SOURCE: rear brakes not working on
There are seals in the master cylinder that may be bad.
Try bench bleeding the master (there are cheap tubing kits for this) and see if fluid comes out of the ports. If no fluid after bench bleeding, replaced the master cylinder (usually come with a cheap bleeder kit anyway)
SOURCE: Replaced master break cylinder bench
You have air in the system, no matter that you bench bled the Master cylinder, air got in the system that is the only cause of this symptom other than a defective new part. Follow the guide lines below to bleed brakes.
To properly bleed the brakes, start with a couple of 8-ounce cans of fresh brake fluid. An unopened can has a long shelf life. An opened can should be discarded within a few weeks. Get the vehicle up in the air and remove all four wheels, you might be able to do this with the wheels on if you can swing a wrench on the bleeder valves. PLease read through the instructions completely before you start work, do not let the Master cylinder run dry of fluid.
Have a helper pump up the brake pedal, then open the right rear brake bleeder and bleed it until you don't hear anymore air bubbles coming out and the fluid stream is steady, next move to the left rear wheel and repeat, then to the right front and bleed that wheel cylinder, then repeat at the left front wheel cylinder. A tip hear, soak the bleeders with WD40 before you try to crack them open, DO NOT STRIP/ROUND OFF THE CYLINDER BLEEDERS, Use a box end wrench to get a good bite on the bleeders. When all the air is out of the system the fluid will be steady and not make a spurting noise, do not run the master out of fluid!
SOURCE: Hi I changed the master
Hi, if you plug the port, the plunger will not be able to build pressure in the front lines as the back brake section of the master will hold the plunger back. The proportioning valve will also not let you do this, as it is trying to strike a balance between the front and rear brake pressure. I'm afraid you need to repair the rear brake lines. This is not hard work, but it does require a brake line tool for cutting and flaring the lines. You may be able to borrow the tool, or check to see how much a brake place would actually charge to replace the lines. The supplies are cheap, and the labor isn't really very long--maybe a couple hours.
You've done major work and now you'll need to completely bleed air out of the system, to get the fluid to go all the way through. You may also need to adjust the rear brake shoes.
First, bleed the Master cylinder to get fluid through it. This should have been done before installation. Loosen the lines at the M. Cylinder and fill up the reservior with brake fluid. Pump the brake pedal slowly with the cover on the M. Cylinder to prevent fluid from splashing out. Once you've got fluid coming through the M.Cylinder, tighten the brake lines at the M. Cylinder.
Bleeding the brakes is a 2 person operation. You always bleed the brake the farthest from the master cylinder, then the next, the next, and finally the drivers front brake which is the closest to the M. Cylinder.
If you are unfamiliar with this process, you need to remember that you can't let the brake fluid get low in the M. Cylinder, or you have to start all over when air gets back into the lines.
When one person pumps the brakes, after several pumps hold the pedal down as far as it will go and keep pressing to the floor as the other person loosens the bleeder valve. Don't let off of the pedal before tightening the bleeder valve. Then repeat until all of the air is gone.
Teamwork and communication. Both of my wives were able to assist me in bleeding brakes.
You will have to add fluid and repeat this process until you have a firm pedal.
One man bleeder valves work if used properly, but who tells you what is happening at the other end while you're pressing the pedal?
Good luck.
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