1992 Ford F-150 Brake Booster?

Tiny
CARIESCOINS
  • MEMBER
  • 1992 FORD F-150
  • V8
  • 4WD
  • MANUAL
  • 90,000 MILES
My brakes will work fine and then go out and then work fine again. It's very random. It's happened while driving down the road and out in the trails. When they go out, the brake pedal goes all the way to the floor and there's no pressure at all. I pump the brake pedal and then they work again. What could be causing this? Could it be the brake booster? I have already replaced the master cylinder and brake pads. All lines have been bled.
Thursday, July 8th, 2010 AT 8:12 AM

5 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
The booster only makes pressing the pedal easier, so I would say no to that. If the brake pedal is going to the floor, you either have a leak (steel line) leaking wheel cylender (rear brakes) a rubber brake hose to the front caliper expanding, or you have a another bad master cylender. Check those things out and let me know what you find.

Joe
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Wednesday, March 10th, 2021 AT 12:47 PM
Tiny
CARIESCOINS
  • MEMBER
  • 3 POSTS
Absolutely no leaks. All has been replaces except the back brake cylinders. Everything is new. We've put 2 new master cylinders on it and bench bled both. New brake booster and lines. Would ABS Block cause this problem? I unplugged wiring harness from it and it still does it. It only happens at low speed. They go to the floor, pedal stays at the floor, does not come back up and then the brakes suddenly work again! What the heck is going on? Vacuum? I'm baffled!
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Wednesday, March 10th, 2021 AT 12:47 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
If everything is new including the master cylender, properly bled, the only thing left is the ABS. However, I'm sitting here thinking and I can't think how it would cause the brake pedal to go to the floor. I am assuming the rear wheel cylenders (the only thing left) are not leaking and there is no air left in the system. The only thing left is the ABS system. Is this problem what caused you to start working on the system or did it start after you the work?
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Wednesday, March 10th, 2021 AT 12:47 PM
Tiny
CARIESCOINS
  • MEMBER
  • 3 POSTS
This problem is what caused us to work on the brake system. Just put new rear cylinders on and have disconnected and bypassed the ABS block and still having the same problem.
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Wednesday, March 10th, 2021 AT 12:47 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Did you bleed the brakes starting from the farthest point from the master cylender and moving closer?
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Wednesday, March 10th, 2021 AT 12:47 PM

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