Losing pedal every once in awhile

[Ben Banks]

Need some wisdom and experience out there to speak up. About one out of 10 times my pedal will go all the way to the floor on my 64 Chevelle equipped with Baer's 2 piston Trac-rotor, booster, master cylinder etc. I have never had problems before. I have bled my brakes at least 10 times on all four corners--which resulted in zero air release or air bubbles. I replaced the master cylinder (bled properly) and have verified that all my lines are not crimping in any way. I have vacuum at the booster and no leaks at any of the wheel cylinders (or any where else for that matter). Once again, when I lose the pedal it goes all the way to the floor but can be pumped back up. The pedal is not hard in any way and works pefectly 90% of the time.

The only things I have changed recently are my spindles. I put on CPP drop spindles with no issues EXCEPT that I think my caliper is not clearing the upper control arm in sharp turns.

Any ideas??? I'm at my whits end after I replaced the master cylinder. Thanks!