Shifting problems - what to do next ?

[DaveReading]

I've been having intermittent shifting problems ever since my RD cable worked loose a few weeks ago and the STI shifter ate half an inch of loose cable. It took an hour of careful persuading to extricate the cable and nipple, which I thought I'd managed without any damage to the shifter. Changes had been fine previously.

Now, I can go for a ride where everything shifts perfectly, followed by a ride where changes from a smaller to larger cog on the cassette are extremely iffy - I often have to move up a couple of cogs and then back down one. Shifting in the other direction, from a larger to smaller cog, never exhibits any problem.

I've tried all the usual strategies, reindexed, replaced the chain, cassette and cabling, but to no avail. I even splashed out on a hanger alignment tool, so it's not that.

The possibilities I'm left with are invisible damage to the shifter and/or a problem with the RD itself. While adjusting the latter, I noticed a bit of play in both the parallelogram pivots and the cage pivot. There is also a bit of sideways float in the jockey wheels, but I think that's supposed to be the case.

So my dilemma is whether to replace the RD and/or the shifter, and if so, which one first - but I'd have thought that a problem with either of those would make its presence felt all the time, not just intermittently.

Advice welcomed.

 

[wisdom]

What sort of mileage is on it and what make/model is your rear mech.
TBH I have never worn one out yet and I do a lot of miles in all weather's.

 

[mrandmrspoves]

A lot of possibilities but my first point to check would be that you fixed the cable to the derailleur correctly. The attachment is often ambiguous but if the cable is not clamped exactly right it could cause the issues you are experiencing so worth checking on-line diagram to be sure.

 

[wisdom]

Im thinking along the same lines.Add cable tension to the mix.

 

[DaveReading]

Thanks for the responses.

The RD is an 8-speed Shimano Acera (triple chainwheel), probably has about 6,000 miles on it. I can't swear that the play I described is any more than when it was new, so that may be a red herring.

Re the cable attachment to the RD, I'll check that as obviously it would have been disturbed when I replaced the cable.

Re cable tension (i.e. indexing), I'm assuming that's OK since shifting works fine some of the time ...

 

[Racing roadkill]

It sounds like you have a snag on the cable somewhere. Did you replace the outer as well as the inner? You may find it helps to do so, if you didn’t.

 

[DaveReading]

Yes, both inner and outer are new.

 

[Levo-Lon]

Have you lubed the shifter recently?
It may just be dust and grit ,give it a wash out with a squirt of aerosol lube like 3 in 1
Try that and see if it sorts it.

I think you've done all the other things so i think its just muck in the gubbins

 

[DaveReading]

Thanks, I did squirt some GT85 into the shifter when I changed the cable, but I guess more can't do any harm.

 

[Tail End Charlie]

When you replaced the outer did you cut it to length yourself? Sometimes this slightly squashes the casing which can lead to problems you describe (top tip, when cutting the outer have an old inner in which you also cut). Also the cut ends must be very flush, I spend time with a dremel tidying them up, some shifters are very temperamental about this.
As others have said, flush with GT85 or WD 40 or similar and I grease the new cable as well.

 

[wonderloaf]

This is a bit unlikely but I once had a stone lodged in the RD which caused shifting problems.

 

[DaveReading]

Thanks, that's interesting.

Yes, I did most of the above, cutting the outer with a spare bit of inner inside using my newly-acquired cable cutters (whenever I splash out on a new tool, I look at my latest car servicing invoice to make me feel better )

I'm pretty sure I checked that the ends of the outers are properly round, but I can't swear that they are 100% square - I'll take the ferrules off and if necessary attack the outer ends with a file.

Incidentally, I've just been reading on another forum about the trick with plastic/nylon ferrules of softening them up in hot water to make it easier to be sure that you've pushed the outer in as far as it will go.