i'm getting a set of old 7 speed acera on mavic wheels and i'm going to fit an 8 speed freehub.
I'm going to change the spindle but will i need to dish the wheels?
If i do,could i just loosen spokes on one side and tighten spokes on drive side?
Thanks for any help you can give me.
Yeah, you'll need to redish your wheel. If you go exactly the same amount, about 1/2 turn at a time, tightening the drive side spokes and untightening the left side spokes it will have a minimal, if any, effect on your wheel's trueness and overall tension.
Actually, you probably don't have to change the axle either. Assuming your hubs are 126 mm and have a 137 mm axle, they have the usual 5.5 mm of axle sticking out of each locknut. If you widen them to 130 mm, and recenter the axle, you still have 3.5 mm of axle at each end and, with a good quick release skewer, that's plenty. Sheldon Brown always said changing the axle wasn't needed for this OLD change.
BTW, are your hubs 130 or 135 mm already? If so, you need no axle change at all.