dja1

The high/low limit screws are correctly set. All shifts can physically be made, and the derailleur cannot travel beyond the top/bottom of the cassette. I can't feel any drag in the system either, the derailleur spring is firm and returns the derailleur in a single motion.
Chain is around 150 miles old, casette, <50. I think this problem was beginning to manifest even before replacement.

I can't get the rear derailleur to index accurately, and it end up out one way or the other as I attempt to index further. It is worse depending on cross chaining, but I understand that it should still be making all the shifts smoothly, across the full range, in both chainrings regardless of the fact that you shouldn't cross-chain, correct?

5-6k miles on the cables in fair weather. I try not to let this bike see rain or winter.

n.b. I did take a knock on the bike 100-150 miles before I started noticing shifting problems, and they have followed me with my new chain and cassette. Yes the derailleur took a knock; it is scratched and missing the B axle cover cap. I know a bent hanger may be a possibility, but would I not have noticed this earlier (one would assume falling onto the drive side would exert energy inwards on the mech; chain ends up in the spokes, or has visible excess travel when on the low limit?)

edit; just looked under hoods in the higher gear. Can't tell if the cable is frayed or if it is just the polymer coating is rubbing away a bit. Shimano said the latter is normal I think.

grizzly59

I would check the derailer for alignment, look for a bent hanger. I would also take out the chain pulley closest to the cogs in the rear derailer. Clean, grease, reassemble. It should slide back and forth a bit on the axle. Might as well do the other pulley.

Bigbus

I had that issue on an old MTB and it turned out to be the front DR was not aligned with the frame and it pulled the chain to one side or the other causing the RD not to index correctly no matter what I did. After realigning the front DR the rear came into alignment and I was able to index it again. I was sure that it had to do with the hanger before discovering the true culprit. And yes, it happened shortly after a good knock on the ground. Good luck

dja1

I did actually have the pulley wheels off earlier to clean the inside of the cage as it has gotten quite dirty. I cleaned the wheels externally and wiped excess muck off both sides of the metal covers, but left the bearings & their seals undisturbed. They don't feel or sound gritty. Do they need reassembling?

Iride01 

Assuming the 5 - 6 k is 5000 to 6000 miles and not 5 - 6 kilometers <grin>, then check that the cable isn't frayed up in the shifter. Especially if these are STI's, I don't know if it's an issue for other shifters. My son's Tiagra 4700 had indexing issue when going from the bigger cogs to the smaller cogs and his cable was frayed in the shifter after only 4000 miles.

dja1

the polymer coating has stripped a little, but the cable remains intact and appears to operate smoothly inside the hood assembly.

dja1

Sadly I can't see the front mech throwing it out, the height looks to be spot on and I can trim to account for cross chaining otherwise this would be a nice straight forward fix for me I think.


a question regarding the hanger alignment tools if anyone knows... to be totally accurate, do they rely on referencing a rim which must be free of even the slightest of buckles?

Iride01 

The other time I had indexing issues that weren't readily apparent and seemed sort of random, I eventually found that the shifter cable was sawing itself into the BB shell of my bike. This was an older bike that just ran the cable on the bare bb shell and just had a few lumps of brazed material for a guide.

Roadies_Rok

I suggest you take a look at the rear wheel. If the rear wheel has a freehub and a cassette make sure the bearings on the freehub (drive) side are in good shape. If they are not a lot of times you will get an up and down oscillating in the cassette which can mess up the shifting. You may have to remove the freehub body to do this which can be a PITA but it could be worth it.

Drew Eckhardt 

I wear out rear shift cables in 2000 miles and my housing goes high friction in 4000. I wouldn't bet on no frayed strands in the shifter.

masi61

I would replace that cable with a non-polymer coated. The stripping off coating will hang up inside the housing. I use the Jagwire burnished stainless inner wires.

dja1

I am sure a replacement of the rear gear mech cable would not hurt. I have been tempted to do away with the dura ace cables and go for the standard shimano ones as mentioned in the your comment.

masi61

The Park DAG-1 that I use has a dowel pin that you are supposed to rotate around to different parts of the wheel. If you have a rim seam that stands proud don't use this as a reference point on your rim. Crashing the bike (or banging it accidentally against some object) on the drive side might not reveal itself as catastrophic initially but the poor shifting that results does indeed usually come from a bent derailleur hanger.

Does your frame use a removable derailleur hanger? If you have a spare you could swap it out and see it shifting improves. Make sure the bolt that holds the hanger on is secure BTW. But to know for sure, you really should check it yourself with a derailleur hanger alignment gauge or better yet take it to the bike shop and pay the $ to have them do what they are trained to do.

dja1

Ok. I have been toying with the idea of getting a new hanger, replacements are available at a cost of £25, but from researching hanger damage & repair, I believe it isn't uncommon to have to align new hangers to your frame so this might be something for the LBS to look at, as I'm not sure I want to spend the money on that tool right now.

I could swear though that I had a couple of rides after the crash and shifting was ok, but I can't rule it out

dsbrantjr

Or shreds of that (IMO bad idea) polymer coating jamming things up. .

Crankycrank

As mentioned that shedding polymer can gunk up your shifter. At least push the head of the cable out from the shifter for 1 1/2" and scrape off the polymer coating. Better yet just replace the cable as it is getting in the risky zone mileage wise. Also another vote for checking the hanger alignment since the OP mentioned troubles started after the derailleur got bumped and before replacing chain and cassette.

dsbrantjr

If you decide to replace your inner wire, just use die-drawn stainless, it has virtually the same coefficient of friction against the PTFE housing liner as the coated stuff, doesn't shed and is easier to clamp securely.

masi61

If you are on a budget, I think it is possible to make a functional derailleur alignment device on the cheap. More of a coarse adjusting tool. So, for example if while visualizing the derailleur pulleys from the rear of the bike you are able to decipher that they are not "co-planar" with the cassette and the crankset (chainrings) you can put an oversized allen wrench into the bolt that holds the rear derailleur to the hanger and try to bend the hanger in the opposite direction that it appears to be impinging the wrong way. Ironically, doing this procedure correctly most likely requires experience with the proper derailleur alignment gauge in the first place. So take this advice with a grain of salt, LoL.

dja1

I might bite the bullet and go for it knowing that it may be useful in the future. I just see some folded steel and wonder how the shops can charge £62 for the thing. I bet it would be easy to make one of those yourself with some metal, a welder and set square.

There is an alternative which saves £20, but I wonder about quality and play in tool: https://www.chainreactioncycles.com/...RoCe88QAvD_BwE

dsbrantjr

[QUOTE=dja1;21424081]I might bite the bullet and go for it knowing that it may be useful in the future. I just see some folded steel and wonder how the shops can charge £62 for the thing. I bet it would be easy to make one of those yourself with some metal, a welder and set square.

There is an alternative which saves £20, but I wonder about quality and play in tool: /QUOTE]

Reviews look good, apparently there is a screw adjustment to take out any play.

RGMN

You use the same spot on the rim for all the measurements so the wheel trueness doesn't affect the measurement. Usually you use the valve stem as it is an easy point to repeatably find, but I've used a rim seam as the reference point just because I could find it by feel.

grizzly59

You should be able to check / align your hanger pretty close by eyeball. You can turn it upside down and look vs plane of the cogs. Highly skilled and trained help could turn crank and shift gears while you watch derailer. Bicycle .NE. SR-71

grizzly59

This is all excellent advice. Compressed air helps clean out shifters; oil, blow, oil, etc. Die-drawn stainless is the way to go. The one thing I won't take apart is a brifter.

dja1

QUICK UPDATE.
so where is what I found inside the shifters. As you can see it is quite frayed and there was a build up of polymer around each ferrule.https://imgur.com/a/RhepKDp


How risky is it reusing the outers?

Iride01 

Depends on how much you hate going through the procedures for replacing and getting the cable set correctly in the hold fast on the DR's. I'd just replace the cable and see if there is an issue. If there is, then I'd replace cable and housings. But I just use the standard Shimano cable sets.

This being the higher performance cable and housings, perhaps it should be replaced together. Higher performance doesn't mean longer life in many products. It just means it gives the ultimate in function.