Hard Brake Peddle - Even after new Vacuum Pump - Ford Powerstroke Diesel Forum
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Old 09-17-2011, 07:38 AM
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Hard Brake Peddle - Even after new Vacuum Pump

Ok so I am back to square one with my truck. To recap I have a 1996 F250 7.3L turbo diesel /manual tranny with around 280,000 miles and runs strong, with the exception that it has a bake peddle that is ROCK HARD at times. I decided to replace the vacuum pump as I hear that this is usually the component at fault. After replacing with a new vacuum pump my brakes were still hard with no difference of improvement. I did a vacuum test to ensure that the new pump was working correctly and had positive results. While running the new pump is pulling around 26 Hg with no dip in the reading. After I shut the engine off it will keep the vacuum steady around 25 / 26 Hg for well over two minutes. (I didn’t test longer as I am told one minute is the target time to maintain vacuum). I decided to then trace the vacuum tubes to make sure that they did not have a hole that was causing a vacuum leak. I actually replaced three of the four lines from the Low Vacuum Warning “break out “. I also made sure that the serpentine belt was correctly aligned as someone suggested as well as testing the hardness of the brake peddle with engine revved up / at idle. Made no difference. The only time I can get the brakes to go back to “normal” is while driving, but at a stop the brake pedal stiffens up.
So now I am at a lost of what to try. Any thought on what I should do is greatly welcome and appreciated. You all have never let me down and welcome any advice no hatter how silly it may be. Trust me I am not above hitting two sticks together while dancing around the truck if that fixes this ! Attaches are some pictures of the testing and “break out” is that helps spure on some ideas ! Thanks again
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Hard Brake Peddle - Even after new Vacuum Pump-imag0305.jpg   Hard Brake Peddle - Even after new Vacuum Pump-imag0306.jpg   Hard Brake Peddle - Even after new Vacuum Pump-imag0310.jpg  
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Old 10-03-2011, 07:38 PM
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well...

Check valve or booster at this point.

Brake Functional Tests:

Break Functional tests.pdf
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Old 10-03-2011, 07:45 PM
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Yeah, since you checked vacuum out and it's a new pump I'd have to go with a booster issue also. Sounds like the diaphragm in the booster might be messed up causing it to bleed off vacuum.
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Old 10-04-2011, 05:26 AM
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I'd say brake booster. I had a similar problem with my '08 where the pedal would sometimes be hard to push where it felt like it was almost sticking (went out at only 115k, not 280k!) and then other times it felt like it was too soft all together. I know with the 6.4L replacing this also required draining the power steering fluid as well.
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