2005 1500 2wd reg cab work truck 4.3l braking problem.

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macgyver

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My truck brake pedal falls/gets soft and pulsates with what sounds and feels like fluid rushing. This happens only below 10 MPH but all the time. I am leaking NO fluid, fluid level is fine. I'm sure pads and rotors are ok. Not sure if a wheel cylinder could do this? No check engine lights or ABS lights. Master cylinder? Any one ever had this and solved the issue.
 
Do you have a hydroboost system?
 
Not sure? How would I know? Did some research and the truck does not have the hydroboost.
 
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macgyver said:
Not sure? How would I know? Did some research and the truck does not have the hydroboost.
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Did you actually look under the hood at the brake master and booster? A master cylinder if failing is not speed dependant.
 
zora said:
Did you actually look under the hood at the brake master and booster? A master cylinder if failing is not speed dependant.
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Yes, I did look under the hood, and now that I know the difference between a hydro boost vs a vacuum system it uses a vacuum system.
 
macgyver said:
Yes, I did look under the hood, and now that I know the difference between a hydro boost vs a vacuum system it uses a vacuum system.
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If it happened regardless of speed and no leaks are found it would be master but the speed factor is making the diagnosis over the internet difficult.
 
The truck brakes normal at speeds above 10mph. Thanks for your input. I replaced front and back brake lines 1.5 years ago and after that it started. I'm not sure if it started immediately after though. I bled all 4 lines but did i bleed them enough, possibly leaving some air in the lines? Been reading a little on other forums. I think I should check the my hub speed sensors for rust and dirt?
 
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What did you do with the ABS system when you bled the lines, how did you command ABS system valves to open?
 
zora said:
What did you do with the ABS system when you bled the lines, how did you command ABS system valves to open?
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Not sure what you mean by command. I think I bled the line longest first to shortest line.
 
I think you need to investigate how to properly bleed an ABS system. It's not the old days where you went from the furthered to the closest. You have a computer controlled brake system with valves that have to be in the open position to bleed and that requires a scan tool capable of doing it.
 
zora said:
I think you need to investigate how to properly bleed an ABS system. It's not the old days where you went from the furthered to the closest. You have a computer controlled brake system with valves that have to be in the open position to bleed and that requires a scan tool capable of doing it.
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I will look into that. Thanks..
 
macgyver said:
Is this programming required even though i only unplugged the original abs module and then plugged it back in?
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It's because you replaced brake lines that are after the ABS module. By programming I assume you mean communicating with the module inorder to bleed the system.
 
Pulled the ABS fuse under the hood and problem went away. I now feel a speed sensor at one of my front wheel bearings is bad.
 
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