Brake caliper separation after use?

[Tamarack]

This is a pretty basic question, but brake work is new to me.

I just installed a new MC on my 84 xs400, using the rest of my old brake assembly. It works, but when I apply the brakes they stay (mostly) engaged. I think that the piston is backing off, but the brake pads stay tight against the rotor. I can turn the wheel with force, but it's tight. My first thought is that I forgot some sort of spring, which is what separates the pads on the hydraulic brakes on my mountain bike. However, the parts diagram show no such thing, so it must work differently.
http://www.partzilla.com/parts/search/Yamaha/Motorcycle/1983/XS400RK/FRONT+BRAKE+CALIPER/parts.html

My question is how are the pads supposed to move apart after the piston recedes back into the housing? Is it just the banging of the rotor that pushes them back? Or is there supposed to be some other physical mechanism to push the movable pad back? Do the brake pads just need to be greased along the bolt that holds them in, which they slide up and down? Are they supposed to 100% clear the rotor after letting go of the brake lever, or stay loosely against the rotor?

If anyone can explain how this system is supposed to work I would be grateful.

 

[Under Dog]

Quick and dirty answer: it's the banging of the rotor that pushes them back (sort of).

I think it's partly the rotor, partly the deflection of the rubber seals. But you'll need someone smarter than me for the actual inner workings. As long as the cylinders and pads can move freely and the master cylinder isn't staying pressurized (is there a relief hole in these?) I'd just ride it.

 

[Unkle Crusty]

When the brake pad is pushed, it tends to roll the seal a little. With the pressure off, the seal relaxes and rolls back a little. This is a teensy amount, but enough to do the job. It is mostly the lack of pressure that keeps the pad off the disc. There is a magic grease especially for the seals. Some folks do not use it, and only use brake fluid. I have had much better results with the special grease. Some pad and parts kits have the grease included.
Anti seize on the edges of the pads is a good idea. The metal parts. And the piston needs to be squeaky clean.
On some vehicles like my 78 3/4 ton belch mobile. The rubber hose deteriorates inside. That prevents the fluid from returning, and holds the brake on. Old fluid can go like jelly and do the same thing.

Unkle Crusty

 

[XSLeo]

When you replaced the M/C you should have replaced the brake lines. They rot from the inside. As they rot bits of the rubber float around in the line. This often restricts the fluid return. This can hold the caliper partially closed.
I recommend you replace the lines with braided stainless lines and do a tear down, cleaning and inspection of the calipers. You may find the calipers full of crud.
Leo

 

[16VGTIDave]

Yamaha recommends replacing the brake lines 5 years from date of manufacture. So "New, Old Stock" or NOS lines are not worth the shipping cost. I had a braided stainless steel line made to my spec for about $50. It will probably outlast the bike.