Expedition. Brake Fade. Not fixed with new Brake Master Cyl

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ExpeditionGuy
Posts: 1
Joined: Thu Jul 31, 2014 11:23 pm

Expedition. Brake Fade. Not fixed with new Brake Master Cyl

Unread post by ExpeditionGuy » Thu Jul 31, 2014 11:29 pm

Expedition, yr=2000, 5.4L, 4x4 auto, 110k miles, Cruise control, Vehicle location is Northern California wine country.

Brake Fade. Truck normally driven each day. Parked 2 weeks (I don't know if this has anything to do with the problem). Symptom. When braking at a constant pressure the pedal fades to the floor. If I press more quickly, I get more braking. I had the brake master cylinder replaced with a new OEM spec'd part. Same problem. Another new brake master and the symptoms remain. There is zero fluid leaking anywhere.

It seems like there is a valve that is allowing fluid to pass back and not out to the calipers. This leakage seems to be a specific volume as there is a particular rate which I can press the pedal and it goes steadly to the floor with no change in braking force. I press a bit faster and I get braking force but not 100% of the force prior to this problem.

Thanks. ExpeditionGuy

 

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carriedi
Posts: 2268
Joined: Wed Apr 10, 2013 12:42 pm
Location: Oregon

Re: Expedition. Brake Fade. Not fixed with new Brake Master

Unread post by carriedi » Fri Aug 01, 2014 10:20 am

if the master cylinder is not the problem and there is no fluid loss (leaking) and the brake hoses are all in good condition, you should look at your ABS. the electro-hydraulic unit could be bad.

can you get the pedal to fade with the engine not running? with the key off, pump the brake pedal until the pedal if hard and won't go down with vacuum asist. then try and make the pedal fade. if you cannot make it fade, hold the pedal down very hard. start the engine. the vacuum booster should let the pedal go down. do you get the fading pedal now? If you do, take your foot off the brake. then Brake again and put the truck in gear. push the brake pedal until it fades all the way down. does the truck start to roll? If the truck doesn't start to roll let the brake pedal up slowly. where on the pedal does the truck start to roll at? Just off the floor or does it stay in place until you are 1/2 to 3/4 back to the top? If your truck starts to roll right from the bottom you should look to make sure the master is good (anyone can have a bad new part) then look at you abs unit. If the truck doesn't roll until you are back up near the top of the pedal then you might not have pedal fade. Your booster may let you push the pedal close to the floor but where it activates and releases the brakes is where you see if the brake hydraulics is the problem.
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