[young gun]

I am having a weird problem. My bikes back brakes work fine but then randomly it will make a kind of grinding seized noise when ive pushed down the kever and then go back to normal as soon as I have released it?! While this is happening the brakes won't work as well. It's happened to me 3 times now while out riding but will literally last a second or so and then be back to normal? Any ideas?

[High On Octane]

Try disassembling the brakes and clean them up real good and relube the moving pivot points.  Sounds like you have gotten a large piece of debris in your brake assembly.
Scottie

[barenekd]

But on reassembly, make sure the brake is setup properly. Reassemble it onto the bike with the wheel, etal, all attached, but with the axle and brake nuts loose. Make sure the chain is adjusted where you want it. Tighten the brake backing plate nut slightly (The big one behind the axle nut) and tighten the brake adjuster nut down to lock the brake and center the shoes. Then tighten the rest of the nuts, the big one first, the axle nut, then the pivot pin nut. Adjust the brake adjuster nut to the point you want the free play. I usually use about an 1/8" of pedal play.
This will insure that both brake linings are against the drum, when applied, for maximum braking. They won't be fantastic, but you should be able to lock up the rear wheel when wanted.
Bare

[young gun]

Thanks for the advice, ill take a look see