Have an issue with my Ender 3 bed. I can't level it no matter what I do and I've been at it for days now.

I've bought numerous sheets of glass and mirrors from a local supplier and when the aluminum heat bed is loose (no tension in springs) or removed from the y carriage the glass or mirror sits fine, but go to level or tram it to the nozzle in the four corners and the glass or mirror just rocks due to two

diagonals being higher the then the rest, yet my nozzle is positioned correctly. If i secure the sheet with bulldog clips i eventually run out of adjustment going round the four corners. I've tried obiviously glass and mirrors to flatten it, used 0.5 thermal pads, taken apart they carriage even drilled the holes

larger in the y carriage in case they weren't drilled correctly from the factory and was causing it to bulge. Any one have any suggestion because at the moment this it just a big deadweight.

My son bought a Ender-3 last week. He just needed to adjust the tension on the rollers for the various axis. It's working nicely although he did need to tighten the bed a bit as too little compression on the springs allowed the bed to move.

Investigate how square the rails are to each other.
In particular the Y rail being higher or lower at the rear verse the front. You may have to check/adjust (don't know how you adjust) the X rail.
This is not easy to do. Might be easier to use a spirit level so gravity becomes a common reference point.