caliper rebuild stuck

[KWL82]

Attempting to rebuild front calipers. Have rebuild kit from AR, followed instructions exactly and watched video. Problem is the piston wont push in past the inner seal. its completely stuck. I tried brake spreader and wont budge. I dont want to damage anything. I'm wondering what the issue might be. My inner seal went in fine but maybe it sticks out too much? Is it supposed to be perfectly flush against the wall ? mine wasn't and i think maybe thats the issue? any other ideas? thanks in advance

[KWL82]

this is as far as i could get it in. does the seal look bad maybe?

[spider2081]

I usually install the piston into the caliper before I install the dust seal. Once the piston is completely inserted I install the dust seal.

The groove the fluid seal fits into in the caliper must be completely cleaned of all corrosion for the seal to sit deep enough into it.
I like to apply Silicone grease to the seal and the piston to assist assembly. Others like to wet them with brake fluid. I also check the base of the piston for sharp edges. Some pistons don't have a smooth rounded edge at the base of the piston and it can tare the new seal. Polishing that area with emery paper can help pushing the piston in.

[lglade]

At this point, I'd disassemble and inspect the seal. You may need some high pressure air to get the piston back out again, and if you do, be sure to keep your fingers clear or you could be injured. Use a block of wood and some rags too, to protect the piston when it comes out.

I use a small brass wire wheel on a 90 degree die grinder to clean up my old calipers prior to assembly and also some clean brake fluid as assembly lube. If your seal was damaged during your prior attempt, then you may need a new one. Check it carefully before you assemble again. I agree with the above advice about installing the seal after the piston goes back in.