9spd mech with 8 speed groupset?

[I like Skol]

Damn! I think I have just worked out why my indexing is so sh*te.

Just over 2 years ago I had a catastrophic coming together of the original XT rear mech and wheel on my 8 spd 1994 MTB. As part of the rebuild process I fitted one of THESE and all was well for a very short time. Ever since then I have been continually tweaking the indexing, lubing the cables and even replacing cables as the symptoms were just like sticky cables. In the last couple of months I developed a niggling doubt about the rear mech compatability so just checked and sure enough I have fitted a 9spd mech to my 8 spd system which, correct me if I am wrong, is not compatible?

To be honest I am really hoping this is the problem because I was getting to the point of starting to dislike riding my beloved 1994 GT Zaskar (from a time when they were real American made frames with lifetime warranty) as it was just such hard work to get decent gear changes (overshift a little, drop 2 gears then change back up 1 etc).

Am I on the right track here? If I am the I will bang on a correct spec mech and then this bike is in for the winter of it's life as it is going to be thrashed just like the old days!

 

[I like Skol]

Hmmmmm...... My options for an 8 spd mech look very limited, maybe an Alivio or similar? I will investigate further, any suggestions?

 

[HLaB]

My sirrus an 8sp bike, came fitted with a 9sp tiagra derailleur and that has never let me down.

 

[TheDoctor]

9 speed mechs should work fine on 8 speed. Is the mech hanger bent?

 

[I like Skol]

9 speed mechs should work fine on 8 speed. Is the mech hanger bent?

The hanger was snapped off but I managed to source a quality replacement (not easy on a 15yr old bike) so should be all good but I will eyeball it all tomorrow to rule out any funny business in that department.

I did google the issue at the time (7/8spd compatability with 9 speed) and assured myself that it would all work but in light of the continued problems I wonder if there is an issue, hence the sale of 7/8spd mechs and 9spd listed seperately.

 

[CamPhil]

Cable pull ratio (the amount the mech moves for a given amount of cable pulled) is identical, so 8 & 9 speed mechs are interchangeable, at least within brand.

 

[PpPete]

The hanger was snapped off but I managed to source a quality replacement (not easy on a 15yr old bike) so should be all good but I will eyeball it all tomorrow to rule out any funny business in that department.

As others have said - I see no compatibility issue, but in view of the above I suspect the hanger is somewhat out of alignment. Whatever snapped the original hanger may have very slightly bent the frame around the drop out. You are unlikely to be able see this with the naked eye.

Unfortunately the tool needed to check (and adjust) the alignment is £50 - £60 so for a one-off it may be worth nipping in to the LBS.

 

[mickle]

You might have some issues with running an eight speed chain through a nine speed mech. Because the wider chain limits the amount of sideways that the top floating jockey can do it makes the mech much more sensitive to maladjustment. It's easy to rectify by fitting a nine speed chain next time it's up for replacement or exchanging the jockey wheels (and jockey wheel bolts) for eight speed uns.

 

[I like Skol]

I may have found something? I have confidence in the rear mech alignment but looking on Sheldon Brown's site I see this -

Note, also that most rear derailers do not care how many gears you have. You do not need to have a so-called "10-speed" derailer to use a 10-speed cassette. This is true of all Shimano derailers with the exception of 1996 and earlier (pre-9-speed) Dura-Ace units, and "Shadow" series derailers, which work only with XTR 10-speed shifters.

As I have fitted a 'SHADOW' SLX mech perhaps this is the answer?

 

[mickle]

I may have found something? I have confidence in the rear mech alignment but looking on Sheldon Brown's site I see this -

Note, also that most rear derailers do not care how many gears you have. You do not need to have a so-called "10-speed" derailer to use a 10-speed cassette. This is true of all Shimano derailers with the exception of 1996 and earlier (pre-9-speed) Dura-Ace units, and "Shadow" series derailers, which work only with XTR 10-speed shifters.

As I have fitted a 'SHADOW' SLX mech perhaps this is the answer?

Yeahbut when did he write it? Sheldon is becoming increasingly out of date. I'm pretty sure that was written when Shadow was only available in 10spd. If you had a ten speed shifter driving a nine speed mech it wouldn't work in more than one or two gears.

 

[I like Skol]

Right! I really think I have got this nailed now. I removed the rear mech and checked the hanger alignment and it is spot on in the vertical and horizontal plane. While I was buggering about with the cables and reseting the indexing I found that the adjuster on the 16yr old XT shifter has threaded. The thread seems to have just worn away which is odd because any trim adjustments have always been done with the shifter set to the smallest sprocket so there is no cable tension. This would explain the continual poor shifting.

To remedy this I have limited options as 8sp stuff is so old school. I have ordered these -www.parker-international.co.uk/5654/Shimano-Alivio-M410-8-Speed-Rapidfire-STI-Levers.html

Gear change should be as good as new once these are fitted.

 

[fossyant]

I sourced a A1 condition 8 speed XT rear mech off ebay for my early 90's MTB as a replacement.

 

[I like Skol]

Was this in the last week or two? I watched one go for about £13 and was tempted myself but in my case I am now pretty sure it is the shifters that are the problem, not the mech. I will find out this week.