Cassette change

diamondback are not dead

I am currently running a shimano MTB specific 8spd cassette and i am considering changing to a road bike cassette for the smaller ratios will my mech need adjusting for this to work?

the mech is a shimano LX top normal

supersonic

Mechs almost always need adjusting when a new cassette is fitted. You may have to screw in the B adjustment screw, and shorten the chain.