02 Alero 3.4L. purchased new pads for the fronts, i double checked them to make sure they are the correct ones. i cant get my pistons in far enough to fit over the new pads. I tried an old brace pad with a c clamp but they wont budge.

any other tricks?

 

If the piston gets crooked even a tiny bit, it will never go back in. Be certain it is perfectly straight.
You might also try loosening the bleed valve to let the fluid out as you tighten the c clamp.
Are there any kinks in your brake line? That also would block the fluid form returning to the reservoir. Make sure there is some air space in the reservoir to accommodate the fluid that is being returned.

 

It's best not to open the bleeders. loosen the top to the master cylinder to more easily allow the fluid to return to the reservoir.
The best way to collapse the piston(s) is to use one of the old brake pads along with a C-clamp. That will ensure the piston(s) going into the bore correctly.

Now are you saying you can't get the calipers back on over the rotors with the new pads installed because the piston(s) are not seated far enough back into the caliper?
And are these dual piston calipers or single?

 

i am using an old brake pad with a C-clamp. These are single piston calipers. Also the top cap for my master cylinder reservoir was open as well.

What would be the issue if i opened my bleeders a bit?

 

Sucking air into the lines. You'll end up needing to bleed the system and that's more work than you need to do for a simple brake job.

 

I ended up pressing them down , went out and picked up a larger C-clamp than the one i had, i guess the one i was using was too small.

 

That'll do it as well.