Bicycle Mechanics - wheel question....

I recently picked up and old 10 speed mountain bike, and I was wondering if I can swap the rear 5 speed wheel for one with an 8 speed cassette leaving the front cranks and double chinrings? I will be swapping the short cage derailier for a long cage. Will this work without any major problems?..I have also already checked and the frame spacing is fine for it... Thanks for any input...

5 speed is a freewheel. And assuming it's not uniglide the max you should try sticking on their is a 7 speed freewheel. Even though you will most likely need to space out the drive side for the small cogs to clear the frame.

8 speed freewheels are available but you risk axle breakage much more than the 5/6/7 in addition to availability problems in real bike shops. This weakness will be multiplied

a) the heavier you are
b) the rougher you ride the bike

I am swapping the entire wheel not just the cassette. I have another set of wheels from another bike that I was wanting to use without having to swap out BB and cranks..

mostly I am worried about chainlines causing skipping

mostly I am worried about chainlines causing skipping

I'm thinking brake alignment is more likely to be a problem.

I have already test fit the wheels and the breaks work fine with the wheels....I guess I will just try it and see