The problem is due the master cylinder being partially activated. If you drive a longer distance, the brakes would lock up again.
I see you have been going through a lot of work and the problem is still not resolved. You mentioned the Toyota tech saying the adjustment was out by 10 mm. You must be kidding or the tech does not know what he is talking about. A 1 mm difference is possible but a 10 mm difference would not allow you to bleed the master cylinder or brake system after replacement of the master cylinder.
The master cylinder has dual chambers and each chamber supplies pressure to 2 wheels. This system is a diagonal system meaning, FR + RL for one chamber an FL + RR being supplied by the other chamber.
Did you check the pedal free play? If the brake switch is out of adjustment, it can result in the brake pedal being partially depressed causing the problem.
Booster rod adjustment is rather troublesome and if pedal adjustment is not the cause of the problem, you would still need to get this done. I have a suggestion which you could try.
When problem occurs, loosen the master cylinder holding nuts slightly and pull the master cylinder away from booster. If brakes releases, it means the adjustment is out. Remove the holding nuts. Make 2 washer with a thin card board and place one each between the master cylinder and booster stud. Reinstall the master cylinder and retest. You may need to repeat this again with addition of gasket to increase the clearance if necessary.
Monday, July 4th, 2016 AT 4:19 PM