Hi everyone:

On the Aerostars, immediately after the Master Cylinder is what they called the Brake Combination Valve (before the RABS valve). Can this valve be disassembled and cleaned? If so, how?

Thanks

 

Copper, I have never heard of anyone cleaning a proportioning valve. Usually it is a replace only item. I could be wrong.

I believe this is more kenmods turf.

 

Thanks Nighthawk. But Kenmod has a nasty habit of taking a vacation when you need him most. I'll bet he's in Hawaii surfing right now while I'm here up to my eyeballs in brake fluid

 

proportioning valve has a vertical pin switch in the center black screw that corrodes and sticks causing RABS failure...i've cleaned the switch and lubed with silicone spray...
on drivers side end of prop valve is a piston held in by end cap under internal coil spring pressure...careful when removing cap...spring flys...piston can be cleaned...cap has neoprene plug in end which can be damaged and leak...
small chambers for debris and water to settle out and cause problems...

easy to flush via line fitting

 

Thanks 96_4wdr:

When I open up the driver's end you are talking about, it's so corroded the spring took a lot of coaxing to come out. The neoprene seal seems to be intact. Now, the million dollar question is the neoprene seal. It's shaped like a cup. Which way is in?

On second thought, it's only $72 + $9 shipping, so I'll just order it. I looked inside all the bores, and the corrosion is unbelievable. Once I clean off the cruds, the surfaces are full of pits the size of a B-52 bombing run. I'm cheap, but not when it comes to brakes.

 

In most brake parts, such as wheel cylinders, the cup part goes towards the brake fluid. The pressure helps push the cup against the bore so it seals.

 

In the midst of that massive brake issue I had around Thanksgiving, the cuplrit turned out to be the device that generates the pulses to keep the brakes from locking. It sounds very similar to the "proportioning valve has a vertical pin switch in the center black screw that corrodes and sticks causing RABS failure" issue that 96_4wdr is describing. That thing cost me about $160 plus the labor to put it on. That is one job I was glad I farmed out instead of tackling myself.

Regarding brake parts, I'm with Copper. . .that is NOT the place to save a penny on trying to rebuild a questionable part. Seriously, I don't even rebuild wheel cylinders any more. There about $8, and I can't rebuild one for that much in time.

 

the neoprene end plug/seal appears to be a type of semi free floating pin to reposition the proportioning piston or perhaps a end cushion for the piston...the plug/seal goes one way with the tip sticking out thru hole...do not operate valve without the piston in place, high pressure brake fluid will blow out the plug to kindom come....
my problem was with the corrosion on the center switch pin and spring preventing the switch from working...no rebuilding
little to no corrosion in rest of prop. valve...some water/dark slurry brake fluid mix thru out the valve interior
cleaned, flushed and bled....been working great last 6 months

Dave...you are describing the double solenoid RABS valve in the system after the prop. valve

Ford has made several configurations of this and similar RABS systems, some combine the proportioning valve function and RABS pulsing solenoid valve function into one unit

the proportioning valves main function is to supply only a percentage of the total brake fluid pressure to the back drum brakes, disc brakes require higher fluid pressure than drum and want less braking in lightly loaded back end during weight transfer braking.

 

Thanks for the info, 96. My trouble is that my one-sentence dsescription of it was the extent of my knowledge of the thing. I keep wishing I was a better mechanic. I really do like my Aerostars.

I also appreciate all the kind assistance I have found on this forum.

I (and several of the guys on here) thought my problem was a bad master cylinder. I replaced that, and did the whole brake job (pads, shoes, turned rotors and drums, new calipers and wheel cylinders, etc.) figuring that approaching 200,000 miles, it might be good PM. None of this really helped the situation. I could stop the van, toss myself into the windshield, lock up the seat belts, and make the tires squeal. Still, If I stopped and kept pressure on the pedal, it would sink slowly to the floor, at which time the red BRAKE warning light and the AMBER ABS lights would come on and stay on until I turned the ignition off and back on.

 

I am sorry, I will try to do better.

Ken

 

Hi Ken:

How're you doing my friend? Back from vacation?

 

That is correct. When it failed, I think it did something to the proportioning valve. Replacing the double solenoid thing didn't solve the issue to my satisfaction, so I replaced that too, and the master cylinder. At 200K miles, I didn't want to take a chance and find out the hard way.

I can truthfully say that was the most frustrating andf difficult diagnosis in which I have ever been involved.

 

Just some food for thought, the only backup in case your brakes go is the E-Brake, so make sure it stays in good working order.