i have a 2004 Giant Yukon that has a Shimano Altus Front derailleur using a 34.9mm bottom bracket mount.

I purchased a Deore front d. off ebay for really cheap and it uses a 34.9 clamp mount, top or bottom pull.

I bring it to my lbs and they said that it woudn't work since my bike takes a bottom bracket mount and the deore f d. is for 9 speeds.

I didn't ask in detail why it didn't fit. since i was in a hurry..........

But why can't i just replace the bottom bracket and use the clamp mount?

Also i read on here that i can use a 9 speed front or rear derailleur on my 8 speed with out problems

So can someone explain this to me. ....sorry for the noob question