Brake backing plate replacement

[P-hat]

Anyone replace the brake backing plates (weather shields) on the rear brakes of a 2000 Yukon XL? If so, am I looking at a difficult/expensive job?
After investigating an annoying squeal, I noticed the backing plates are rusted (bubbling and falling apart). I think this is the cause of the squeal.
What is the purpose of the backing plates? Shield the elements?
Thanks in advance.
Paul

[turbojimmy]

It's normal to have some rust and flaking on the outside of the backing plate. Unless they're really falling apart (i.e., there are actually holes rusted through them) they probably don't need replaced. They are not likely the cause of your squeal, either.

But to answer your question, their purpose is to provide a mounting point for the wheel cylinder and brake shoes. They're more than just a weather cover, they're an integral part of the braking system. To replace them you have to remove the axles, wheel cylinders and brake shoes. It's not a terribly complex job but it's messy (you need to drain the differential fluid) and time consuming. The brakes will need bled afterward, too.

If the backing plate(s) really do need replaced you're probably better off leaving it to a professional. The manual shows 3.5 hours to do both sides and bleed the brakes.

Jim