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08 f250 diesel no brake pedal


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f250brakeproblem
New User

Jun 5, 2018, 8:57 AM

Post #1 of 10 (142 views)
08 f250 diesel no brake pedal Sign In

Hello everyone i am stumped on my brake pedal problem and hoping someone can help me.

the vehicle: 2008 f250 fx4 with the 6.4l diesel. 250,000km.

the problem: my brake pedal started acting funny like a day ago, first push i had full pedal second push mid pedal third push low pedal then repeat the sequence over and over. on my way home i pushed the pedal and it went right to the floor with nothing. i quickly pumped it up and down three times got a little pressure to get safely off the road. ( yes i was veery lucky) the pedal still went all the way to the floor.

The troubleshooting so far: i checked the fluid level and it looks full,i did a visual inspection for leaks on all 4 corners and the lines in between with no visual leaks on lines calipers or around the master cylinder and brake booster. when i push the pedal i can hear what sounds like air exiting the system but cannot find from where. i believe what i am hearing is an internal leak in the master cylinder brake booster or abs module. any tips on further troubleshooting to resolve the issue with replacing just the part thats broken instead of replacing all 3 would be greatly apreciated.

thanks in advance for any help possible.


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Jun 5, 2018, 9:38 AM

Post #2 of 10 (122 views)
Re: 08 f250 diesel no brake pedal Sign In

You can block off the ports of the master and then see if your pedal holds. That will tell you if you have a master issue.





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f250brakeproblem
New User

Jun 5, 2018, 9:53 AM

Post #3 of 10 (120 views)
Re: 08 f250 diesel no brake pedal Sign In

thank you i will try that and get back to you. have you heard of un plugging the abs module or check valves?

thanks again


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Jun 5, 2018, 10:15 AM

Post #4 of 10 (115 views)
Re: 08 f250 diesel no brake pedal Sign In

 Do you mean electrically disconnecting them? Is the ABS light on?





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


f250brakeproblem
New User

Jun 5, 2018, 10:36 AM

Post #5 of 10 (112 views)
Re: 08 f250 diesel no brake pedal Sign In

yes i mean electrically unplugging the abs module? i am going to try your test on the master cylinder first. the abs light is on but i found a broken off sensor uppon my initial inspection so i assumed that to be the reason for the light. i am going to be replacing that also and i will let you know if the light goes off. thanks again for your help.


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Jun 5, 2018, 11:51 AM

Post #6 of 10 (106 views)
Re: 08 f250 diesel no brake pedal Sign In

? There MAY be just a fuse to pull, light will come on and brakes default to regular brakes. If so or it light it on and works (check that too) and problem goes away the unit has a problem if not that's opposite of air in the system but all bets off would professionally bleed it with new exact right brake fluid for it.


One other and just a question? Do the diesels use vacuum for power assist or hydraulic assist? That may change what to look for if not warnings or no codes?


T



Hammer Time
Ultimate Carjunky / Moderator
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Jun 5, 2018, 1:21 PM

Post #7 of 10 (100 views)
Re: 08 f250 diesel no brake pedal Sign In

It probably has an external vacuum pump for the brake assist but the symptoms don't point to a booster issue.

Plugging off the master is a good test but it's easier said than done. It takes a special plug with a flare seat. You can't just go screwing any kind of plug in there.
Also once you disconnect those lines the master will have to be bled to remove the air you just allowed in.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



f250brakeproblem
New User

Jun 5, 2018, 3:00 PM

Post #8 of 10 (88 views)
Re: 08 f250 diesel no brake pedal Sign In

my brother and i are mechanics but dont feel like spending extra money on parts that do not need to be replaced. the diesel is a hydraulic assist as they do not create enough vacuum the system does not have air in it as there is no leaks...... and my fluid level has not changed and my boost comes from the power steering pump system. im aware that i have to bleed the master after running the test that i would like to prove that is not the problem. im just posting on here looking for someone who may have an easier solution or a definitive way of testing the system without trial and error parts replacement at the tune of $$$$$ also as i previously indicated in the origionn description the problem was intermittent then changed to a full blown failure again proving its not air in the system. thanks again for everyone offering advice and opinions its much apreciated.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jun 5, 2018, 3:25 PM

Post #9 of 10 (86 views)
Re: 08 f250 diesel no brake pedal Sign In

If you are getting a sinking pedal while holding steady pressure and you are not losing any fluid, then it's either a master or the ABS hydraulic unit and plugging off the master is about the only way to isolate which one. If you just can't get a solid pedal even temporarily, then you may have air in the system or a bad master.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Jun 5, 2018, 11:26 PM

Post #10 of 10 (70 views)
Re: 08 f250 diesel no brake pedal Sign In

Plugs for a master without spending a fortune: Can make those with short brake line, pre-made cut, bend hard with line braze to seal if needed. If no air it should feel solid at your pedal. If those are pre made I just never bothered. I can't buy just the flare nuts for the cost of those short lines whole + save the one you don't use.
Easy on throwing parts at it never mind if you can afford it you want to really know why it needs what and not have defective or improperly installed new stuff to confuse the diagnosis for the final fix,


Tom







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