Skipping between cogs 2, 3 and 4

[RichBike]

I took my Trek FX in for its first tune after 2400 miles to the same shop I bought it from. The only problem with the bike before the tune was that the brake pads were almost non-existent (I ride in a hilly area). After $95 and a 10-day wait, I couldn't wait to get out on the road again. Unfortunately I had to cut the ride short as the the bike would not stay in gear if it involved the 2nd through 4th cog; it would shift back and forth under pressure (the more pedal pressure the greater the slippage). Any ideas other than I need to find a new bike shop?

[GeorgeET]

Well first of all you should try to not shift under pressure especially up hill. Not sure if the dereiler skips cogs or chain jumps of them from your description.

I'd first talk to the bike shop and explain the problem , have them readjust it. Dudu happens.

Sometimes a bent dereiller or a worn out shifter will skip gears.

[RichBike]

I'm not shifting under pedal pressure, the bike is doing so because it won't stay on cogs 2-4 while applying pressure. It shifts back and forth with greater pressure equating more frequent 'auto-shifting'

(07-22-2011, 02:07 PM)GeorgeET Wrote:  Well first of all you should try to not shift under pressure especially up hill. Not sure if the dereiler skips cogs or chain jumps of them from your description.

I'd first talk to the bike shop and explain the problem , have them readjust it. Dudu happens.

Sometimes a bent dereiller or a worn out shifter will skip gears.

[RobAR]

Hey Rich. For a $95 dollar bill, I would assume that you had new cables and housing installed? If so, I would do as George advised and take it back to the LBS. This isn't uncommon and I'm sure they will dial it in as needed pro bono. The first ride is quite soon to expect your problem but, that's what the barrels at the shifter and drlr are for. Fine-tuning on-the-fly.
Bikes will also work MUCH better in a repair stand than in the real world. Like the tooth that no longer hurts when you get to the Dentist. Weird.

You may even ask them to let you watch and get advice on some DIY if you catch the mech in a good mood. Beer 15 minutes before closing time might get him motivated! Unless he has a ride planned... timing is critical.

Barring all of that, the only other explanation (I hope not!) is a weekend or compromised frame that is allowing flex at a certain point of torque. One that you like to ride in.
Which FX (ex 7.5) and what year? OEM Rear Drlr?