I don't know the Focus but I suspect this job is pretty similar and pretty easy for most cars. I found the hardest bit was undoing the brake caliper bolts. They were very tight and there wasn't much room for a breaker bar. Don't let the free caliper hang on the brake hose - tie it up with some wire or string.

If your rear disks include handbrake drums, remember to set the handbrake off.

When the old disks are off clean the hub mating surface so the new ones fit square - you're supposed to check for float with a dial-gauge but I improvised. Make sure the caliper pins slide freely, put copper grease on the sliding surface of the new pad but don't get any on the friction surface or disk.

CAN ANYONE TELL ME HOW HARD IS IT TO CHANGE THE REAR DISCS & PADS ON MY 02 FOCUS ESTATE

ALSO THE SPRING HAS SNAPPED ON THE FRONT DRIVERS SIDE SUSPENSION CAN I JUST CHANGE THAT OR IS IT A COMPLETE UNIT + DO I NEED TO CHANGE THE OTHER SIDE ASWELL

For your own safety change both springs and preferably both shockabsorbers but make sure the "cups" on the macpherson struts are not corroded as well. you can buy aftermarket struts and springs and shocks, try europarts or get a quote from national tyres for all the work. PLEASE PLEASE make sure the spring holders are good, your life depends on it. Good luck!