Unreliable Shifting

bigmonka

In the last few weeks my bike has gone from doing great gear shifts to being unreliable going either up or down the rear gears (its a 1x8 Shimano Acera)

I'm guessing its not a cable tension issue if it's having difficulty moving in either direction, so what is it most likely to be? Could it be the spring on the derailleur? Or one of the pivots not moving properly? Or would worn jockey wheels cause this sort of thing? The bike's done ~8000 miles and had new chain and cassette about 1000miles ago - my chain wear tool shows the chain is ok still.

Thanks for the help!

Ouija

Sounds like typical cable binding to me. Probably time to replace inners and outers. Especially any looped sections coming off the back of the frame into the derailleur as this is usually where friction prevents shifts at the shifters fully reaching the derailleur.

If the spring on your derailleur was going, you'd experience poor shifts going down the cassette to smaller rings, not going up (cable tension pulls it up but spring tension is responsible for moving it back down)

Over worn, wobbly, jockey wheels can cause problems too. But not the ones your describing (typically you can get all the shifts in one direction working perfectly but suffer from shifts "lagging" behind in the opposite direction).

I'd try simply replacing inners and at least the last section of the outer cable.

bigmonka

Thanks a lot for the reply - I'm not surprised that the cables might need replacing, they are getting pretty old. I may even do the brake cables too whilst I'm at it as the exposed bits of cable at the ends are starting to look a bit corroded.

Time for an online shopping trip for cables!

Ouija

Get teflon coated cables if you can. Tend to rust less and produce less friction. Black coated SRAM cables tend to be pretty good to.

bigmonka

Great, thanks, I'll have a look.

Ouija

Many years ago i replaced the curved bit of cable that is required with cheap Shimano derailleurs with a Avid rollermajig to turn it into more of a direct pull system (all SRAM and high end Shimanos use direct pull to get better shifting with less cable friction). They don't make them anymore Rose bikes do something a little similar, called the WCW Easy Roller......





My main commuter still as the Avid rollermajig on it and doesn't seem to require new cables after over 40,000 miles of all year round use. Nothing did as much to improve shifting. Certainly suffered lots of bad shifts before the change and had to replace cables after every winter. Most of my high end bikes have direct pull stuff on them and don't require this but my commuter gets cheap derailleurs, cassettes and chains (Shimano Alivio and Deore qualify as this) on them and it was a common problem i faced year in, year out with that setup. So contemplate losing the loop, having to replace cables every year or two or upgrade to something better.

The Rookie

Teflon doesn't stop it rusting, stainless or galvanising (cheaper and not as good) does....Teflon is to help make it run easier by reducing friction.

I'd be tempted to just reindex it first, checking all the settings and that the mech is free to move as it should.

Initialised

I'm with the rookie on this, keep it clean and re-index every month or two if it goes out.