Help...When index shifters go bad!!
 

Hi there.. I have searched the forum and many folks have had index issues, but none of the fixes that have worked have been successfull in my case so here goes.
My bike is a 2002 Whyte PRST-1 recently bought on ebay so I have no history of the bike other than my own cycling experience.
Problem. The 9 speed index shifter gives the correct number of clicks and apparent movement of the cable ( off the bike ) but when fitted will stumble on 2 up and the same 2 down shifts. 2-3 and 7-8
The components. Deore XT M770 9 speed shifter
Deore XT M773 DR
CS M953 9 speed cassette
Also new cables inner and outer and new 9 speed chain.
There is no visible damage at all, it's all straight where it's supposed to be.
What I have proven so far.
Without the chain or cable fitted I have got full and free movement to and from both upper and lower limit screws.
With the chain only fitted all gears can be selected whilst moving the rear mech by hand.
The B screw is correctly adjusted as is the length of the chain.
With the cable fitted and no chain, the rear mech does not shift inline with each rear cog as you would expect, there seems to be a couple of "half shifts" if you get what I mean.
There is no issue with cable routing or stiction as I have removed the shifter from the bars, and fitted it via 6 inches of outer directly to the rear deralieur with a bit of old cable therefore completely removing the cable routing arguement. And yet it still wont give me the full 9 gears.
I think I have proven it cannot be anything except the shifter being worn on the two index points that it fails to change correctly at.
Has anyone come accross this before and can confirm my findings.?
I am loathed to throw money at anything without knowing if it will fix the issue as these are ( in my mind at least) quite expensive components and I don't want to start putting crappy components on what is a beautifull bike.
Sorry to have rambled on, but it seemed easier to answer all the questions others have asked in the past before we started.
Kind regards Simon. :crash:

I would seriously doubt that new levers could be responsible for the problem. Much more likely IMO would be the the rear gear hanger is bent, probably in transit, and this would give the problem you describe.


From the rear, sight along and note if the der cage is directly under the engaged sprocket. Sometimes the skew can be seen but in some cases it need the alignment tool to determine this.

Hi there, thanks for the reply.... As of yet no new shifter has been fitted, and I am trying to establish the cause before I do so. Intersesting you mentioned alignment as it all looks fine so I will have to get it checked.
Simon

One other possibility to check... You say you have all new cables. Is it possible that the wrong type of cable housing was used. If a brake type compressable housing was used rather than a derailleur type non-compressable housing, this could be causing or at least contributing to the problem. At certain times, the housing could be compressing just enough to keep the RD from moving fully to the next position via the indexed shift. Just something to check as it's cheap to fix.

I've also experienced issues with Shimano indexed shifters where they get gunked up internally over time. I've had luck with removing the mechanism from the housing, dousing it down with WD-40 and cleaning out the gunk, drying and relubing with a proper lube (Tri-flow in my case) and reassembling. This procedure has cured many shifting issues I haven't been able to nail down to another cause. All it takes is a glob of dirty, gritty old grease to cause the index shifting to skip or not fully engage properly.

Both of these are cheap fixes, and hopefully one or both will correct the problem before you have to go out and spend more on replacement parts.

Thanks.. Correct SIS shimano cables fitted inners and outers and shifter de gunged with de- greaser and re lubed. If I fit an old cable and loop it round a nail, then the shifter seems to work fine and pulls consistently throughout the range it just wont work on the bike !
Simon.

Wear on your chain and cogs could be the culprit... measure your chain.

Brand new 9 speed chain mate.

note that brand new chain combined with old cogs can cause problems

how about the cable clamp on the derailer? correct clamping position is not always intuitive and can cause pull ratio / indexing discrepancies

Ah, you don't mention the cassette.

If you have a new chain on an old cassette, you're often more likely to face drivetrain issues than if both have worn together...

If you replace chains when they're only 1/2 to 2/3 of a percent elongated, you can get two or even three chains' worth of life out of your cassette, but once you've used a longer chain on it for a while, it's damaged goods.

It can sound like a hard sell when you hear this in your LBS, but engine rebuilders know about this sort of stuff; they have to number identical parts as they come off so they can go back on in the same place and orientation to ensure the wear patterns remain matched, or carnage ensues.

For more info, see this thread: http://www.bikeforums.net/bicycle-me...rain-wear.html

Point taken regarding new chain/old cogs and cable clamping. On the rear mech body ( Deore XT M773 ) there is a groove/ indent for the cable to follow and the clamping plate has a tab which sits in it's own recess and only does so when it's correctly orientated.
simon

Again thanks for all the suggestions, but what I think I'm really trying to find out is has anyone experienced an index shifter 'slipping' when under load and not give the full sweep required, even though it gives the correct number of clicks and apparently correct pulls per click ?. As I mentioned in my first post I have tried with the shift cable fitted and no chain on the bike. So with new cables, well routed, everything clean, lubed and straight... Yet I dont get the full sweep and no it's not the limit screws !!

Sounds like a pretty uncommon sort of malady... I'm not sure I buy you're diagnosing it correctly.

See, Shimano shifters work on a sort of ratchet mechanism, so it's hard to envision them slipping. They have a common fault where the lever won't catch on the mechanism to turn it, which is due to one or two little pawls getting gummed up. But the spring that actuates the pawl which holds the mechanism in place is generally much, much stronger and there's pretty much no way gummy grease can stop it doing its job.

But then again, although they all operate off the same principle there's a lot of variation in Shimano shifter design, particularly at the upper end...

OTOH I've fixed dozens of Shimano shifters, road and MTB, and I've never come across the symptom you describe.

Your absolutely right Kimmo it is well strange. I have ridden and maintained my own and my kids bikes for the best part of 40 years and have never needed the resources of a forum before, as with a bit of lateral thinking, most issues can be overcome .... however this one has me beat !!

Sorted !!!! went to my LBS and we tried a new shifter, same problem so it had to be and turned out it was the rear mech. It had quite a bit of lateral play, odd really but all the joints were just a bit sloppy and it all added up to absorbing two of the gear changes. Mech changed, problem fixed Happy Daze.:thumb:

Well there we go.

Thanks for letting us know what it was :)