I still have a spongy brake pedal after replacing the master brake cylinder and power brake booster. The truck is a 2000 F-150 XLT . All brake pads have been replaced as well as bled all brake lines and checked for cracks/splits in rubber and metal lines. truck does have abs system at front and rear tires. truck has disc and pad system throughout. there is no abs trouble light on at this time.

 

If you are sure all brake lines have been bled properly and fluid levels are good, you may want to consider upgrading to breaded break lines.

 

would that be Wheat or Rye Bread???

ditto on new flex lines.
Maybe try bleeding it again too... make sure you don't bounce the brake pedal against the floor when you bleed... if you push down to hard you can actually over drive the pedal and then it will bounce back slightly, sucking air in at the wheel.

 

LOL you got me on that one. Lets try it again...."Stainless Steel Braided Brake Lines"

 

Did some research and one suggestion was that, I may have gotten a defective replacement master cylinder.The second was that there may be something causing the dump valve to be partially stuck open. This will also cause a spongy pedal. Any suggestions would be appreciated.
P.S. I have replaced the brake fluid with the Synthetic Dot 3 fluid and was wondering if this performs different than regular Dot 3 fluid ? The only thing I read about was that silicone brake fluid which I'm not using,when agitated forms small bubbles.

 

Found a thread that suggested adjusting the push rod for the mc to activate quicker. This partially helped, now the pedal goes about half way before there is resistance. I tried to see if the abs system would work by doing a roadtest yesterday, but I didn't feel the typical pulsating of the pedal.

 

Byron,

Did you ever resolve this issue.. I have the same issue on my 2000 F150 XLT, new MC, new ABS pump, and bleed at the mech about 5x now and the pedal keeps going soft. Any help would be appreciated.

 

No luck yet.

 

ok stupid question but all bleeders are at the top of the cailper if not make sure the cailpers are on the right sides and you might need to manipulate the cailpers so that the bleeder is at the highest point. Another option not knowing how you bleed is a manul bleed vs. a nomatic bleed.