Brake pedal falls to floor during full lock left/right with steering wheel - Ford Powerstroke Diesel Forum
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post #1 of 27 Old 10-30-2019, 11:33 AM Thread Starter
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Brake pedal falls to floor during full lock left/right with steering wheel

Hello. I have a 2003 Ford F250 7.3l 2WD / 107k miles. This problem just popped up after getting my truck back from the alignment shop. I also recently added a 2" spacer to level my 2WD truck. Anyways I was backing into a parking spot and went to turn wheels pretty much full lock and noticed my brake pedal fall to floor. I then straighten them back up and pedal went back to normal. It has done this every time I turn the wheel to full lock. I looked around and did not see my brake cables or anything pinched when at full lock. Any idea what this could be? I also finished flushing the system again last night. Ran about 1.5 quarts. Drain line was solid red (flushed it 7k miles ago so it's still pretty new). When I would lock the wheel left or right and press the pedal, the pedal would fall to the floor. I kept an eye out on the fill port to make sure I didn't run dry. I did this several times. It seemed to get better. So I did a test run and I'm still getting the pedal to the floor when locking wheel to left. Today it was falling to the floor both left and right lock after work. There is no leaking anywhere. Is it possible when the tech turned the wheels with the engine off it may have damaged something or created an air pocket? A decent amount of fluid came out the fill port when he turned the wheels. He did top it back off with Mercon V. It's only doing this when full lock. It's perfectly fine with normal turns.

Last edited by L-ight; 11-04-2019 at 04:58 AM.
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post #2 of 27 Old 11-04-2019, 04:57 AM Thread Starter
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I guess everyone is stumped on this problem, yea lol?
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post #3 of 27 Old 11-04-2019, 10:25 AM
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Were the lines removed at the top end? They are easy to mix up and cause weird symptoms


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post #4 of 27 Old 11-04-2019, 10:57 AM
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One thought - were the lines lengthened to account for the new height? Fluid level topped up?

If you're fully locked out on steering wheel - maybe it's sucking air in the PS pump (used to power brakes)?

Rack could be bad causing a pass-through leak I suppose - not sure if that would lead to symptoms you describe.

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post #5 of 27 Old 11-04-2019, 11:05 AM Thread Starter
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Quote:
Originally Posted by 7.3_TurboDiesel View Post
Were the lines removed at the top end? They are easy to mix up and cause weird symptoms


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No lines were removed. Only line removed was the return for the PS pump that was on the hydroboost to flush the system. As stated I did this before 7k miles ago with no problems. I did the same procedure again when I discovered this problem thinking there may be air in the system.
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Originally Posted by Arizona_SVO View Post
One thought - were the lines lengthened to account for the new height? Fluid level topped up?

If you're fully locked out on steering wheel - maybe it's sucking air in the PS pump (used to power brakes)?

Rack could be bad causing a pass-through leak I suppose - not sure if that would lead to symptoms you describe.
No lines were lengthened. I locked the wheels and checked out the hoses and they were not kinked or pinched. They still had a little play in them. Fluid level is at correct level. It would be one heck of a coincidence that the rack went bad right after alignment. Truck only has 107k miles on it. Driven in South Texas so no rust, etc.
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post #6 of 27 Old 11-05-2019, 04:09 AM Thread Starter
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So I also noticed that when the pedal goes to the floor it still brakes, but at the end of travel. So luckily I still have braking power, but unfortunately the pedal should not be falling to the floor that far. I wonder if this is being caused by a bad master cylinder?
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post #7 of 27 Old 11-05-2019, 05:18 AM
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That does sound like a bad master cylinder, but itís odd that it only happens when you turn. Pump the brakes a bunch of times as you come to a stop with the wheels straight and see if the pedal bites at the same place every time


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post #8 of 27 Old 11-05-2019, 05:21 AM Thread Starter
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Quote:
Originally Posted by 7.3_TurboDiesel View Post
That does sound like a bad master cylinder, but itís odd that it only happens when you turn. Pump the brakes a bunch of times as you come to a stop with the wheels straight and see if the pedal bites at the same place every time


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If I pump the brakes while in the locked turn they do not get stiff. Pedal still stays soft. Once I get out of the locked turn then pump once or twice it is all back to normal. I hate to start replacing **** and it not being the culprit.
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post #9 of 27 Old 11-05-2019, 05:53 AM
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Problem is in the hydro-boost unit -- when you steer to lock it is applying too much pedal boost

Surprised you have not blown one of the rubber brake lines -- prolly is ballooning one of them

In my defense, I was unsupervised
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post #10 of 27 Old 11-05-2019, 06:05 AM Thread Starter
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Quote:
Originally Posted by Hydro View Post
Problem is in the hydro-boost unit -- when you steer to lock it is applying too much pedal boost

Surprised you have not blown one of the rubber brake lines -- prolly is ballooning one of them
No sign of stress/ballooning from the hoses either. All look great. If I am correct you would see the wear/stress on the hose from ballooning, right? This is what I was thinking as well. It can't be the MC due to it only happening during a full lock. If pedal is falling during full lock it would have to be in the hydroboost/PS unit.
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