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Sinking brakes

Tiny
DAVIDDEGUZMAN
  • MEMBER
  • 1990 FORD AEROSTAR
  • 4.0L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 240,000 MILES
When engine is off brakes are working good. When engine is on specially when rolling for stop the brakes start sinking also a hissing noise when pressing the brake pedal. New caliper, wheel cylinder and ABS hydraulic unit.
Monday, June 19th, 2017 AT 12:18 PM

7 Replies

Tiny
DAVIDDEGUZMAN
  • MEMBER
  • 6 POSTS
ABS light is on.
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Monday, June 19th, 2017 AT 12:35 PM
Tiny
CARADIODOC
  • MECHANIC
  • 33,752 POSTS
Was the brake pedal sinking before the parts were replaced? If it was not, a good suspect is the master cylinder was damaged from improper bleeding procedures.

For the ABS system, most likely a scanner is needed to open some of the valves in the ABS hydraulic controller so trapped air can be bled out. The diagnostic fault codes need to be read and recorded too to see if the problem is related.
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Monday, June 19th, 2017 AT 10:09 PM
Tiny
DAVIDDEGUZMAN
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  • 6 POSTS
The pedal is sinking before all parts was change. ABS light is on, before van was not driven for more than a year pedal was okay.
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Tuesday, June 20th, 2017 AT 8:41 AM
Tiny
DAVIDDEGUZMAN
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  • 6 POSTS
I will get the ABS scan today, thank you.
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Tuesday, June 20th, 2017 AT 8:42 AM
Tiny
CARADIODOC
  • MECHANIC
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The scanner will show a fault code that has turned the ABS warning light on. It is also usually needed to bleed the system. That may solve all the problems so I'll wait to hear how that turns out.
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Tuesday, June 20th, 2017 AT 8:16 PM
Tiny
DAVIDDEGUZMAN
  • MEMBER
  • 6 POSTS
Thanks I will do that tomorrow. When you mention bleed the system? What parts of the brake system!
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Wednesday, June 21st, 2017 AT 12:00 AM
Tiny
CARADIODOC
  • MECHANIC
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You replaced the hydraulic controller. That is going to have air in it. Typically there's two chambers that have air trapped in them. The scanner will have a menu choice that commands the computer to open the valves to let that air out so it can go to the wheels and be bled out.
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Wednesday, June 21st, 2017 AT 12:11 AM

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