Gear changer sometimes "misses"

[benb]

OK, this is a bit odd.
On my MTB, the right thumb gear changer, which moves the gear to the larger cogs on the cassette sometimes misses. That is, it moves all the way to the front of its travel without moving the rear mech.

I'm guessing there is a cam or something similar within the gear changer, and this is occasionally not picking up the bit that moves the mech.

I would say it happens between 1 in 10-20 changes, and seems to be more common just after a gear change the other way.

Does anyone have the first idea what I'm on about and how to fix it?

 

[fossyant]

Can you lube the inside of the mechanism - you'll need a light oil or WD40. Sounds like the lever isn't catching the ratchet. Don't pull it to bits though - you'll regret it.

 

[Blue Hills]

I get this rather a lot on the cheapish and rather old Shimano gear changer on my steel hybrid. I should really change it I suppose, but I usually find that spraying in some GT85 helps a lot. As fossyant says, tempting as it might be, I gather it's a bad idea to try to take it apart to figure out what's happening inside.

 

[benb]

Hmm, well it's brand new, which is annoying.
How would I spray some oil in without taking it to bits?

 

[Blue Hills]

If the bike is brand-new, I'd take it to the bike shop.

If not - you are asking a fairly non-mechanical person here, but I usually find that there's a small hole/crevice somewhere - spray a load of LIGHT oil (such as GT85) into it and then work the gear change a lot - preferably with the bike on a stand of some sort or with the rear wheel off the ground. It works for me and a pal as well. But don't take it apart.

 

[rusty bearing]

Aye GT85 sprayed liberally into any opening does work, I wouldn't recommend taking it apart unless you have a lot of patience, lots of springs and small cams etc. I rebuilt a Sram shifter for one reason or another, took a bit of tongue chewing and lots of tea breaks!