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.
SOURCE: 1992 Ford F350 Dually Diesel Truck Brake System problem.
Adjust your rear brake shoes. Then rebleed the system. Start at the master cylinder Bleed master first then the wheel furthest away from the master (right rear then left rear then right front then left front. Do that and your pedal should be good.
SOURCE: Spongy brakes after bleeding them 2 times. Should I try to bleed the master cylinder or replace it?
Honestly your guess is as good as mine. But I don't think the master cylinder is NOT bad you still have air in the system. Get a big bottle of brake fluid bleed all four sides until you run out of fluid or your brakes work properly. You should divide the bottle's content in four, then use each quantity in each side. You'll be removing air and contaminated fluid from the system. Get a small hose that fits on the bleeders and an appropriate container. I have a good feeling if you do this your brakes will work just fine. I don't know how you are bleeding the brakes. I'll let you know the proper way just in case. This is a two man job, with the wheel off, have someone start the car. Have them pump the brakes a few times to get pressure. 1With the brake pedal UP open the bleeder, 2then have your assistant press the brake pedal all the way down and leave it completely pressed down. 3Close the bleeder valve, once close and only with the valve closed have'm release the brake. Repeat as necessary, bake depressed, open valve first then press brake. DO NOT depress until valve completly closed. Close valve THEN depress. Good Luck!
SOURCE: changed master cylinder on my
did you bleed the master cylinder itself? also if you have replaced any calipers or anything like that make sure they are on the right sides... bleeders should be on top
SOURCE: my brake pedal goes all the way to the floor there
fill master cylinder, start at right rear. the way I do it is make sure cap is back on master cylinder. pump the brakes a few times then hold them. have another person open the bleeder valve at the tires until brakes go to floor. hold them down until bleeder is retightened but be sure master cylinder is not out of fluid. then go to left rear and do the same procedure, then right front, then left front. check fluid and if air is all out there should be brakes. good-day ! THIS IS HOW I HAVE ALWAYS DONE IT ! heres a little trick of sorts. you can change a master cylinder, and if you bench bleed it first. and no fluid is lost from the master cylinder lines you do not need to bleed the whole system. but make sure cylinder is full of fluid before putting on vehicle and all air is out of master cylinder.
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