Gear change problems

[Chris S]

I have an older Raleigh MTB with 15-speed Shimano gears.

1st, 2nd an 5th gear changes are OK.

I can change down to 3rd and 4th gear if I move the thumb shifter half way past the notch and let it flick back, otherwise the chain just stays on the higher cog and rattles.

More importantly, I can't change up to 4th gear. The chain just stays on the third cog and rattles. I can change directly from 3rd to 5th without any problems.

Does anybody have any idea what might be causing this please?

 

[videoman]

Hi, are the gears indexed? I would try adjusting the gear outer cable usually at the gear change mechanism and apply a little more tension to see if this resolves the problem.

 

[Globalti]

If it's an old bike the cables will be well and truly past their best. If you feel competent to do it, buy a couple of metres of cable outer, two new inners and a cable cutter and fit new all round. Alternatively get your LBS to cut the right lengths for you. Don't forget to get the two little end caps and some plastic ferrules for the outers.

You'll be amazed at what a deterioration in shifting performance you've become accustomed to.

That cable outer that curves round to the rear derailleur needs changing every six months to maintain the best performance.

 

[Chris S]

RE: "are the gears indexed" - Yes, I'll try readjustment first.

Would bad adjustment or a worn cable just affect some of the gears? 1st, 2nd and 5th seem to be working perfectly.

 

[Globalti]

Yes. Worn or claggy cables cause all kinds of strange effects.