I need to replace my disc brake pads on my Shimano XT brakes. This seems like a pretty straight forward procedure, and I have all the tools needed except for the pad spacer. Do I need this to install the new pads correctly, and if I do, is there something else I can use?
The pad spacer is intended to prevent you from accidentally closing the brake without the rotor in place. It is not required, for any part of the adjustment or installation process, as long as you do not need to bleed the brakes, and as long as you refrain from squeezing the lever without a wheel in place.
If you do need to bleed the brake, it is convenient, but not required.
If you're worried you could substitute pretty much anything clean, solid and non-metallic. The spacers are just wedges of plastic, they're not that magic. A small strip of plywood does the job, that's what I used the first time I changed my pads when I was worried about the dire warnings I'd read.
But I've changed dozens of pads since then and don't bother any more.
The process of changing pads is pretty straightforward, you take the old ones off, and shove the new ones straight in. Just don't muck around while the pads are out and don't squeeze the levers.