Hello all...driving my truck this weekend and too my surprise the brake warning lamp on the dash came on. No noticeable difference in pedal feel or braking performance. Pulled all the wheels today, serviced all the brakes, no leaks visible...fluid level and condition ok. I am thinking the prop valve switch has failed. Any thoughts?
Thanks
Brent

 

The actuating pin moved over enough to engage the circuit... reset it by removing the switch, cracking a front and rear bleeder, and manually reaching in with a small screwdriver until the light goes out.... gotta gently bleed the system so it does not engage again. ..

But ya might as well get the 10 dollar tool to lock it in place.

 

I didn't try that today..I did move the pin. Moved easily with my fingers...

 

If you're talking about the pin sticking out the front end of the valve assembly, that won't have anything to do with the pressure differential valve spool. That pin is for use when bleeding out the front brake circuit. It goes to the metering (hold-off) valve. HIO is talking about the pin on the under side of the brake warning light switch sticking up out of the valve body.

You didn't mention what model or series your truck is: F100, F150 F250 of F350 and if it's 2WD or 4WD (?). Depending on what series and GVW of the truck will determine what valve type you have. If it's an F100-F250 with a GVW of under 6900#, the valve will be cast iron and was made by Kelsey-Hayes. If it's an F250/F350 with a GVW of 6900# or greater, the valve would be brass and was produced by Weatherhead.

Either Dentside disc/drum valve is more than just a proportioning valve. There's the metering valve to control the front brake circuit, pressure differential sensing valve between the front and rear circuits and there's the proportioning valve to control the rear brake circuit, all within the valve body assembly. Proportioning is only 1/3rd of the valves total functions.

This is the drum/drum pressure differential valve for a Bumpside. It doesn't have any metering or proportioning functions but, it shows you the basic operation of how the pressure differential valve circuit would also work in the Dentside disc/drum brake valve.




Kelsey-Hayes cast iron disc/drum brake valve.




Weatherhead brass disc/drum brake valve.

 

To hopefully go with what he said.

 

Great, thanks for the info guys. I'll try that tonight
cheers
Brent

 

OP's "About Me" profile: 1979 F150.

D5TZ-2B257-B .. Brake Pressure Differential Valve / Marked: D5TA-2B524-FA or FB / Obsolete

1975/79 E100/150 & F100/150 2WD/4WD & F250 2WD with 6,200 lbs. GVWR; 1976/79 F250 4WD & Bronco; 1979 F350 4WD
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C8AZ-2B264-A .. Brake Pressure Differential Valve Warning Lamp Switch / Obsolete ~ Available NOS & from auto parts stores.

1968/69 all FoMoCo Passenger Cars; 1968/79 F100/350, Bronco & Econoline.

 

Thanks number dummy ..checked everything..pulled the switch out. It has continuity all the time regardless of pin position.
I still think switch has failed....

 

Scratch that...looking in with a mirror...the valve looks off center...bleeding didn't help. Guess 8ts stuck

 

Follow the procedure for centralizing the pressure differential valve in post #5. You'll just have to determine which way the valve shifted in order to open the opposite brake circuit to push the spool back to center.

 

No luck centering the valve. Its my daily driver so I didn't want to pull it off and take it apart. Found a replacement from bronco graveyard, when it arrives i'll dig into it. want to get my fitech installed first lol