Bicycle Mechanics - Unwanted Shifting Problem

I havent ridden all summer, which means i have very few miles on my bike (less then 500) in the year or so i have had it, and everything seems to be working fine. Until a hit a hill. I have a double-chain-ring, dura-ace components. For some reason, when a lot of pressure gets put on the chain (even when in easiest gear) going up hill, my gears shift on me. They make a popping noise i suppose, and i make a half-spin before the chain catches again. Pretty scary thing as it is unexpected and i am crawling uphill...it happens 2 - 3 times everytime i go uphill. Some shifts are worse then others. At first i thought maybe two of the chain-links were locked up, but after checking each one and wiggling each chain-link, this is not the case. Anyone have any idea what might be causing this?

Did you measure the chain? How mamy miles on it? On the cassette? On the RD cable?

Loose der.hanger maybe? Or could it be flexing enough (you say it's only when the chain is under a lot of pressure) to possibly cause it to shift (unlikely, but thought I'd mention it anyway). Crank arms, cogs, and btm.bracket tightened?

Well, i got the bike new. There is very likely less then about 500-600 miles on it. Got it early 2005 i think. Put 200 miles on it in April, and close to 100 miles in the past month. (crappy weather for past 3 weeks here) so there really shouldnt be any *stretch* to it. I've put 3,000 miles on one chain over the course of 4 months and it didnt have any problems (different bike). Not sure about all that other stuff - i personally havent touched the bike since i got it (dont know enough about mechanics to feel safe enough to do anything with it)....

Sure it ain't a case of cable stretch? Check the shift cable tension. Happens a lot with bikes without too many miles.

did you take it in for a tune-up after you had been riding it for a bit? Not that I know a lot about bikes or anything, but the LBS you got it from could likely help you out on that if you dont feel confident trying to fix it yourself.

if everything else checks out, it must be the chain. these 10 speed chains are a pain in the butt. I think the shimano and campy chains use a special pin when they are installed. A friend installed a 10 speed da chain and it would shift on its own...he took it into a shop and they said that the pin was installed from the wrong side. I had never heard this before, but its been shifting fine after they re-installed the chain. I think 10 speed is stuff is good for short mileage if you're over 150 pounds in hilly areas and very short mileage if you're over 150. I'm in the san francisco bay area, so every ride is involves 1,000 feet of vertical gain...I'll stay with 9 speed.

Sheldon Brown's website has an article on ghost shifting, caused by combination of frame flex and friction, where the shift cable passes under the bottom bracket.

Well my bike is a Titantium Merlin (hence my handle)...i was under the impression that the frame doesnt flex a whole lot compared to Carbon Fiber frames etc? Could be wrong. Gonna head out on a ride today (4PM EST) after classes and will try and tackle a hill. I'll better describe what happens. Some hills it is fine on though...the steeper they are, the more likely it is to change. For instance, theres a gradual 3 mile hill where it is fine (6 - 8% Grade i believe) while theres a 150 YD Long, but 12%+ Grade hill where it does shift. Perhaps theres a certaint amount of pressure/stress it can take before it starts shifting?

This sounds like a typical case of cable stretch. Try a counter-clockwise turn on the barrel adjustor.

Al

Which one is the barrel adjustor?

Also, my chain looks pretty filthy (all black etc) compared to a lot of the pics i see on BF. I got a chain cleaner - whats a good lube to put on after i clean it?

Which one is the barrel adjustor?
There are two barel adjusters for the rear derailleur. One is mounted on the derailleur itself right where the cable housing enters. The second is mounted on the right side of the headtube. You can adjust the rd's cable tension with either one.