I have a 1974 F250 4x4 with Power Drum Front & Rear Dana 60's.

The Brake light stays on. IIRC, the book says that the light is related only to the Portportionate Valve (PV) and not the emergency brake. Due to loss of fluid, the PV cylinder slides to one side and blocks the leaking side, thus turning the warning light on. To fix the problem, bleed the brakes after fixing the leak and it should center it self. I did that a couple of times and it still stays on.

I checked around and the only leak maybe coming from the Master cyl cover, it weeps. I haven't pulled the drums off to inspect the Wheel cyl and it will be the last resort if I do.

The PO said he believes the light came on because one side of the MC was very low. It hasn't gone low since I've owned it.

The truck stops find, no soft pedal.

I notice that the MC has been changed some time ago, it has a few adapters on the incoming brake lines. It also has a large reservoir and a small one. I thought that type is used only for disc brakes. Do I have the correct one and should I change it if I do.

I've had this same problem with my 69 Mustang. The PV cylinder valve rusted inside and had to be rebuilt. I see no rebuilding kits and I can't locate a replacement.

What should I do?

Thank you!

 

Any thoughts?

 

Correct the 'brakes" dash light is a warning light for a brake system leak/failure ONLY. Do you have drums all the way around?

The front MS area is suppose to be bigger, it is for the front brakes, so you are ok there. The elec connector on the pro valve is notorious for being bad, so says FTE folks.

When you bled the brakes did you pull or push the pin on the end if the pro valve?

Some books say during bleeding you need to either hold out or push in. And some say do it after wards...also some sources say the pins direction is based off the GVWR?

 

Has drums front and back
GVWR = 7700
Never knew it had a bleeder valve. That is something new to me????

It looks like if your using the bleeder valve tool, then they want the pin pulled out?

Where to pick up that tool. IIRC, Haynes manual doesn't make reference to it.

So, if I was to bleed the system again. I need to have the valve pulled????
I assume that it will allow the Sliding Caliper to center itself and the light should go off.

Right now, All brakes work with the light on.

If I had a mechanical not an electrical problem and the sliding caliper went to one end, would that shut off pressure to the other 2 wheels?????????

Thank you for your time and help!

 

See 1st pic, I believe it is called a "bleeder rod" on the "metering valve". You can make the hold out tool by bending a piece of sheet metal in a U, but 1st cut or grind a V in it. The pin SHOULD only come out like 1 or 2 16th's of an inch.

It is a sliding piston (pressure differential valve) inside there. Since the brakes are working I would make sure it is not just a electrical connection issue, they are known to go bad or be a problem (indicate a false problem) even when the brakes are fine.

I have also heard that after bleeding the brakes, sometimes you have to stomp the brake pedal to dislodge a stuck piston????

Get on line and look up a Chilton manual.... they are about as good as a Hanes book, but I think it is in there??

 

Got it, Good information!!!

What about the possibility of an electrical problem?
What procedure do you suggest to determine if there is something wrong with the sensor?
Thank you for your help,
John

 

If I remember right Number Dummy always says or has said that the elec connection can be a problem. Corrosion and or the plastic housing getting brittle and cracking, there fore making for a bad connection can cause problems.

https://www.ford-trucks.com/forums/1...ing-valve.html

Ford Truck Enthusiasts Forums - Search Results

 

Too cold in the garage to do any work, but I was able to get a picture of my PV.

As you can see there is no relief or bleeder valve. The backside is smooth.
Is it because I have drums all around?

So, does the above principle still apply?

To test the sensor. Do I use a test light and touch the clip on part at both terminals? What am I expecting?
How do I test the sensor itself?

 

Here is a very informative thread.

https://www.ford-trucks.com/forums/1...atibility.html

To test the sensor: You should be able to disconnect the wire's connector from the valve (I think it's white/purple but don't remember for certain) and ground it, that should make the dash light come on (with the key on).

The electrical switch in the valve merely grounds that (those) wires when it feels the need; if all is well with the electrical connections and wiring, the dash light will come on.

Much of Ford's circuit wiring in this era works by completing a ground connection, not by supplying "positive" current.

https://www.ford-trucks.com/forums/1...lve-issue.html