Brake pedal sank to the floor!!! then was fine?

[BlueBreadTruck]

I got in my truck this morning, hit the brakes, and the pedal went to the floor! I thought I had blown another brake line.... I hit the brakes again and it was perfect, and has been perfect all day? What is going on here? Also, it seemed to be an issue with the rear brakes. So, Im thinking RABS or Master cly? Anyone ever have something similar happen?

 

[franklin2]

If your rear brakes are really really out of adjustment, it could possibly cause this, though if you let it sit for a little bit, the problem should somewhat come back till you push the shoes out to the drums again with the pedal.

 

[typ4]

If its not adjustment it could be MC. Just out of curiosity did it get real cold since you drove it last. I had the reservoir suck the bore partially empty once in this scenario.

 

[BlueBreadTruck]

If its not adjustment it could be MC. Just out of curiosity did it get real cold since you drove it last. I had the reservoir suck the bore partially empty once in this scenario.

YEAH! It got very cold that night. Ok, so im on the right track here. As far as I can tell, it still has the OEM M/S. Im going to order up a new one for good measure. Thanks!

oh, and yeah, all the brakes a brand new, front to rear