i have a diamond back bmx bike.
currently i was thinking about changing out the hubs of my rims in front to quick release hubs so i could mount the bike on my thule fork mount rack.

can this be done?
will this work for mountain bikes also?

The short answer: no

The long and complicated and ugly answer: yes

The axles are different diameters, but just barely. Assuming loose-ball hubs (if your hubs use sealed cartridge bearings you're going to have a MUCH tougher time), you can *get away with* a 9mm q/r axle in a hub designed for 9.5mm (3/8") axles at the possible expense of a little smoothness and longevity. It will require purchasing a new axle, new cones, bearings, possibly retrofitting seals and dustcaps. I myself have converted a 9mm q/r hub to 3/8" BMX on my fixed gear and it works fine, but it was a real pain in the ass and required a little bit of creativity.

Sounds like a bad idea, just put your bike your back seat.

Haha.

Sounds like a bad idea, just put your bike your back seat.

Haha.thats what i'd do

samsongee be careful i have a diamondback and everyone in here says diamondbacks are crappy

yep