How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask DEALERTECH37 Your Own Question
DEALERTECH37, Technician
Category: Heavy Equipment
Satisfied Customers: 92
Experience:  CAT, Cummins, Detroit, other
Type Your Heavy Equipment Question Here...
DEALERTECH37 is online now
A new question is answered every 9 seconds

I have a ford F-750, It has air brakes when I set my parking

This answer was rated:

I have a ford F-750, It has air brakes when I set my parking brake it dumps all my air down to 0 psi I have checked the lines and cleaned the valve in the back by the brakes and checked each of the air cans all seemes to be in order any suggestions?

HI there. Welcome to JA. I'm KC. I'm here to help you if I can.. OK now, where is it dumping the air out exactly?Let me know.. thanx..KC

Customer: replied 8 years ago.
The Air is dumping out at a valve right near the back brakes, it has a dump port in it, and three lines are hooked to it one ias a main air line one goes to the brakes and the other I'm not sure.
Ok now, that is the quick release valve. Has that ever been replaced?
Customer: replied 8 years ago.
No, Not replaced but I did remove it and pulled it apart. It was a little gummed up but I cleaned it up and checked the O ring in it and made sure it was sliding good and put it back together. I could blow in it and hear the slide woking in it. Another thing, when I let the system charge it works good the brakes function and stay charged, its only when I apply the parking brake that it dump.

so you still have the original complaint that you were trying to repair? No lines have been crossed or anything? Just double great running and released, brakes are functioning normally? only dumps it out there? Is the lines going to chamber on parking or service side/..Try plugging brake hoses to chambers with visegrips and a rag, see what happens...

Customer: replied 8 years ago.
Same complaint, No lines crossed, only dumps out at the valve,the line from the quick release valve goes to the service side. I tried the vice grip trick on both sides of the brakes there was no change.
Ok , there should be a small 1/4 or 3/8 line going to the valve coming from the front of the truck, that should have air on it when park released...and the other main line going to air supply from tank??
Customer: replied 8 years ago.
OK I traced the one to the tank then I found the 1/4" line cracked it open with the system charged and pressured air came out.
Ok air entering the valve at the top supply port is suppose to seal off the exhaust port and at the same time, it allows air out the delivery ports., then it balanxes out..
Customer: replied 8 years ago.
So does it sound like my valve is bad?
Yeah it sure sounds like it, when you take the air away it is supposed to seal off the exhaust as well, it sounds like yours isnt actuating right inside. Is this just a little valve 3 port right?
Customer: replied 8 years ago.
yea, it has optional ports but only three are actually active.
how big is this valve? iwanna make sure we have the right valve..
Customer: replied 8 years ago.
It pretty much fits in the palm of you hand, probably 31/2" in circumfrance
Thats the one, it is usually mounted on the axle midway between the 2 actuators connected to it...Hope this helps
DEALERTECH37 and other Heavy Equipment Specialists are ready to help you
Customer: replied 8 years ago.

I hope so too, I will pick one up tomm. You been very helpful . I really don't know what it would be if it's not that.



if any probs,,,please get back with me and let me know, we'll get it...Thank you very much...KC