Brake Fluid and it's effect on brake performance

Losing fluid somewhere or losing pressure in the master. Will need to be serviced by a shop. Can't drive it this way.

What you are describing is brake drag. Brake drag occurs when there is still fluid under pressure left in the brake lines. When you apply brake pressure, brake fluid is pushed into the brake lines from the master cylinder, with a piston. During normal operation, when released, the brake pedal should return to a resting position as the brake fluid returns to the master cylinder. Brake drag may be caused by any of the following:

A) The master cylinder piston is not returning far enough for the brake fluid return into the compensating port.

B) Topping off the master with automatic transmission fluid, engine oil, or power steering fluid, can well the rubber seals in the brake lines. The mineral oil in these fluids can affect the composition of the rubber in the brake line.

C) The master cylinder push rod could be out of adjustment.

You problem could be caused by, but is not limited to, any one of these symptoms; each and every car is different, and some have problems that can stump the greatest technicians for weeks, so do not take this as your solution, but rather a place to start.

Start from right rear, then, left rear, right front, left front. Fill master cylinder. Have helper sit in car, have helper hold brake pedal down. open bleed screw. fluid and air comes out. close screw. release brake pedal. Continue until no air comes out. Move to next wheel. Keep an eye on master cylinder fluid level after each wheel.

The most common bleeding procedure is to bleed the ABS brake furthest from the master cylinder first, then bleed the other brake that shares the same hydraulic circuit (which may be the other rear brake on a rear-wheel drive car, or the opposite front brake on a front-wheel drive car or minivan). After these have been bled, you then bleed the other brake circuit starting with the furthest brake from the master cylinder.
Air can be very difficult to remove from an ABS modulator assembly because of all the nooks and crannies inside the unit. The modulator may have eight to 10, or more, ABS/traction control solenoid valves, plus various check valves and dead-end ports. Some ABS modulators have special bleed screws to help you vent the trapped air when bleeding the system. Others do not and require the use of a scan tool to cycle the ABS solenoids while you bleed the system. 1. To bleed the isolation valves in the modulator, there are two bleeder screws. Start with the one toward the engine. Turn the ignition on and apply light pressure on the brake pedal. Open the bleeder screw and allow the fluid to flow until clear. Close the screw and do the same at the second bleeder screw. 2. Depressurize the accumulator by pumping the pedal 40 times with the key off. Wait about two minutes for the brake fluid to de-aerate, then refill the fluid reservoir with DOT 3 brake fluid. 3. Now you can bleed the boost section. This is done by applying moderate pressure on the brake pedal and turning the ignition on for three seconds, then off. Repeat this a total of 10 times. Make sure the pedal feels firm when you have finished, and give the car a road test to make sure the brakes are working properly.

Try using a pressure bleeder. It will force the air out. Works every time.