[rlong]

Hello everyone,
Odd question here. My new Pilot 5.0 has a 105 t front derailer (52/42/30) and it drops the chain off the inside chainring at the most inopportune times. I cannot adjust this out, as I already have the derailer just slightly rubbing against the ring. So it irks me that my tandem with 50/36/26 and a deore lx f derailer, never drops the chain off the inside. Whats up with this? Any suggestions? ChainWatcher is out due to the thickness of the carbon tubes at the bottom bracket and I wouldn't drill it to mount anything either for obvious warrenty reasons.

I know that 105t derailers are used on tandems, and likely with the same, or close to same chainring setup. I really am at a loss on this one and the LBS where I bought it hasn't been able to fix it either.

Help!!
rlong

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[ElRey]

I've got a 105 triple front and it never drops the chain.

[TandemGeek]

I really am at a loss on this one and the LBS where I bought it hasn't been able to fix it either.

Try another LBS... Not to diminish your frustration, but there's nothing magical about these things. You align the cage with the big chain ring per the spec sheet (1-2mm vert. clearance & parallel), you make sure the cable is attached to the correct side of the pinch bolt, you set the upper and lower stops, and then fine tune the cage position / travel for the trim positions with the barrel adjusted on the downtube cable stop.

The only other thing to consider in your troubleshooting is your shifting technique. If you are running the chain up the cassette to the largest cog in your big or middle ring and then shifting to the middle or granny once you find yourself still struggling on a steep climb, the heavily loaded drive train will "slip" past the chain rings. Although all the cogs are there, it's best to try and make a point of working the lower 1/2 of the rear cassette with the big chain ring and the middle 1/2 with the middle and to only use the largest cogs when you know you can complete the climb without using the granny. If you'll need the granny, get there while you are still carrying a high cadence and before you're in the two biggest rear cogs.

[Retro Grouch]

How's the shift quality?

I've worked with a couple of 105 triple front derailleurs that seemed to bind up and then, when it finally shifted, threw the chain across the granny ring. Worst of all the problem seemed to be intermittant. I attributed the problem to poor finish or some kind of burr on one of the die cast parts. I solved my problem by installing a chain watcher which, as you have said, won't work for you.

I'm wondering if a different front derailleur, even a different 105 front derailleur, might solve your problem.

[rlong]

Thanks guys. My shifting methods might be partly to blame, as suggested, because I do wait until I am in the top three cogs before shifting down to the granny. However, the top three are the only ones I can use with the granny before I get a lot of chain grinding in front. I will try another LBS with a mechanic I know to be more talented.

[rlong]

Bummer! As it turns out, the dropouts are tweaked and chain alignment is off. Waiting to hear from Trek about a new frame!

[rlong]

Bummer! As it turns out, the dropouts are tweaked and chain alignment is off. Waiting to hear from Trek about a new frame!
My new bike is on the way:) I guess they were familiar with the problem at Trek and shipped me a new one as soon as it was painted. Should arrive tomorrow, or the next day. I love running, but with the tandem down and my Pilot out as well, hmmmm. I'm suffering bike withdrawals. I don't know how you all survive where it snows a lot.