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Old Apr 10, 2021 | 04:08 PM
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Soft brakes

Can a bad hydrobooster cause loss of brake pedal, much like a bad master cylinder. When you first hit pedal brakes work. But as you sit there the pedal slowly falls.
 
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Old Apr 10, 2021 | 06:53 PM
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Why do you not suspect the master cylinder?
 
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Old Apr 10, 2021 | 07:53 PM
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We installed a new master cylinder (not a reman unit) and no change in pedal. Also when bleeding brakes fluid came out of vent on power steering pump (it was over full). Doesn't seem normal, it had enough force to land on the outside of fender. Sorry should have put it all in first post. Was in rush
 
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Old Apr 10, 2021 | 09:59 PM
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Just to confirm some things:

Did you replace the brake fluid?

Is the PS reservoir at the right level now?

And the PS reservoir is filled with Mercon not PS fluid, right?
 
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Old Apr 11, 2021 | 06:05 AM
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Yes, on all questions, truck was wrecked and we are rebuilding it. Almost done with it. Last issue is the brakes
 
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Old Apr 11, 2021 | 07:10 AM
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How much brake fluid did you flush through while bleeding? Replacing a master cylinder means all the lines have air in them from the very start that needs to go through the entire length. Did you cycle the ABS pump while you were doing it? Were you using a pressure bleeder?

Did you have your PS pump spinning while you did the bleeding if you weren't using a pressure bleeder?
 
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Old Apr 11, 2021 | 08:03 AM
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Dont know total on brake fluid but a liilte more than 2 gts.
bleed until clear fluid came out and a little more.
did not use pressure bleeder, wife was working pedal.
dont know how to cycle abs.
truck was not running while bleeding
i dont have much experience with hydro booster.
but have fixed many brakes, and didnt need truck running. I will try that
 
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Old Apr 11, 2021 | 08:07 AM
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You need a scanner and software to bleed the ABS. Auto Enginuity can do it but I also think that ForScan can as well. ForScan is much cheaper and most popular these days. Alternatively, I have also read that you can find a loose gravel road and go lock 'em up to get it bled but I am not sure on that one.
 
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Old Apr 11, 2021 | 12:08 PM
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I read about the gravel road thing too, i tried that due to the abs light being on. The abs light went out. But the brakes are still doing same thing.
i will get my AE this afternoon and try that too.
 
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Old Apr 11, 2021 | 12:21 PM
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@R&S20 I highly recommend a pressure bleeder because it allows you to flush a larger volume of brake fluid faster which aids in getting rid of bubbles stuck in the lines due to capillary action. Plus it frees your wife from having to pump the pedal which is an activity that inspires a lot of wives to tell the husband to get rid of the damn truck.
 
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Old Apr 11, 2021 | 02:03 PM
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I bought a power bleeder on the recommendation of FordTruckNoob and it is one of my favorite tools now. I can bleed the brakes by myself at all 4 corners in 10 minutes. No mess, no standing around drinking beer while they gravity bleed. No hollering at the wife to push the pedal in or let the pedal out while your turning a wrench on the bleed valve.

Power bleeder has many caps for many manufacturers. Luckily I only had to buy two caps that fit our Subaru, VW, Ford Escape and 7.3L.
 
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Old Apr 12, 2021 | 07:02 PM
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I appreciate the advice on a power bleeder, but the wife dont mind and this is our sons truck. She will wear out the pivot points before she quits.
so to the original question can a hydro booster mimic a bad master cylinder?
 
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Old Apr 12, 2021 | 07:25 PM
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Originally Posted by R&S20
I appreciate the advice on a power bleeder, but the wife dont mind and this is our sons truck. She will wear out the pivot points before she quits.
so to the original question can a hydro booster mimic a bad master cylinder?
Where it stiffens at first then slowly goes all the way to the floor? Not likely.
 
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Old Apr 12, 2021 | 08:04 PM
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Ok, Fordtrucknoob
that is what i was looking for, thanks again
 
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Old Apr 12, 2021 | 08:05 PM
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I'll add this: When I did my brakes I bled and bled just like you. I didn't own a power bleeder at the time nor did I activate the ABS. Left on a trip and they still had air in the front, would grab and pull slightly. When I returned home I hooked up a clear line to each front bleeder one at a time, fastened it so the end was higher than the master cyl and opened the bleeder, letting it gravity feed, I did NOT touch the pedal. After doing each side and seeing air bubbles rising out of the tubing all was good and my brakes are very solid now. It is possible that the trip I took pushed the air out of the ABS and into the calipers, it was a long trip with many dirt roads. have since bought a power bleeder for another vehicle but have yet to use it on the PSD. Your issue does not exactly match mine but mentioning this in case you may have some air.
 
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