The pin is what retains the caliper and allows it to slide back and forth. It should move with some small effort when it is installed - to check, you will want to compress the piston using a large G-clamp with the caliper in place. Once the piston is fully compressed, you can try to slide the caliper back and forth on the pins.

There should be some very slight "wiggle" on the pins as well - that's the same clearance that allows the caliper to float.

The rubber "bushing" is more of a boot than a bushing, and it's there (mostly theoretically) to keep dust and crud off of the pin and keep it from sticking. Doesn't always work - which is why I use graphite to lube instead. Takes care of that (see my comment on grease and brake dust.)

Often, the rubber boot is also a bushing, which provides a replaceable wear surface for the pin to ride on. This (theoretically, again) prevents having to replace the caliper when the hole gets worn - simply replace the rubber bushing instead. I sometimes think about the idea of a slight redesign to put in a bronze bushing instead - since it wears better than rubber. I just need to figure out how to retain it.

And, if you think that's bad, I've seen (mostly on Fords) applications where the caliper is simply retained by spring rails - they both retain the caliper and provide one of the sliding surfaces for it. There's nowhere near as much tension on one of those spring rails as there is on a decent roll pin, even, so I just don't trust those things. I'd rather have a pin with screw threads anyhow...

 

Don't feel too bad, I've often had a hard time understanding some engineers and their wacked out ideas when something less than half as complicated will do the job twice as well.

But then they have to justify all the money spent on those chunks of wallpaper. . . . .

I see NAPA is offering specially compounded pads for inner and outer pads to compensate for the fact the little rubbers don't do the job perfectly.

Budd