Installing Kelsey Hayes Caliper Pistons ?

It requires a little emphasis when you push the pistons in. It could be possible the seals got cockeyed during the process and wedged your piston. I lubed mine with Dot5 and they went in ok but it would probably worth in your case to use something more slippery such as what hemi71 recommended. You will probably need to use air, etc to get them out again. I also installed dust seals first before the pistons. My restore thread has some fairly detailed pics of my caliper rebuilding process.