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2008 F350 6.4 Just installed new Turbo Booster,

Customer Question
2008 F350 6.4 Just...

2008 F350 6.4 Just installed new Turbo Booster, Mastercylinder Brake Pressure switch and Brake peddle sw. Truck work OK for about 3 Miles then locked up all four brakes. Discovered shorted wires on Master cylinder pressure switch. Repaired and replaced. Also New Brake peddle sw is throwing a code again after clearing and installing new ones. Also now getting Trailer Brake Module Fault Any Ideas. I was thinking it might be related with PCM

Mechanic's Assistant: How many miles are on the car? Has this ever happened before?

211,000 No

Mechanic's Assistant: What year is your Turbo?

2008

Mechanic's Assistant: Are you fixing your Turbo yourself? What have you tried so far?

I am not working on Turbo. I am working on Turbo Boost and Master cylinder on the brake system

Submitted: 9 months ago.Category: Ford
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Answered in 8 hours by:
12/1/2017
Ford Mechanic: Chris (aka- Moose), Technician replied 9 months ago
Chris (aka- Moose)
Chris (aka- Moose), Technician
Category: Ford
Satisfied Customers: 54,094
Experience: 16 years experience
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Can you tell me which codes are currently stored?

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Customer reply replied 9 months ago
After replacing the Hydrobooster, Mastercylinder and Pressure Sensor on Mastercylinder while driving I got P0703 Brake Circuit B Error. I replaced the switch and everything was normal. Drove about 1 Mile and brakes started to lock up by time I returned to drive it was completely locked up and code P0703 was set again and the Cluster display presented Trailer Brake Module Fault.
I am getting a new Trailer Brake Module this morning and will replace it. But circuit checked out OK
Since I found the wiring to the pressure sensor (not Cruse Control sensor) on the Mastercylinder melted and shorted I repaired it where shorted just below the Sensor. Traced per Ford Wiring Diagram Manual Circuit checked out and the truck drove normal for the first test drive. It was the second time I drove it that the brakes started to locked up. I then replace the Peddle Position switch and drove it for a third time and it locked up and through P0703 and Trailer Brake Module Fault.
I have the Ford Wiring manual. I have a Electrical Engr. and Mechanical Design background. I was considering it could be a wiring harness or possible ECM/PCM. Lifting the cab is not a option my personal shop is 5.5 hrs away.
I wanted to determine if any other possibilities could be causing the issue. I was thinking also it could be the Hydrobooster peddle shaft extending to deep into the master cylinder and applying brakes but the truck rolls free off a slope when engine running and no brakes applied so I ruled that out.
Here is the real Question as well. After the truck sits over night the pressure is back to normal and the brakes are released. I can drive it but it starts all over again the cycle. Brakes locking up and have to wait until the pressure drops on it own. No Bleeding.Your thoughts! Bad Mastercylinder? Electrical System? When I trace out circuits no fuses blown. But getting these codes. I can clear them then drive it and get codes.
Customer reply replied 9 months ago
I canceled the phone call request. This is my work truck and I need to get the issues resolved. Please respond via. messaging.
Ford Mechanic: Chris (aka- Moose), Technician replied 9 months ago

Back online now, looking over your comments now.

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Ford Mechanic: Chris (aka- Moose), Technician replied 9 months ago

I am having a hard time believing an electrical issue is applying your trucks brakes. When the brakes do lock up, have you used a temp gun to check the rotors to see which brakes are locking up?

If you open the bleeder on those affected brake calipers will they release?

Have you thoroughly bleed the fluid?

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Customer reply replied 9 months ago
They all are locked up.
I have thought that maybe the hydro booster is extending and remains extended until it bleeds off overnight.
I bleed power steering lines and brake lines.
No moisture issues.
Why would while I am driving and after stopping and driving again the brakes over a distance of travel continue to apply until all 4 wheels are locked up.
Ford Mechanic: Chris (aka- Moose), Technician replied 9 months ago

When the brakes are locked up and the vehicle will not roll, if you loosen the master cylinder from the booster will it then roll freely?

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Customer reply replied 9 months ago
I broke down the Master Cylinder and the hydro booster.
When I assembled the two units originally I asked the parts house if it was the same number as the original push rod.
We verified it together.
I went back to the parts house after I broke down everything again.
By luck they still had the cores.
I compared the hydro booster’s
Even though they had the same numbers on the push rods the rod in the new hydro booster was 1/2” longer.
Some even going back and using my original spacing between the master cylinder and hydro booster I still was to long that was causing the problem.
Ford Mechanic: Chris (aka- Moose), Technician replied 9 months ago

Glad you got it resolved. If you feel like my questions helped you find the issue then please rate my response. If not then please do not rate at all.

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Ford Mechanic: Chris (aka- Moose), Technician replied 9 months ago

Hello, Chris here again,

I am checking in to make sure you got everything you expected from my answer. The option to rate my response or reply is still available. I want to make sure you were pleased with what you paid for.

Thanks Chris

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