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Brake pedal soft

Tiny
SUBBERTS
  • MEMBER
  • 1999 FORD EXPEDITION
  • V8
  • 2WD
  • AUTOMATIC
  • 243,000 MILES
I just changed by front disc's, pads and calibers. I have bleed the line a dozen times now. Went and changed out the master cylinder, and re-bleed the brakes half a dozen more times. I can not get the brake pedal to remain firm. When I bleed the brakes I get good flow from the rear lines however on both the front brake lines the flow is low. I have been told that it could be the lower hoses on the front end causing it. Also told my need to change out the Brake Booster. I had good brakes before change now am getting very little. If I push the pedal to the floor the rear brakes lock up howevr there is little movement on the front brakes.
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Saturday, November 14th, 2009 AT 9:13 AM

9 Replies

Tiny
MATHIASO
  • MECHANIC
  • 1,209 POSTS
Did you bench bleed the master cylinder before installation?
The new master cylinder should come with the instruction.
Ask if you do not have them.
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Saturday, November 14th, 2009 AT 9:49 AM
Tiny
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Yes I did it twice to make sure I did it right, was getting strong flow from master cylinder
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Saturday, November 14th, 2009 AT 11:19 AM
Tiny
MATHIASO
  • MECHANIC
  • 1,209 POSTS
If the booster is difectiv your will notice that much higher pedal effort is needed to stop the car and that the pedal feels harder than usual.
there is no problem with the booster.
the problem is with height sensing proportioning valve. because you're having rear wheel lock up Have you replace any part on the proportioning valve lately? ot any part in this picture?


https://www.2carpros.com/forum/automotive_pictures/46384_0900c152801e5ad7_1.jpg

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Saturday, November 14th, 2009 AT 12:06 PM
Tiny
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I just bleed the master cylinder again on the SUV, when the car is off the pedal feels firm however when you start it, the pedal goes all the way to the floor. Still have good back brake movement almost none on the front brakes.
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Saturday, November 14th, 2009 AT 12:24 PM
Tiny
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I have not replaced any valves to speak of on the vechile, the picture is blurrey however am I looking for the valve at the rear of the vechile per the picture?
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Saturday, November 14th, 2009 AT 12:27 PM
Tiny
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None of the parts dealers list a proportioning valve on the 99 Expedition may it have a different name or be a dealer only part?
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Saturday, November 14th, 2009 AT 12:40 PM
Tiny
MATHIASO
  • MECHANIC
  • 1,209 POSTS
You have a diagonaltlt split system, means you should bleed the brake diagonally.
air got in the system when you replaced the caliper.
do it this way:
bleed fron/right
bleed rear/Left

then

bleed front/left
bleed rear/right.

Do each one until there is no air bubles coming out.
let me know how the brake pedal feel .

Heres a couple guides to read, they will help

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

https://www.2carpros.com/articles/brake-caliper-replacement
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Saturday, November 14th, 2009 AT 12:48 PM
Tiny
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Still the brake pedal feels even preasure while the car is off, however when you turn it on nothing. Have added four bottles of brake fluid so far. The front lines still have low fluid flow while the back have strong fluid flow.
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Saturday, November 14th, 2009 AT 1:40 PM
Tiny
MATHIASO
  • MECHANIC
  • 1,209 POSTS
Could you explain how you bench bleed the master cylinder?
I believe you but I want to make sure that we are on the right path.
There still air in the system.
Make sure there is no leak at the newly caliper you installed, or other place.
Also, check the master cylinder mounting bolt for loseness.
Here is the bleeding sequences:

1 Master cylinder bench bleed
2 heigh sensing proportioning valve(there some bleeding screws)
3 wheel cylinders and brake calipers.
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Saturday, November 14th, 2009 AT 5:43 PM

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