Trigger shifter weirdness

[mcshroom]

I've not met this one before, and I would appreciate any advice people have.

I've just been out on my mountain bike (an 8yo Voodoo Bantu) and the left hand trigger shifter was acting strangely. Switching between the inner and middle ring it worked fine, every time, but when I tried to move into the big ring it felt like sometimes there wasn't any resistance at all and it wouldn't shift - though I could do it by reaching under the bars and pushing it much further back than normal. Later on it worked a bit better, but it felt like I needed to pump up the lever a couple times before it would shift up. It's obviously not the case, but to give an idea of how it felt, it was a little like having to pump up pressure in a pneumatic system.

It always shifted eventually, and the shifting of the other two rings suggests that the cable tension is ok. I haven't had a look inside yet. I believe these are Acera shifter pods, but I usually ride on the roads so don't have much experience with flat bar stuff.

 

[Cycleops]

I'd still suspect cable tension.

 

[wisdom]

I'd still suspect cable tension.

I would suggest cable tension as well or it could be a frayed or sticking inner.

 

[raleighnut]

It does take quite a shove to change the front rings on my bikes with trigger shift,

 

[Illaveago]

It's not the ratchet mechanism starting to stick is it ?

 

[Cycleops]

I should try a new cable and grease it. Before installing hold it taught and make sure it's pulling correctly when you operate the shifter. It might be just gunked up as @Illaveago suggests so flush some maintenance spray through it.

 

[Milkfloat]

Same symptoms I had for a year or so. GT85 used to cure it for a while, until one day when it did not, I tried to take it to pieces, found some teeth stripped from a cog, so now run a single chainring up front.

 

[Gravity Aided]

I would check cable tension, and see if there isn't a little spinner on the place where the cable enters the shifter, to see if you can take up any anticipated play there. If not, or if there isn't enough tension then, I would undo the high side of my front derailleur a couple of turns, take up the slack, and see if that doesn't help. I had to do this with my Trek when I saw problems in my pre-season fettling yesterday.