My 93 Mercury Grand Marquis has lost braking, its not the master cylinder think its in the ABS any ideas?

Brakes locked up this morning about 1/2 block after start up, felt like emergency brake was stuck on, then lost all brakes, they go to the floor like stepping on a plum, when car is off they can be pumped up but when ignition switch is turned they are to the floor again. No fluid missing or noticibly leaking from anywhere took off all wheels and inspected no visible probs, checked all fuses and relays I could find or think of, auto store said it sounds like a problem with the anti lock braking system? Not sure what to check or if I will be able to check or test any of this, do know that of the 4 parts they told me about for the system at the auto store the price was 650-1250 and that is not feasible or worth it. Can I disable the anti lock system? and drive without it? where shoule I look? Is any of this doable without taking it to a shop and having them put it on a machine? ANY help or advise would be appreciated GREATLY!!! Thank You in advance!|||Look for a scrapyard HCU (hydraulic control unit) to replace it with, if cost is an issue. What is the condition of the brake/fuel lines? They are known to rust out and leak through. Replacing it yourself, I would not recommend though.|||I have yet to see a HCU for ABS cause no pedal pressure. This would be a law suit waiting to happen. But back to point, disconnect the wiring going to the HCU or find/remove the fuse for the HCU, it will set codes, but it will be disabled. You didn't say whether or not that the pedal still holds pressure with the vehicle off. If the pedal regains "feel" then bleeds off, look to the master cylinder. Good Luck!|||check your power brake booster / also check to see if the master cylinder is possibly leaking into the booster. i have never had the abs system cause the brakes to fail in that fashion.|||Look into one of 2 things. Either a bad brake booster or a bad proportioning valve. These will not only give you the hard pedal but also no pedal at all. If the ABS went south have you gotten any codes from it or check engine light? My feeling is the power brake booster has gone bad. You can pump the brakes up but once you start the engine and apply vacuum you lose it. I would check a simple thing 1st like the brake vacuum hose going to the booster, They normally run directly from the intake manifold and then to the booster. the booster requires a lot of vacuum to operate. So if you lost vacuum , broke the hose or maybe the hose fell off, you will have the symptons you described.


good luck