Fordnatics List Archive

This read-only message was archived from a public mail list.
Mail From: (email redacted)

I am trying to set the brake proportioning valve on my 1986 5.0
liter Mustang. Others have suggested that I make this adjustment
using "trial and error".

Well, I have tried just that. I've turned it all the way one
direction and then the other, at about one turn at a time. Each
time I tested the brakes at about 30 to 40 mph. The front
brakes ALWAYS lock up first.

The valve has arrows indicating increase or decrease. My question
is, increase or decrease what? Does turning the valve in the
increase direction increase braking on the rear or front brakes?

What is the correct hydraulic schematic for the brake proportioning
valve? Maybe it isn't connected correctly.....

Please send your responses to:

(email redacted)

Thanks in advance,
(email redacted)

This read-only message was archived from a public mail list.
Mail From: "WHITET.ACIOMAHA" </S=WHITET.ACIOMAHA/O=apcom/PRMD=apcom.oma/@sprint.com>

Original To (Oracle): OFFX400:C=US;A=TELEMAIL;P=INTERNET;D-RFC-822=(email redacted)
Original CC (Oracle): Ford

>I am trying to set the brake proportioning valve on my 1986 5.0
>liter Mustang. Others have suggested that I make this adjustment
>using "trial and error".

Unfortunately, there is no magical setting.

>Well, I have tried just that. I've turned it all the way one
>direction and then the other, at about one turn at a time. Each
>time I tested the brakes at about 30 to 40 mph. The front
>brakes ALWAYS lock up first.

Can you feel any difference in the rear? Did you modify or replace
the stock proportioning/cutoff block so it will only cutoff a ruptured
line?

>The valve has arrows indicating increase or decrease. My question
>is, increase or decrease what? Does turning the valve in the
>increase direction increase braking on the rear or front brakes?

The proportioning valve really is a restrictor valve. You are increasing
or decreasing the flow to the rear brakes. If you didn't modify the
stock proportioning/cutoff block, you are restricting the flow in two
places and you will never be able lock up the rear brakes. IMHO, I
wouldn't remove the cutoff block in a street driven car, I would either
modify the stock one or purchase the Motorsport item.

>What is the correct hydraulic schematic for the brake proportioning
>valve? Maybe it isn't connected correctly.....

The proportioning valve can be placed anywhere in the rear brake line
after the stock cutoff block (should no longer perform the
proportioning) and the T fitting at the rear axle. As I said before, the
proportioning valve really just restricts the flow to the rear brakes.
On a street driven car that autocrosses or sees limited track time,
I like to place the proportioning valve in the engine compartment. Ford
was kind enough to put a fitting in the rear brake line that can be
removed and the valve can be inserted there. It is important to make
sure the valve is securely mounted as the brake line is only going to
take so much stress of the valve bouncing up and down.

Tim White
#81 AS Mustang

This read-only message was archived from a public mail list.
Mail From: (email redacted) (Dave Williams)


-> Well, I have tried just that. I've turned it all the way one
-> direction and then the other, at about one turn at a time. Each time
-> I tested the brakes at about 30 to 40 mph. The front
-> brakes ALWAYS lock up first.

You're another victim of false advertising.

Add-on "proportioning valves" don't proportion anything. They're just
pressure limiters. If your rear wheels lock up first, you can put the
valve in and adjust it to where they don't. However, if the front
wheels lock up first, there's nothing you can do about it. Well, you
could put the valve in the line to the front brakes, but that would be a
generally bad idea.

I assume your car has drum brakes in back.

You might be able to find some high-CF brake shoes, but your most
reasonable approach is to find some wheel cylinders with a larger
internal bore, giving you more force at the rear brakes. A Mitchell
service manual would give you the bore diameters for various Ford
products, and then you could annoy your favorite parts place matching up
wheel cylinders. When we were racing a GM car, we found most GM wheel
cylinders would interchange, and could select bore sizes from 5/8 to
1-1/16.

One thing you need to be careful of is, drum brakes are sensitive to
the speed you apply the pedal. You might not be able to lock the wheels
with a slow push, but jab the pedal and you might lock them easily,
depending on the way Ford built the lever ratios.

If you have rear discs, you can select high-CF pads to adjust the brake
bias.

==(email redacted)=========================DoD# 978=======

This read-only message was archived from a public mail list.
Mail From: (email redacted) (Dave Williams)


-> The proportioning valve can be placed anywhere in the rear brake line
-> after the stock cutoff block (should no longer perform the

I've seen some people mount the valve conveniently on the trans tunnel.
Unfortunately, that places it in a high spot that makes it very hard to
bleed short of standing the car on its nose, parking downhill in San
Francisco, or loosening the fitting and drooling brake fluid in the
passenger compartment.

You need to make sure you don't create an air pocket in the system, or
you'll get mushy brakes.