Front derailleur 9spd vs 10 spd
I wish to upgrade my current FD.Itīs a crappy Shimano Altus with Mega9 logo.I got the same logo on the chainrings.My replacement is an XT 10 sp.The issue is: I only got 8 spd in the back and the XT has a Dyna Sys logo on it.Will it be compatible?It does match the outer ring tooth count.
The issue you'll have is chain rub due to the more narrow cage of the 10 speed front derailler. You could compensate by using a 10 speed chain but you'd be adding needless expense. 9 speed would be slightly better in this regard but still not as good as 8 speed.
Why exactly are you replacing the Altus derailler anyway? While cheap, I've never had an issue with getting one to shift to my satisfaction.
Derailleur spring must have rusted last winter or something so shifting in the front requires quite a bit of force,Iīve broken 3 cables already.The combination I want to use is FD XT M770 10 sp top swing and HG93 9sp chain which Iīve bought already.What if I manage to adjust de FD perfectly, will I still get chain rub?
I've used an Acera group during the past 5 northeast winters and aside from needing new cables and housing and some lube here and there, nothing has needed replacement. If you are breaking shift cables, I can almost guarantee you that you have some other problem than the front derailler. If your front derailler was that stiff, you'd have broken your shifters long ago. More likely, you have a cable/housing routing issue that is causing excess friction possibly bending the cable at too small of a radius and that is causing the breakage.
Try disconnecting the cable and see if you can move the front derailler by hand. If it moves through the full range and always springs back to the inner chainring position, it does not need to be replaced. It will feel stiff but it should not bind. If it does bind, you may just need some lube on the pivots.
Once you've verified that the derailler is operating ok, remove the cable from the shifter and try actuating it. Does it feel just as stiff without a cable in place or does it feel normal? If normal, the problem is the cable and housing between the shifter and front derailler. If your front derailler is a bottom pull, check the cable guide under the bottom bracket. If you haven't replaced the housing, definitely do that along with using new ferrules. Make sure you have enough slack in the housing that the handlebars can be turned fully without pulling the housing tight.
To answer your final question, everyone I've heard talk about their experience using a 8/9 speed chain with a 10 speed front derailler has had the same unsatisfactory result. No amount of tweaking with give you the same noise-free performance that you'll get by using a matching chain and derailler. You are welcome to try it. you won't break anything but you likely will be disappointed. You'll also be disappointed if you go installing new components without first fixing the underlying issue that is causing the excess friction and cable breakage.