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Replaced hydro-boost now have soft brakes

 
  #1  
Old 05-24-2019, 06:54 AM
jhobbs26
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Replaced hydro-boost now have soft brakes

As the title says, I replaced the hydro-boost and now have soft brakes. I never cracked a line on the master. Im guessing I still have air in the system? I've bled the ***** out of it, turning L & R pumping brakes etc. I've driven it some around my small town, the steering seems fine just have a soft pedal.
 
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Old 05-24-2019, 08:27 PM
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There are two hydraulic systems involved when it comes to the brakes. There's the Hydroboost circuit and there are the brake circuits. Have you bled both?

If you don't mind my asking, why did you replace your hydroboost in the first place?
 
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Old 05-25-2019, 09:23 AM
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The original hydro was leaking atf is why it was replaced. I did not bleed the master cylinder because I never opened that system up
 
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Old 05-25-2019, 09:30 AM
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Air might have entered the brake lines if the master cylinder got tilted when you were swapping Hydroboost units. Try a full flush of the brake lines and see if that improves things.

How was the power steering after the Hydroboost replacement?
 
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Old 05-25-2019, 11:39 AM
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Steering is fine it's just the brakes.
 
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Old 05-28-2019, 07:53 AM
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I have been having the same problem. Soft pedal. I bleed both systems and the brake will be nice and hard for a couple days then goes back to soft. Lost on what the cause is. Truck only has 103k miles so it can't be a bad hydroboost.
 
  #7  
Old 05-28-2019, 09:18 AM
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In order to replace the hydroboost, you had to remove the m/c. Getting the m/c outta the way, you had to remove the hardlines attached to the m/c...theres your air.
Also what knoob said, gotta "flush"/purge the h/b
 
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Old 05-28-2019, 09:24 AM
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AFAIK the pushrod from the pedal to the master is physically coupled to act as one continuous rod, if this is correct booster condition or air shouldn't be able to cause a soft pedal. My only guess is that the master wasn't kept upright when disassembled and some air got into it, or it's got a worn cup that for some reason only became apparent after messing with it, less likely. Or there's a problem with the ABS module that happened at the same time you did the work, also unlikely.

Put the truck on an angle with the driver's side higher than passenger and pump the brake pedal at least 30 times giving a couple seconds between pumps. That should remove any air trapped in the lines near the master, there probably isn't any, but better to be sure. Then angle the truck as needed so that it's level side to side and the front of the master is a little lower than the back and do the pumping again. This should eliminate any air in the cylinder.
 
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Old 05-28-2019, 09:29 AM
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Originally Posted by timmyboy76 View Post
In order to replace the hydroboost, you had to remove the m/c. Getting the m/c outta the way, you had to remove the hardlines attached to the m/c...theres your air.
Also what knoob said, gotta "flush"/purge the h/b
I've done a few hydro and vacuum boosters without removing the lines, but not on this truck so I don't know if it can or can't be done. He said he didn't crack the brake lines so apparently it can be done.
 
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Old 05-28-2019, 09:31 AM
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Also: if the booster's pushrod is too long and doesn't let the master pistons fully retract it can cause brake bind and/or a low pedal. If the rod is too short it'll cause a low pedal. Neither condition should cause a soft pedal, but a low pedal is often perceived/described as a soft pedal. It would be worth loosening the master to verify that the rod isn't pushing on it unless you verified that during assembly. If the rod is pushing on the piston at rest it can cause problems that are hard to figure out.
 
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Old 07-09-2019, 05:25 AM
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a little update. I bled the brakes and found the RR rubber brake line was bad. Replaced both rear rubber lines, flushed entire brake fluid on all 4 wheels, bled brakes and still have a soft pedal. At this point i'm leaning towards the cardone reman hydro booster being junk.
 
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Old 07-09-2019, 10:39 AM
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You can bleed the brakes forever and if there's air in the master it can stay there.
 
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Old 07-09-2019, 11:52 AM
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^What '88 E-350 said.

Also, what method did you use to bleed the brakes? The ol' pump-n-hold-while-someone-cracks-the-bleeder-open technique? That's not going to flush air pockets out. Use a pressure bleeder that can force brake fluid through at a good pace.
 
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Old 07-09-2019, 03:02 PM
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Originally Posted by FordTruckNoob View Post
Use a pressure bleeder that can force brake fluid through at a good pace.
Not sure if this is where FordTruckNoob was going with his suggestion, but I use a MightyVac hand pump. I have used it for years on everything from the F-250 to a Suzuki Hayabusa.
 
  #15  
Old 07-09-2019, 03:26 PM
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Sort of. I was thinking more along the lines of this: Motive Products 0090 Power Bleeder Tank
Amazon Amazon

Or he could make one himself out of a garden sprayer.
 
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