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Hey guys,
Still working on disc brake swap from '78 to '68.
The combo valve off of the parts truck ('78) looks like this one...
I check the pressure differential switch with a multi-meter and found that I have continuity, so that tells me that the internal piston needs to be re-centered.
I would love to re-center it now while I have it on my work bench... plus I'd like to avoid re-centering it by bleeding because I don't know which way it is shifted.
Can I just unscrew the fitting below the bleeder button (see blue arrow) and get to the internal piston that way?
Also, the little rubber cap on the bleeder button is in pretty rough shape, but it doesn't seem to be actually sealing anything... To me, it doesn't look like it will be a problem...can someone who knows more about these combo valves confirm that?... or warn me if you think it will be a problem?
The cast iron valve you have was made by Kelsey-Hayes for trucks with a GVW of under 6,800 lbs. When bleeding the brakes with that style valve, the metering valve pin is pulled outward. (the pin on a brass Weatherhead brake valve, for trucks with a GVW of 6,800 lbs and higher., is pushed inward).
The dust boot on the metering valve pin is usually long gone and I don't know of anyone that supplies them. It will work without it since it isn't a sealing device.
As to pulling the valve apart; It may be risky to do so since there are no seals reproduced for the metering section of that valve, if the seals get damaged while disassembling it.
Most often the pressure differential valve spool is shifted towards the secondary side circuit, since this is the first circuit a person would begin bleeding out when servicing or replacing brake components that requires opening up the hydraulic system.
If it shifted because of an actual brake component failure, then it's hard to say if the spool moved to the primary side or if it moved to the secondary side.
The dust boot on the metering valve pin is usually long gone and I don't know of anyone that supplies them. It will work without it since it isn't a sealing device.
Cool... I thought it looked that way.
Originally Posted by ultraranger
As to pulling the valve apart; It may be risky to do so since there are no seals reproduced for the metering section of that valve, if the seals get damaged while disassembling it.
So, I guess my best option is to install it and try to re-center it by bleeding?
Originally Posted by ultraranger
Most often the pressure differential valve spool is shifted towards the secondary side circuit, since this is the first circuit a person would begin bleeding out when servicing or replacing brake components that requires opening up the hydraulic system.
Makes sense.
I'm starting to wonder if I should just buy a new combo valve and not fool with this one. Ultra, you used a bullnose combo valve, correct? Was it new or a junkyard valve? If new, where did you purchase it?
Or should I just try to re-center the one I have?
Thanks, as always, for your help. You certainly know your stuff, especially when it comes to brakes.
The brake valve I have was an OEM/NOS item that was still in the Ford logo box when I got it. I purchased it off of Ebay. It was for an '84-'86 F150/Bronco. E4TZ-2B257-B.
I found this one that is supposed to be a direct replacement for 76-86 F-Series trucks.
The price seems reasonable, but I'm a little concerned by the line that says, "For dual wire brakes switch, wire both wires to the single new pigtail."
Wouldn't that cause the brake warning light to be on all the time????
It's a reproduction valve that was originally designed for GM vehicles. It's SIMILAR to the valves that were made for Fords.
The '67 model Fords were the only ones that had a one wire pressure differential switch. From '68 and beyond, the switch had two wires.
One of the two wires went back to the prove out contact on the ignition switch. When you turned the key to the Start position, the brake warning light would come on for a moment until you moved the key to the Run position. That let the driver know the brake system was normal and that the warning bulb was good. --if the warning light remains on when the ignition switch is in the Run position, then the brake system needs some immediate attention.
Even though there are two wires on the '68-up pressure differential switch, the contacts are tied together (the two prongs on the switch are electrically at the same potential) as seen by the metal bar that links the two prongs together here.
1984/89 F150 & Bronco: E4TZ-2B257-F / See parts catalog pic for E4TZ-2B257-B applications.
Perhaps it's possible I've misquoted the number since I was trying to recall from memory what was on the Ford box the valve came in. It could have been an F and not a B. I had installed the valve on my truck nearly two years ago now and the box is no longer lying around.
Well, now you're making me re-think whether or not my valve actually is out of center or not... I thought that it was because I had continuity across the wires, but if they're tied together then they will always have continuity. Is there a way to bench-test it?
Well, now you're making me re-think whether or not my valve actually is out of center or not... I thought that it was because I had continuity across the wires, but if they're tied together then they will always have continuity. Is there a way to bench-test it?
To test the valve, you don't read across the pins. Put one meter lead on the contact pin on the switch (doesn't matter which pin --they're tied together). Touch the other meter lead to the outside (body) of the brake valve. If you have no continuity showing on the meter, the pressure differential valve spool is centered (things are good).
If you do have continuity, the spool is shifted off-center.
The circuit is looking for a path to ground through the body of the valve itself. As long as the spool isn't shifted, there will be no electrical path to ground (the circuit will be open) and the warning light will remain off.
To test the valve, you don't read across the pins. Put one meter lead on the contact pin on the switch (doesn't matter which pin --they're tied together). Touch the other meter lead to the outside (body) of the brake valve. If you have no continuity showing on the meter, the pressure differential valve spool is centered (things are good).
If you do have continuity, the spool is shifted off-center.
The circuit is looking for a path to ground through the body of the valve itself. As long as the spool isn't shifted, there will be no electrical path to ground (the circuit will be open) and the warning light will remain off.
Hey Steve. I totally believe your test method here but I am surprised it works. I would have thought the o-ring seals on either end of the spool would have isolated it from the body of the valve. Therefore not allowing an electrical path even if it is shifted. What am I missing?
Hey Steve. I totally believe your test method here but I am surprised it works. I would have thought the o-ring seals on either end of the spool would have isolated it from the body of the valve. Therefore not allowing an electrical path even if it is shifted. What am I missing?
Ok, if you really want to know, look at the pin on the ends of the valve spool. If the spool shifts over, the pin comes in contact with the body of the brake valve.
The current path comes from the wires attached to the switch. The plunger on the switch is metal and is in contact with the valve spool. The spool, if shifted, touches the body of the valve. The valve is mounted to a steel bracket that's attached to the frame/chassis of the vehicle and thus completes the electrical path back to the battery and turns the warning light on in the process.
This is a pressure differential valve only but, it clearly shows how the spool operates.
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