1999 Ford Taurus, replaced leaking master cylinder, installed new brake pads, bled brake lines, pedal still soft. What else can I check?

bleed the spliter vale out uderneath car near back

Brake line busted somewhere? Is the linkage to the master cylinder intact? Master cylinder might have been installed incorrectly.

Hello Patricia,

Have you checked the master brake cylinder reservoir for brake fluid loss?

I don't suspect the master cylinder as you have replaced it... but am more suspect of a leaking brake line or fitting which should have
been discovered when you had the system bled.

The only time I ever had a rear brake problem with a 2500 series Chevrolet was due to seized rear brake caliper guide pins...as your calipers are also new that is not your problem.

If your brake pedal feels spongy and travels to the floor board you have air in the system, a brake fluid leak or a failure in the power steering system, such as a broken hose, broken power steering pump drive belt, or failed pump, would result in a loss of pressure to both the hydro-boost and steering.

Find more information here:

. Hydro Boost Power Assist Systems Operation Diagnosis and Repair

If you indeed removed all the air from the break system and it has a soft pedal. check you master cylinder.

There may be air in the lines. Bleed all your brakes starting at the farthest wheel from the resevoir, and finishing at the closest one. Try the pedal after its bled. If the pedal still feels soft or travels to the floor there may be a pinhole leak that may be spraying on the underbody of the car, or the seals in the master cylinder are gone filling the vacuum booster(if equipped). Air compresses more than oil so if bleeding works that may be the problem.

Hi:
If you have replaced all pads, and see no leaks at any wheel, and have bled your brake system, then most likely your brake master cylinder has failed.

you have air in the system or the master cylinder is going bad. Have a shop inspect and bleed for safety reasons if you can afford it.

You may have a leak in the booster or master cylinder. You can put a pressure tester on the system to test for leaks. It does sound like you have an air leak.
You can try to bleed the master cylinder, then slave cylinder, then brake lines.

5 Inspect Brake Fluid Type Brake fluid loss or contamination 10 Inspect Master Cylinder (Brake System) Worn or leaking brake master cylinder. 11 Inspect Brake Power Booster Damaged booster vacuum line/check valve, or diaphram

the master cyl must be filled and bled before install.after installing new bled master cyl,bleed all calipers.once you are sure there is no air left in system then you will need a scan tool to perform a abs service bleed.if you do perform the abs service bleed with a scan tool the brake pedal will be soft and start to fade.