If you didn't bench bleed the new master the pistion inside will jam forward and cause the front calipers to lock since the fluid cannot return to the reservoir. I learned this the hard way, but a word of caution for you do not expect it to remain locked the fluid will slowly return to the reservoir releasing the calipers, I also found this out the hard way when I was test driving my truck. I hit the brakes at a stop sign and they would not release so not thinking about it I hopped out to check it out, I even left it in drive all of a sudden I heard them release and barely made it back inside my truck. Not being a big problem normally but I lived at the top of the foothills and this was the 1st downhill stop of a very long hill straight down for about 2 miles.