Brake lines need to replace lines from master cyl. to abs pump. cant trace lines.

Abs systems are harder to bleed but it is quite possible the the bleeder screw is just plugged up. Pull the bleeder screw completely out and see iff you can blow through it and see if brakefluid finally comes out of caliper. If it does not trace the line backwards and crack lines open to see when and where the clog begins. Sometimes the abs unit can become clogged because brake fluid breaks down and becomes a sludge because hardly anyone flushes the brake fluid anymore. Brake fluild needs replaced after atleast by second brakejob, otherwise it breaks down from all the heat created from pressurizing and depressurizing in the brake system. Good luck finding your clog. I would advise removing your brake master cylinder reservoir and clean it out and clean out the brake ports in the master before reinstalling. Flush your whole system and your brake system will last for many more years.

I had a experience with a car that REFUSED to let all air out its lines, and a friend of mine bought 4 vise grips, and gently grabbed the three hoses (from each wheel) that where not beeing bleed.
first he grabbed all four wheels, and notices a slight mush on the pedal and said that the master cyl was not properly bleed, he bleeded the cyl in a bench, then assembled the cyl and now the pedal was very stiff, then procedded to remove rear-right hose, and the pedal almost went to the floor, THERE WAS THE BUBBLE!, and bleeded acordingly, then reatached the vise grip on the OK line, and released the one on the rear-left, slight mush and bleeded, and so on. each time he tested for possibly air bubbles in each sector (master cyl, or lines, or caliper or aux cyl itself).
BUT!, IF your master cyl is NOT pumping fluid to the rear, probably the proportioning valve is broken (if yours has ABS, might the abs valves are dirty, and thus NOT closing and letting pressure go other way, because a failed abs pump SHOULD behave transparently, I mean , not interfering with the braking operation)
get quality FLARE WRENCHES, because the air bubble MIGHT not be right in the bleed bolt in the caliper/aux cyl.

Best case scenario bad vacuum pressure to the brake booster. Worst case bad abs control module or valve body/motor the abs system works by add and removing hydraulic pressure through valves and electric motor. Try using block off plugs at the master cylinder( remove lines plug outlets at master cylinder) check if brake pedal position and pressure is good(if there is no change problem is master cylinder or brake booster/ vacuum) if plugging at master cylinder solved issue repeat procedure at abs valve body after reinstalling lines from master cylinder if your problem returns your issue is in the abs valve body if plugging at the abs solves problem reconnect at the valve body bleed each line one by one testing between each line until you find the problem

there is still air in the system. To bleed the brakes bleed out the m/cyl first by loosing off the lines at the cylinder v/ This primes the master cylinder first. Then starting at the longest line first bleed out the air finishing at the shortest line

The ABS brain block is defective! Will have to be replaced. Big aluminum block with a lot of lines to it. =Usually down low under the master cyl.

some vehicle made by GM require special sequence bleeding and a scan tool to open the abs brake module to bleed all the air

Did you try adjusting the rear shoes? If out of adjustment they would have to travel farther giving you a low pedal. Also did you try bleeding the abs unit?

you may have a ABS problem. I would drive it and attemp to skid the tires an dsee if the pump activates. sometimes this will unstick any valves inside the ABS unit. you may need to have a qualified repair shop check deeper. the ABS will have a code, and a scanner will be needed to check further.

Hello,
I hope this helps.







Thank You,
Roy

you will need to replace your master cyl and bleed your brakes
your master cyl is bypassing inside or the seal are bad inside the master cyl
there isnothing slse in the system that could cause this unless you are loosing fluid.
good luck