Brake Proportioning Valve

90scgreyghost

Registered User
I have a 1990 SC that needs a proportionig valve for the ABS braking system. Not sure if it needs the switch, but the mechanic mentioned the possibility. The mechanic had a line on a new/rebuilt one, but it fell through. So I'm looking for used or new...
 
Are you talking about the part that goes on the frame just below the master cylinder? :confused:

I have some of those.....

What problems are you having with your ABS system....
 
That's the one... I have a 1990 SC with 189K. I had a new engine put in and a new master cylinder 4 years ago. Haven't got it runnig right since then. Finally found someone willing to put the time in and who is really knowledgeable about SC's. He replaced the rear brake calipers because they had gone bad from sitting, and needed to replace the proportioning valve under the MC. He had a line on one from a dealership , but it fell through, So I did find a new one on the Team Ford site thanks to RickTBird for $78. I haven't purchased it yet so...

Jerome
 
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I have one from an 89 SC....

Give me your zip code and I'll quote you a price that includes shipping....
 
Note that the block isn't really a proportioning valve. It is just a junction block that has the pressure sensor for the suspension control system in it. That doesn't make replacing it any easier, but just a note that there is nothing mechanical in it.
 
Does anyone have a part number for a junction block WITHOUT the ARC sensor port?

For those of us disabling ARC?

RwP
 
Note that the block isn't really a proportioning valve. It is just a junction block that has the pressure sensor for the suspension control system in it. That doesn't make replacing it any easier, but just a note that there is nothing mechanical in it.

That would not be entirely correct. That is the proportioning valve and it also contains the pressure switch for the ARC. You can remove the sensor and plug it off. I believe it is 1/8" pipe thread but I'm not entirely sure. I've plugged it before but can't remember for sure on the thread. All the sensor does is engage the ARC under hard braking. On the 89-92 SC it is important to retain the actual proportioning valve for proper braking balance.
 
I believe it is 1/8" pipe thread but I'm not entirely sure.

It may be 1/8" thread, but it's not pipe. It's straight thread and requires an o-ring to seal. I know I tried a pipe plug on mine when i was trying to seal it and it still would leak when staging at the line.

hmm, I thought the proportioning for the front rear bias was handled in the master cylinder on the 89-92.
 
That is the proportioning valve and it also contains the pressure switch for the ARC.
:confused: Ummm... dave.. Are you sure about that? I've read in the service manual that the proportioning of brake fluid pressure is handled by the Teves II ABS unit itself. That junction block there is just a Tee for the ARC pressure switch. With just 1 line in/out, there is no pressure differential in the block, so I don't understand how it could control 2 different pressures. The only thing that I could see would be a orifice, but that would only provide a minimum amount of damping and there's not a significant amount of fluid movement in the rear brake lines.
 
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You are right, it's not 1/8th pipe. I recall now that I welded the switch solid and screwed it back in. LX's with ABS have the same valve but without the switch. Maybe they are still available?

And yes I am damn sure it's a proportioning valve. Look it up if you don't believe me. :)
 
Alldata indicates that it is what is called a "combination valve" providing proportioning and a port for a warning sensor. This follows through for my 1990 and 1993 though no part number is available. I don't doubt Dave is correct.

found my old thread. A 3/8" fine thread bolt will thread into the port if the problem is fluid leaking past the body of the switch housing. But it won't seal without an o-ring. I spent a day getting various o-ringed hydraulic plugs at the local tractor service shop and never found one that fit.

In the end you can buy a replacement switch. Rockauto lists it as a Power Steering pressure switch available from Standard Motors #PSS18 for around $80.00. At one time I checked into aftermarket replacements. At that time the switch was over $100. There are a couple standard hydraulic pressure switches you could use to replace this one, but they all were more than $150.

Be careful when changing that as all the brake fluid in the master can get sucked out pretty fast. You'll want someone topping it off as you work, otherwise prepare to bleed the brakes.
 
Quoting one (1990) factory manual...

Brake Control Valve and Pressure Switch

The brake control valve assembly contains a proportioning valve in an aluminum body and a pressure switch.

Proportioning Valve

The proportioning valve regulates the hydraulic pressure in the rear brake system. It is located between the rear brake system's inlet and outlet point in the control valve. (see attached for more w/diagram)
 

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