Intermittent brake failure

Tiny
JAMESF350
  • MEMBER
  • 2005 FORD F-350
  • 6.0L
  • V8
  • TURBO
  • 4WD
  • AUTOMATIC
  • 190,000 MILES
Push brake pedal all good, push next pedal goes to floor no, brakes pump pedal comes back all good, firm pedal no fade, next time push pedal goes almost to floor then brakes problem intermittent 50/50.
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Friday, March 17th, 2017 AT 4:07 PM

4 Replies

Tiny
CARADIODOC
  • EXPERT
That is the typical symptom of a failing master cylinder. The clue is you are not losing brake fluid from the reservoir.
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Friday, March 17th, 2017 AT 4:37 PM
Tiny
JAMESF350
  • MEMBER
Ok thanks that's what I was thinking just didn't want to change it to find out it was something else appreciate the input
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Friday, March 17th, 2017 AT 5:43 PM
Tiny
CARADIODOC
  • EXPERT
Don't forget to bench-bleed the new master cylinder.

Here's a trick that can save you a real lot of time. Slightly loosen the two steel line nuts on the master cylinder. Unbolt it from the booster, pull it forward, then use it as a handle to bend the steel lines upward a little. That will prevent the fluid from running out of the lines. Remove the lines, install the new master cylinder, use it to bend the lines back down and install the master cylinder to the booster. Snug one line nut and leave the other one loose. Have a helper slowly push the brake pedal half way to the floor. It should take about ten seconds for him to get there. When he hollers he's ready, or you no longer see air bubbles coming out, snug that line, then have the helper release the pedal quickly. Loosen the nut and do that a second time or until no more bubbles come out. Do that for the other line next.

By pushing the pedal slowly, fluid gets pushed down into the line and air has a chance to float back up. By releasing the pedal quickly, the fluid rushing back will wash any remaining air bubbles up into the reservoir. You'll never have to bleed at the wheels this way, or risk breaking off a bleeder screw.

Be extremely careful to not get any hint of petroleum product like engine oil, transmission fluid, power steering fluid, or penetrating oil anywhere near parts that contact brake fluid. That will destroy all the rubber parts in the hydraulic system.
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Friday, March 17th, 2017 AT 6:30 PM
Tiny
JAMESF350
  • MEMBER
Wow thanks for info very helpful
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Friday, March 17th, 2017 AT 8:40 PM

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