Bicycle Mechanics - six speed cassette, 8 speed mech

hello!
i'm rebuilding my gf's bike with components from my old bike.
anyway i'm guessing that a 9 speed cassette won't fit on the current wheel, so i'm going to leave it as 6.

my question is this,
will an 8 speed xt mech work with a six speed cassette

Yes, it will. "X-Speed" on derailers is nothing more than marketing buzz. The derailer doesn't care how many speeds you have. Your shifters need to match your cassette, that's it.

thought so! thanks. :)

Yes, it will. "X-Speed" on derailers is nothing more than marketing buzz. The derailer doesn't care how many speeds you have. Your shifters need to match your cassette, that's it.

In this case it should work, but it's not quite as simple as "that's it".
For index shifting the throw ratio needs to be compatible, an 8-speed D-A would not be, a Campy would not be.

Here's the specifics:
All Shimano rear deraillers built since the advent of indexed shifting have the same cable-pull ratio and are thus compatible, excepting pre-9-speed Dura-Ace. So you could use a 105 rear derailler that originally shipped with 6-speed freewheel and down-tube shifters with 10-speed Dura-Ace STI-shifted drivetrain.

I'm not sure that Campy is cross-compatible like that.
Also, Shimano has and has had different standards for front derailler cable-pull. Currently, road front deraillers (including the triples) are not compatible with mountain bike shifters, and vice versa.

it's ok, i've sorted it. and thanks for your input
i have six speed index shifters, bolted it all on and it's all running sweetly.


http://img411.imageshack.us/img411/8069/dsc00054mf5.th.jpg (http://img411.imageshack.us/my.php?image=dsc00054mf5.jpg)

http://img411.imageshack.us/img411/1450/dsc00055nq5.th.jpg (http://img411.imageshack.us/my.php?image=dsc00055nq5.jpg)

http://img411.imageshack.us/img411/917/dsc00056in2.th.jpg (http://img411.imageshack.us/my.php?image=dsc00056in2.jpg)


http://img411.imageshack.us/img411/6960/dsc00057eo1.th.jpg (http://img411.imageshack.us/my.php?image=dsc00057eo1.jpg)

pimping my missus' ride! :D

Wow, those parts are way, way nicer that this bike deserves. But oh well - they should work.
Your front derailler seems to be mounted way too high on the seat tube - it should be closer to the chainrings than it is.
Incidentally, I ran the same rear derailler (labeled 8-speed) with 9-speed drivetrain on my road bike for awhile. It worked great.
http://www.unc.edu/~cupery/pics/bikes/Raleigh_aluminum/IMG_7713--rear_der_cluster.jpg

i know they're too good for the bike, but they're oof my old bike and were just sitting in a box, so i thought i'd do up laura's bike, pimp her ride.
i used to use the mech on my old nine speed, i guess i was more concerned with whether the chain for a six speed would run through it ok.
the front is high, lower than the one i took off though, but either way, i can't get it any further down because of lack of clearance on the chain stays. it shifts fine though :D

your mech looks in damn good condition!!!

the front is high, lower than the one i took off though, but either way, i can't get it any further down because of lack of clearance on the chain stays. it shifts fine though :D
your mech looks in damn good condition!!!
Okay, I see in the picture how you can't get it any lower. That's too bad.
My rear mech in the linked photo has been used for 11 years but never crashed. And it's been on a road bike. Thousands of miles of riding won't wear out a derailler visually :)