Hey guys. I'm having a problem and need some advice. Any help is appreciated and thanks in advance. So here we go. I'm doing the brakes on my gf's 91' pontiac sunbird. The rear are drums and I'm replacing the wheel cylinders as well. I switched it out with the new one and bled the brakes. The pedal felt firm and I had my gf press on it one last time so I could watch it and make sure everything was moving right and one of the pistons and the rubber boot popped off of the new wheel cylinder. I've been all over the web trying to find out what could cause this to happen. The only things I could think of would be too much break fluid in the reservoir of just a faulty wheel cylinder. But I checked to other one I bought to see it was put together any better and they're both pretty much the same. Lost for a solution.