So I just finished installing new calipers, shoes and went the bleed the brakes. After bleeding them all i noticed i could still hear air and it was coming form the master cylinder where it connects to the master vac, near the bottom. Is there a gasket that goes there? or is one or both of those broken and needs to be replaced... Also when i pressed on the brakes only the rear would lock up not the front

You heard air before? This is with the engine running, when you press the brake pedal? You might have a bad brake booster.

There is not a replaceable gasket on the brake booster, but there are rubber seals. I don't think they are serviceable. I recently replaced my brake booster with a rebuilt one from NAPA. Also, regarding only your rear brakes locking up, have you bled the master cylinder? Use those bleeder valves on the side of the master and bleed them right back into the master.

i havent bled the master cylinders yet, and i believe it started happening when i changed the rear left cylinder. I think im going to re bleed the system and the master cylinder and ill let you know if it still has air. this is all without the engine running btw

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So I've confirmedd that air is coming from mate where the brake mc and master vac mate.has anyone had this problem and know which of those 2 should be replaced

There is no gasket between the master cylinder and the Master Vac. With the engine not running the Master Vac will pump air through the vacuum hose and into the intake manifold. If the check valve is in backward or is blocked for some reason the air will have no where to go and will try to escape pass the seals in the Master Vac and exit at the joint where the master cylinder attaches. Remove the vacuum hose from the Master Vac and see what affect it has on the noise.