I have a 1986 F350, with approximately 130,000 miles. When I first got the truck I was told the vacuum pump was bad and that was the reason the brake pedal was soft and spongy. I replaced the vacuum pump and then noticed the rear wheel cylinders where leaking, I replaced the wheel cylinders and did a complete rear brake job, after bleeding the lines the brake pedal was still soft and spongy, after inspecting the front brakes I noticed one of the brake calipers where the wrong ones for the truck so I replaced both calipers and brake pads after bleeding the brakes the pedal was still soft, So thinking the last thing it could be was the master cylinder, I replaced it I bench bleed the master cylinder and installed it. Bleed the system and still have a soft and spongy pedal.
Make sure that the rear brakes r adjusted properly and do a gravity bleed on the brake system. To do so leave the master cylinder open and crack the wheel cylinders and calipers open. Top off the master and let the brake fluid flow until the fluid flows clear. Then bleed the system from furthest to closest. Start at the right rear, then left rear, right front, then left front. Do not let the master cylinder run dry. If the vehicle is equipped with a dump valve then the dump valve could be the problem also. After bleeding from the wheels then bleed the master and make sure all air is out of the system. Sometimes air gets trapped in the calipers and while it's doing a gravity bleed you can take a hammer and tap on the calipers to move any trapped air to the top of the caliper. If u still have problems then it could be a defect in the master u put on. Oh also make sure the master is parrelell to the floor. Might need to jack the front of the vehicle up to make the master parrelell. Let me know
November, 14, 2006 AT 8:31 AM
Thanks it after following your sugestions they work GREAT!