Why does rubber boot in master cylinder cap fall out after brakes are applied?

Without getting too technical, is it possible the new Master cylinder was defective or the brake lines put on the wrong connections? Find a similar vehicle on a car resale lot and take pictures of the Master cylinder. Compare to yours.

If you have antilock brakes, there is a control box which has flow valves inside. It affects the flow of brake fluid after the Master Cylinder pushes the fluid out.

A properly equipped repair place would connect hydraulic gauges to the brake lines to see how pressure was distributed. The Mechanic would then know where the pressure drop is.

What may be happening is there are reports of collapsed rubber brake hoses. The rubber inside the hose forms one-way flaps that trap brake fluid so that the pressure can not release when you take your foot off the brake pedal. Your brakes use a combination of steel and rubber lines. This means all you need to try is changing the rubber portion of the lines to the wheel calipers.

Either your Brake Master Cylinder or your Slave Cylinder has failed. The brake fluid is internally leaking past the piston cups. First remove the rubber boot from the Master Cylinder where it comes through the firewall under the dashboard. If the insides of the boot contain brake fluid, the Master Cylinder has failed. If the boot is dry, then your Slave Cylinder has failed.

bad break booster or master cyclinder.

Your system will have to be cleaned out. Master cylinder and all the caliper cylinders overhauled. Never put anything but brake fluid into the brake system. The seals are all insind the individual cylinders.

If your brakes system has no air in it...Your master cylinder or brake booster is bad.

If the parking brake switch is not stuck and the fluid level is OK, try tapping on the fluid reservoir to see if the light flickers or goes off. (you need 2 people to do this) If it flickers or goes off then replace your fluid level sensor. (You may have to buy a complete reservoir or master cylinder depending on your car ) If this does not provide any results, then you may have an internal leak in your master cylinder or Antolock Hydraulic Control Module causing the Proportioning Sensor Switch to turn the light on. At this point. I would tow it to a shop and have the Antilock Control Module scanned to see why it has turned the light on and disabled your Antilock Brake System. I do not recommend driving the car at all until the RED brake warning lamp problem has been resolved. It is OK to operate the vehicle (cautiously) with the YELLOW Antilock brake lamp on.

It certainly sounds as though the brake fluid had been contaminated with some form of oil, probably mineral oil.

It is potentially a seriously big and expensive job to sort out as it is possible the oil has found it's way into the brake system threatening every rubber component including the hoses.

Ideally every rubber component should be replaced for the sake of long-term safety and reliability and all the pipework flushed. It would be considerably cheaper to obtain service kits for the master cylinder, calipers, etc. but there would be a great deal more work involved.

If I was faced with the problem I would replace the master cylinder or fit a service kit and then after draining the system and purging it with compressed air I would check each caliper for normal operation. If one seemed stiff or tight I would dismantle it for inspection and if there is indication of contamination the seals and the flexible hose to that wheel should be replaced.

you have two problems here, your master cylinder has a leaking seal, the low pedal is resault, the power brake booster rubber diaphram is damaged and leaking from the brake fluid that is getting into it from the master cylinder, these are sold as a unit that has been rebuilt.

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.

Remove the old master cylinder. Use line wrenches to avoid damage to the brake line fittings. Bench bleed the the new master cylinder you have purchased. The parts store will tell you how to accomplish this and sell you the necessary bleed kit (note it may be included with the master cyl.). Carefully install the new master cylinder. Reconnect the brake lines and do not over tighten. Now with a helper, bleed the brake system. Start at the Right Rear wheel. Find the bleeder located on the back side of the wheel at the wheel cylinder. It should have a small rubber cap. Remove the cap and using a boxed in wrench, loosen the bleeder valve slightly while your helper is applying steady pressure to the brake pedal. The pedal will go to the floor and you will see and hear air bubbles come for the bleeder. Tighten the valve and then tell the helper to release the brake pedal and do it all over again. Keep doing this until no air appears. Periodically check the master cylinder and do not allow the fluid level to get too low as it will **** more air into the system. Remind you helper to never release the brake pedal until you give the OK. If he releases the pedal while the valve is open, air will be drawn into the system. Now after bleeding the RR wheel, move to the LR, then RF, and finish with the LF.