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Old 09-15-2016, 10:47 AM   #15
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It finally dawned on me what your problem probably is .

This post is from my work on Chrysler products with anti-lock brakes , Ford may do things differently, so I'll apologize in advance if this isn't your issue and the test doesn't work.

Anti-lock brake systems have a fluid pump and a pressure accumulator. ( to provide brake fluid under pressure , instantly , during the cycling of the anti lock brakes ) .
The accumulator pressure is built up by the electric pump when the key is on.
I believe what's happening in your case , is that what ever valving that is supposed to hold that pressure in the accumulator , is failing allowing the fluid back into the master cylinder reservoir.
To test if this might be your problem , drain some fluid from the reservoir , then with the ignition key OFF, pump the brake pedal about a dozen times.
Pumping the pedal should drain the accumulator pressure, and the brake fluid level should rise in the reservoir . Then you can wait and check the level in a while to see if the level is now stable.
If the fluid level is stable then you've found your problem , unfortunately , I don't believe it will be a cheap repair as the pump and accumulator will be sold as an assembly.

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Old 09-15-2016, 11:30 PM   #16
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Thank you! I will definitely give that a try.

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Old 09-18-2016, 08:58 PM   #17
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Brake fluid will in fact pick up moisture since it is hygroscopic but you will never have enough water in the brake fluid to cause this problem unless someone filled it full of water. You do have a strange problem, in 40 years of being a technician I have never heard of anything like that. When you release the cap is there any pressure in the reservoir? As for the caliper Pistons causing this, they'd barely move as the only thing moving them is the square cut seal going back to its at rest position.
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Old 09-19-2016, 04:59 AM   #18
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No. There is not any pressure when I remove the cap but it is full right to the lip of the reservoir. I am very confused on what would cause this. We have owned this coach for 5 years and never have had one problem. Like I said earlier...we took a 3000 mile trip and never had a problem til it was parked on our driveway 3 weeks later. Even if there was water in the system it is not nearly hot enough to push it out the reivoir.
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Old 09-19-2016, 07:14 AM   #19
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Just wondering...could the Hydroboost be pushing fluid past the master cylinder seal thus into the reservoir?
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Old 09-19-2016, 07:36 AM   #20
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Very doubtful. I suppose anything could happen.
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Old 09-24-2016, 09:53 PM   #21
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Originally Posted by johnhicks View Post
Just wondering...could the Hydroboost be pushing fluid past the master cylinder seal thus into the reservoir?
Wondering also about blown seal in hydroboost if:
Reservoir overfilled when cold, fluid expands particularly in warm weather or extended braking situations. The "max" marker is usually no more than 2/3- 3/4 of reservoir capacity.
The moisture thing is possible too. I have seen race vehicles boil over brake fluid.

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Old 10-02-2016, 05:01 PM   #22
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I've noticed several references to the Hydro-boost braking system. If your coach is built on a 16,000 lb. or 18,000 lb. chassis it will have the hydro-boost system. However since it's a 38' model I would suspect it is built on a 20,500 lb. or larger chassis.

The 20,500 lb. 22,000 lb., 24,000 lb. and 26,000 lb. chassis use a Hydro-Max system. Here's a link to the Bosch Hydro-Max Hydraulic Brake Booster and Master Cylinder technical manual.


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brake, fluid

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