Brake Trouble, Help!

[lexus22]

Driving last night and brake pedal went down almost to the floor but when pressed again was at the top again. This was happening on and off without warning, not good! The front calipers were rebuilt a few months ago and car been fine since then, cant see it being a problem there...has anyone had this happen before or has any idea what is causing it??

[ROYT]

Usually caused by air in the brake system

Check each wheel for leaking brake fluid.

Check brake fluid level is not so low as to allow air into the system.

If not these may be a servo fault, seek professional help!

[lexus22]

Usually caused by air in the brake system

Check each wheel for leaking brake fluid.

Check brake fluid level is not so low as to allow air into the system.

If not these may be a servo fault, seek professional help!

Thanks Roy, checked for any leaks but all ok and brake fluid level not dropped. Have used car since and no problem at all, i'm thinking possible internal seal fault with the master cylinder, but need it to happen again before stripping it down.