easy way to tell if its the booster is to pump the brakes a dozen times with the engine off, that will use up the stored vacum. Pedal still squishy? Probably got air in the master or upper lines still. pedal not squishy with no vacum, but squishy with vacum is maybe the booster. Boosters do not fail often and when they do its usually a failure to provide any boost.
If the brake fluid in master was red and cloudy, it probably had water in it. So you should flush the system. Water in break fluid turns to steam when it gets hot. Steam can be compressed, so you loose your brakes, just like having air in them. Its also the water that makes fluid corrosive.
You can flush the system with gravity, just let it run out a bleeder on each wheel until it runs clear, keeping the master topped up of course. This might fix your squishy pedal as well; the air could be carried away. if not crack the connections by the booster and let them drip a bit, then tighten. pump pedal. repeat. This will help bubbles rise to top.
In tougher case, you need a helper to put light pressure on pedal while you crack lines/bleeders one at a time. ie: they hold light pressure, you crack connection, they stop pushing and hold pedal down until you tighten connection, then they let up. You will probably hear bubbles coming out. repeat until pedal is solid with engine off.
When you did the CV, did you have the brakes apart? Sure its back together right?
The fact that it leaks down after you pump it up is strange. it implies a leak somewhere so if there are no puddles of fluid under car to clue you in, maybe new master is bad. Masters usually hold pressure under high pressure and leak under light pressure when they start to go.
Topic: Master cylinder or brake booster? (Read 5175 times)
