Kinda going crazy here. Got a call about the brake pedal going to the floor on a 94 Civic. After talking with the customer it sounds like a Master, were sure to check for any leaks on wheel cylinders, caliper, lines and hoses. We can't replicate the problem, we drive it do everything but take it on the highway. Customer's friend who's a "tech" talks to me after we can't replicate it and tells me to put a master on. We don't and tell the customer we'll have to come back out and try to replicate it again.
Customer calls back three days later, Master Cylinder got replaced by someone else brakes felt good and then when getting on the highway the same problem occurred. So I send one of my guys out again to check it out. I think maybe a defect reman got put on or whoever installed it didn't bleed it right. We bring a MC with us this time, tech can't replicate it and I really don't want to throw parts at this thing but I told him to try our MC and see if you have the same issue. Sure enough same issue. There are no leaks the loss of pressure only happens when the car is braking at over 40mph, I know this sounds crazy but its truly what is happening. The proportioning valve looks like it was replaced as it is all stripped up with paint pen. I only mention this because I'm at a loss, I can't figure this thing out and neither can my techs. Brakes feel great when driving bellow 40mph at 40mph and over loss of pressure.