Hello, I would appreciate any help. I'm trying to find a new proportioning valve for my 81 F100 stepside. (It has 11" discs and 11 inch drums). It must have some gunk in it because I'm getting very little brake pressure to the rears, and the master cyl is leaking internally from the rear brake reservoir. The local parts stores don't seem to have a listing for any 81 F100.

Three questions:
1. Will a proportioning valve from a 76-79 F150/Bronco work? (I did see one of these on the shelf and it certainly looks the same from the outside).
2. What other years will work and does anyone have one for sale?
3. Can they be taken apart and cleaned/rebuilt?

Any help would be appreciated.
Thanks!
John
http://i135.photobucket.com/albums/q...h_IMG00252.jpg

 

If the master cyl is bad, I'd just replace it and see what happens. Proportioning valves rarely go bad

 

I already replaced that, and it didn't change the condition. Thanks for the reply.

John

 

Welcome to FTE

EOTZ2B257A .. Brake Differential Proportioning Valve / Obsolete

Fits: 1980/83 F100/150 & Bronco / 1980/83 F250 = under 8500 lbs. GVW.

Sorry....No Ford dealer or obsolete parts vendor has any.

 

post more details... I really doubt your proportioning valve is clogged. Have you tried flushing brake fluid through it?

 

the brakes have never worked quite right since I've had the truck. at first, the front calipers were not releasing. I decided to replace everything at all 4 wheels (rotors, calipers, pads, wheel cyls, shoes, & hardware) and after that a new mc & booster. when I was removing the fronts I made the mistake of compressing the pistons instead of just draining the old fluid. that sent quite a bit of rusty gunk back up into the prop valve & mc. when I got it all back together I couldn't get a proper bleed at the rear since there wasn't enough fluid flow. now i've got fluid leaking past the mc cover seal, and I can see the over-pressure port functioning back into the rear brake reservoir. (same thing was happening with the old mc also). all of this leads me to believe that the prop valve is clogged to the rear brakes, or the piston won't center properly in the prop valve.

i drove it today for the first time in the snow and it was quite a ride with only the fronts trying to stop the truck, and the rears just kept spinning on the ice/snow. even with the pedal to the floor the rear brake pressure wasn't enough to stop them from rotating at idle in drive.

if you have any other ideas I like to hear them.

anyone have an extra prop valve for sale from a 80-83 F100 or F150 or F250 (under 8700)?

John

 

If you can't find one, you could get rid of it. It just delays the rear brakes from coming on during a panic stop to keep them from skidding. Each valve is calibrated for the type of vehicle it goes in, so a Bronco won't work correctly. Another from a truck that closes matches yours in length and weight would probably work good enough.

You could also just take it out, and install a manually adjustable aftermarket valve in the rear line. They sell them at summit racing. Race cars use them all the time to balance the rear to front braking.

Here's one. You made need some adapters for the lines.
http://store.summitracing.com/partde...5&autoview=sku

Here's another that might have a simpler hookup.
http://store.summitracing.com/partde...5&autoview=sku

 

I agree with that. Also, I can't see how compressing the caliper pistons would introduce gunk in the system, it just pushes fluid to the master cylider.

 

In a disc/drum brake setup the proportioning valve is quite important and should be replaced with a working as soon as possible. At least you can pull it apart and give it a clean fairly easily and see if the dividing piston is seized. If the piston is seized covering one of the ports then there's not much that can be done, but if it's seized in the middle you can still use it as a proportioning valve, you just lose the safety feature of it.

Now I'm not sure if the F100 one does all of this, but here's some of the functions the prop valve might perform:

1. Drum brakes and disc brakes require different amounts of force (line pressure) to activate them. Due to the drum brake shoe's leading edge 'digging into' the drum it requires less force to make it work which is why (most) drum systems do not need to use a vacuum booster. The proportioning valve provides a lower pressure to the rear lines, otherwise they will tend to lock first (which is very bad!).

2. The proportioning valve may also be used to hold residual pressure in the rear line to prevent the springs inside the rear drum from pulling the shoes too far away from the drum. If the shoes get too far away from the drum you will have to pump the brakes to get a solid pedal every time you go to stop. Disc brakes have no active measure (springs) to push the pistons back in the calipers, they rely on sloppiness in the bearings and an allowable disc 'runout' to release brake pressure on the disc. They don't need residual line pressure to prevent the pads moving too far away from the disc.

3. The proportioning valve usually also contains a piston separating the front and rear brake circuits. If for whatever reason one of the circuits has a catastrophic failure, the high pressure from the good circuit will push the piston to the 'bad' side and it will block off the outlet. This keeps the master cylinder from draining completely and leaves you with at least some braking ability.

4. It may also be used to provide a delay to the front brakes to let the rear ones come on first, but I think this is taken care of in the master cylinder in the F100

If the earlier F100's had identical brakes to yours you should be able to use one of their valves. Maybe the mounting is different. These guys might be of some assistance Proportioning Valves

 

1980/89 Ford Light Truck Parts Catalog / Brake Section 22, page 3.

EOTZ2B257A: 1980/83 F/U100/250 under 8500 lbs. GVW

This is the only valve listed for a 1980/83 F100.

This is the only valve listed for a 1980/83 F150.

This is the only valve listed for a 1980/83 U150 = BRONCO.

This in one of two valves listed for an F250.
``````````````````````````````````````
1984/86 Bronco uses the same valve an F150 2WD/4WD does: E4TZ2B257B

1976/79 Bronco uses the same valve a 1975/79 F100/250 2WD/4WD does: D5TZ2B257B

 

Well that goes to show, it's function is not that critical.



2. The proportioning valve may also be used to hold residual pressure in the rear line to prevent the springs inside the rear drum from pulling the shoes too far away from the drum. If the shoes get too far away from the drum you will have to pump the brakes to get a solid pedal every time you go to stop. Disc brakes have no active measure (springs) to push the pistons back in the calipers, they rely on sloppiness in the bearings and an allowable disc 'runout' to release brake pressure on the disc. They don't need residual line pressure to prevent the pads moving too far away from the disc.
I disagree with this. Mis-adjusted shoes are the #1 cause of a low brake pedal. Residual valves, if any are used are mounted in the mastercylinder port, and their only purpose is to keep the cup seals out against the wheel cylinder bore.



3. The proportioning valve usually also contains a piston separating the front and rear brake circuits. If for whatever reason one of the circuits has a catastrophic failure, the high pressure from the good circuit will push the piston to the 'bad' side and it will block off the outlet. This keeps the master cylinder from draining completely and leaves you with at least some braking ability.
I disagree. There is a piston in the proportioning valve separating the two circuits, but it's only purpose is to turn the "brake" dash light on. Ask anyone who lives in a area were they spread salt on the roads, when the rear line rusts and springs a leak, you will lose ALL of the brake fluid in the rear resevoir of the mastercylinder.



4. It may also be used to provide a delay to the front brakes to let the rear ones come on first, but I think this is taken care of in the master cylinder in the F100
I have heard of this before, and cannot say whether it does this or not. Some people think the rear needs to "lead" the front to provide straight braking. All I know is the rear locking up during a panic stop will make the rearend come around, and you will end up pointed in the opposite direction you were originally headed.

 

I'm with Franklin2 on the residual pressure to keep the shoes from retracting too far. Thats what the adjuster does, the shoes retract all the way to the anchor pin The proportioning valve will stop flow in case of a blown line etc though

 

Have you traced the steel brake line to the rear of the vehicle to check for dents or damage? Also, it's possible for the a brake hose to collapse internally while looking fine on the outside. Check that you've got good flow to and through the brake hose and lines....they're much more likely culprits than a proportioning valve.