to get shipped to me... It's a shame, really, but, when faced with such, well...

Anywho...