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Soft Brake pedal

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Old 11-09-2011, 03:28 PM   #1
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Default Soft Brake pedal

I have a 02 f150 2 wheel drive 4 wheel disc. The problem is a soft or spungy brake pedal that will keep going down as long as you apply foot presure. I have replaced the master cylinder and I used a vacuum pump to bleed the brakes, starting with the wheel the farthest away from the master cylinder. I still have a Brake light on the dash and a soft pedal. Where do I go from here?
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Old 11-09-2011, 07:53 PM   #2
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Default Just a Guess:

Recheck the output shaft seal between the booster and master cylinder. If it may have been compromised when you replaced the MC.

Bleed the brake system starting with the shortest link and working outward progressively to the longest. Bleeding the longest path first may leave bubbles in the system.

Pressure bleeding the system is prefered to prevent sucking air into the system.

A very good and inexpensive way to bleed brakes is this: Get a 20-foot length of 3/16" tygon tubing and an adapter for one end of the tubing that will fit onto a bleeder port. Connect the adapter to a bleeder port and open the port about 1/2 turn. Run the tygon tubing around the truck and past the driver's door so the fluid running through the tubing can be seen. Run the open end of the tubing into a suitable can to catch the fluid. Fill the master cylinder reservoir with new fluid, leave the cap off then begin pumping the brake pedal slowly and firmly about three-quarters of its stroke. The brake fluid will be pumped out of the bleeder port, down the tubing and the run-off collected in the can. Keep pumping slowly but firmly until all the bubbles in the tubing are cleared and all the old fluid pumped out. Keep the master cylinder reservoir full as you go along. Close the bleeder port and proceed to the next one.

Last edited by Kattumaram; 11-09-2011 at 08:37 PM.
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Old 11-13-2011, 10:26 PM   #3
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Did you bench bleed the MC first? If not it will take you quite awhile to bleed the air out of the system. I remember that on older Fords you had to pull a pin on the proportioning valve to properly bleed the brakes. Otherwise when bleeding the difference in pressure frt to rear would result in the proportioning valve going over center and not not allowing you to properly bleed the brakes. (I dont know if this applies in your case)

Always bleed the wheel farthest from the MC first. And make sure the MC reservoir dosen't run out of brake fluid or you will have to start over.
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Old 12-02-2011, 12:29 AM   #4
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If you didn't have the problem before you worked on the brakes and are sure you have followed the proper bleeding, than look for a bad master cyl. If the cup is leaking thru it won't pump up. Keep in mind that the new brake systems tend to have a soft pedal that moves down toward the floor as you push on it. Does your truck have anti loks? If so the pedal is softer to start with. You may not have noticed them until now.
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Old 12-02-2011, 12:29 AM

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