I have a 1998 Ford Expedition that has a soft, spongy brake pedal that travels too far. The stopping distance is dramatically increased under this condition. With the engine off the pedal builds up sufficient pressure when pumped, but loses pressure and goes nearly to the floor when the engine is started.I've tried the following in order to fix the problem with no improvement so far.1) Checked fluid level in master cylinder reservoir....ok.2) Bled brakes at each wheel starting first at the wheel farthest from the master cylinder and ending at the wheel closest to the master cylinder....with no noticeable improvement.2) Replaced master cylinder, bled brakes again....with no noticeable improvement.3) Checked vacuum to master cylinder with a reading of about 15 inches of vacuum. Then I pulled the check valve off the power booster and it was flowing correctly in only one direction.4) Replaced power booster....with no noticeable improvement.5) Replaced front brake calipers, installed new pads and bled both front brakes....with no noticeable improvement.I'm at a loss of what to try next....does anyone have any suggestions?
Country: United StatesMake: FordModel: Expedition Eddie BauerYear: 1998Area: Brakes
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sounds like the hcu may be bad
Is that the hydraulic control unit? Where is it located?
here is a pics and yes the hydralic control unit has a valle that sticks and causes a low pedal the only way to fix is to replace it
here is the location
Is this a dealer only part and do you know if a less expensive re-manufactured unit is available?
this is a dealer only and I do not know of any places that rebuild them may be able to find it cheaper on the internet
I forgot to add that the ABS indicator light is not on when the engine is running, so would it still indicate that this is the problem?
if the pedal is sinking like a bad master amd the master has been replaced then the return valve is sticking in the hcu and allowing fluid to bleed back to the master. This problem will not turn the light on
crap gets stuck in the valve and causes it to stick see this all the time
I would imagine your beak fluid is black or was
There is a proportioning valve off the side of the master cylinder...could this be the problem instead?
no have never seen that cause a soft pedal
Yes, the brake fluid was black when I first started bleeding the system. With the number of times the system has been bled, new fluid comes through at every wheel.
then it has been flushed and the fix is the hcu
A couple of forums mentioned that improper adjustment of the parking brake could cause this....I haven't checked that yet. Could this be part of the problem?
you have disk brakes in the rear and the parking brake is separate from the regular brakes so no
there are completely separate from each other
Sounds like it must be the hcu then. Have you ever seen this problem with a defective caliper....would you suggest that I replace the rear calipers first?
if it was it would be leaking and if there are no leaks then no
There were no noticeable leaks.
then it needs a hcu like you said
Thanks for your help. I'll try replacing the hcu.
thanks for the accept
25 years working for Ford dealer. Ford Master tech.
I did some additional research and it appears conventional brake bleeding (like I did) may not remove all of the air in the system (see text in bold below). Could this be the cause of my problem and should I try this procedure before replacing the HCU?
If equipped with the 4 wheel anti-lock brake system and the Hydraulic Control Unit (HCU) has been replaced or is suspected of containing trapped air, bleed the brake system using the procedure below. Conventional brake system bleeding cannot remove the air trapped in the lower portion of the HCU.
If a spongy brake pedal is present and air in the hydraulic control unit is suspected, use the following procedure:
I assumed you had already had don that you mentioned you bleed the whole system several timesIf not give it a shot Steve40531.9555618866
I bled the system conventionally (step 1 above) several times as described in the repair manual that I have. However, I did not use an NGS tester to perform a "service bleed" using the rest of the procedure and wheel sequence above. Since I can pump up hydraulic pressure using the brake pedal with the engine off, but lose pedal pressure when the engine is started would this still indicate air in the system and thus trying the bleeding procedure above?
For air to be in the hydraulic system then you would have had to have a leak or replace a component to bleed the brakes.Since the problem started without replacing a component that needed to be bleed like the master or a caliper and you did not have a leak then I really doubt bleeding the hcu will help.But it does not hurt to try and see. Since you replaced the master you may have some air in the system. you also want to make sure you bench bleed the master cylinder before installing it. Another trick that i have preformed if you do not want to take it to the dealer is get the truck in the air put it in 4x4 and run it to 50 mph and step on the brakes it will go into hcu lock up and pulsate the pedal or basically activate the hcu and bleed the air out. This is what you are basically doing when bleeding the hcu with a ngs or ids. You are activating the hcu. click on the blue links below for installing the master and bleeding the hcu. by fords way. Especially the master needs to be bench bleed first before installing. click here proper bleeding of master before installing click here for bleeding hcu