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Tech501
Tech501, Auto Service Technician
Category: Car
Satisfied Customers: 747
Experience:  38 years exp, ASE Mastertech with L1 Advanced Engine performance
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1990 F250: petal..diesel truck..truck parked and running..pedal down

Customer Question

The brake petal went down on my 1990 F250 diesel truck and I lost brakes. With the truck parked and running when you push the pedal down it stops about half way down for about 3 seconds like you have brakes then it goes all the way down. I though it was low of fluid but I checked it and it was actully running over. I though sure it was the master cyl. so I replaced it and it still does the very same thing. WHAT IS WRONG WITH IT???
Submitted: 11 years ago.
Category: Car
Expert:  DCM replied 11 years ago.
Does your brake fluid ever go low in fluids?
Expert:  Tech501 replied 11 years ago.

Your problem is what we call a "dump valve". It's an ABS release valve and it is bypassing. In the illustration below, it's located under the truck and is called an Electro hydraulic brake proportioning valve.











Customer: replied 11 years ago.
Reply to DCM's Post: NO it dose not go low, when this problem happened it actully overflowed.
Jsmith
Customer: replied 11 years ago.
Just read your reply and wondered whaat is the fix for it? Is it repaarible or must it be replaced?
Jsmith
Expert:  Tech501 replied 11 years ago.
It must be replaced. I expect you would be able to find a remanufactured unit.
Customer: replied 11 years ago.
Thanks,
This PM I looked for the valve you mentioned and the only valve I found was one in the rear brake line that only had and inlet and an outlet with no way for fluid to return to master cyl. I bled the brakes real good and I really think the new master cyl. I installed is defective.
Please reply if you have any other ideas.


Jsmith
Expert:  Tech501 replied 11 years ago.

There are only 2 place for fluid to "bypass" without hitting the ground and they are the master cyl and that valve. That valve does vent to the master. That's what it is put there to do, assuming you found the right valve. It has to look like the one in the picture. If I have answered your question sufficiently, please click on the accept button for my answer.


Thank you

Customer: replied 11 years ago.
I checked ever inch of the brake line from the rear brakes to the master cyl. and that is the only valve. The master cyl. only has 2 lines coming out 1 goes to the front brakes and the other to the rear so I see no way for the fluid to return to the master cyl. I plan to check (replace the master cyl.) before I replace a $250.00 valve.
Any other ideas are welcome.

Thanks
Jsmith
Expert:  Tech501 replied 11 years ago.
I don't disagree with that. I've had plenty of bad ones.
Customer: replied 11 years ago.
Reply to Tech501's Post: You said you haveseen plenty of them are you refering to the master cyl. or the dump valve?

Jsmith
Expert:  Tech501 replied 11 years ago.
I was referring to replacement remanufactured master cylinders. Some of them aren't very reliable.
Customer: replied 11 years ago.
When does this dump valve do its dumping? when you are using your brakes or just moving down the road?
I drove it this morning and for 1/2 hour everthing was fine then I hit brakes and it went to the floor like there was no fluid in it but after pumping them for a while they built back up again. Oh I put a new master cyl. on it not a rebuilt.
Some place on this site it said there were 12 replies to this problem but I have been unable to figure out how to access them.
A am sorry for all the trouble but I am just trying yto solve this problem because brakes are very important.
Thanks
Jsmith
Expert:  Tech501 replied 11 years ago.

The "dump valve" is an ABS release valve. When the ABS energizes and releases the rear brakes, that where it releases the pressure.


After the first post and the last, if you see something that says "view all" click on that to see all the responses. You may have it in "simple view" which hides the ones you already read.

Customer: replied 11 years ago.
I tryed simple view and view all but was not able to see any other replys. To me this web site is difficult to navigate.
Your last answer did not clearly answer my question but I took both lines off the master cyl. and put plugs in them and the brake petal did not go down so I am fixing to put the valve on and hope it works. If it does I will ACCEPT.
SMITH

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