since i don't want to change much, i think i will try to find a restoration source or ebay to replace with an original. thanks for the feedback.

by the way, what is it's main function along with the smaller unit right above it?

 

Proportioning valves decraeses the pressure to the rear brakes so they won't lock up prematurely, especially when all your inertia shifts forward in a hard stop. Adjustable ones let you play with this pressure to find the right setting. The thing above it? Were you asking me, earlymustang?

[IMG]local://upfiles/3913/D89FEF4CBF844B62B825B052FE901A91.jpg[/IMG]

 

A proportioning valve is used in the rear to decrease the rate of pressure rise to the drums relative to the pedal force as weight is shifted to the front during braking. This prevents the rear from locking up under hard braking conditions.

 

Remember one thing, Proportioning valves have their purpose and they are not always needed. Each car differs and due to the front to rear weight distribution and how your brakes are performing under those conditions will determine if you need it or not. That's why I set my system up first without it and ran a test under hard braking. Mine did not lock up the rears so, she goes without it. Now, when I did this conversion on my 69 Road Runner, the rears locked up so, I then installed the Proportioning valve. It's more work to do it this way but, I don't believe in using a Proportioning valve if I don't need it.

 

find a patch of safe tar and start out at 30 mph apply brakes quickly until something locks. If the front lock up first then you dont need the valve. If the rear lock up then you can increase your braking performance by adding the valve.

My mustang did need the valve and I did notice a decrease in stoping distace after it was adjusted correctly

GUn

 

Here are some good Q and A about valves taken from the Master power brake site

What does a proportioning valve do? A proportioning valve is used in the rear to decrease the rate of pressure rise to the drums relative to the pedal force as weight is shifted to the front during braking. This prevents the rear from locking up under hard braking conditions.

What are the symptoms of a bad proportioning valve? If your prop valve has gone bad your rear wheels will lock up easily, especially on wet surfaces.

What does a metering valve do? A metering valve or "hold off valve" is used in the disc portion of a disc/drum system to hold off the application of the front discs slightly allowing the slower reacting rears to catch up. This provides rear stability on wet surfaces and reduces excessive pad wear.
What are the symptoms of a bad metering valve? Your car will nose dive and the front pads will wear too fast.

What does a residual valve do? There are two different uses for residual valves. The 10 lb valve is used to hold a residual pressure to the drum brakes to give a higher firmer pedal. The 2 lb valve is used in the disc when the master cylinder is lower than the calipers to prevent back siphoning of the fluid from the master.

What are the symptoms of a bad residual valve? The brakes will be very spongy and you will need to pump the pedal to get good brakes.

What is a combination valve? A combination valve incorporates metering and proportioning into one valve providing all necessary valving for disc/drum systems.


Should I use an adjustable proportioning valve? Not if you can help it. The adjustable valve will only provide the proportioning function and not the metering that is needed.

 

A couple of places I just found in case anybody needs one in the future.

White Post Restorations
540-837-1140

and/or 65-66 T-Bird

Good news and bad news: The good news is that the brake distribution blocks are available and I finally found the source of the leak coming from the driver side frame rail (fluid running from the valve down under). The bad news is the dist. blocks are 50 bucks and a new or restored prop valve is not cheap. And... brake fluid makes a mess when mixed with paint and undercoating. The master cylinder was restored last year so that's at least one less thing.

Oh, when I re-install the new prop. valve, block and the lines, I'm assuming I will need to bleed the whole system?

 

Yep, anytime you break a connection in the brake system, you better bleed the whole system.

And yes, regular brake fluid will eat up paint in nothing flat. That is why I opted for the more expensive silicone fluid - if you spill it, it doesn't eat the paint. Since I started with an entirely new system, I could use either reglar Dot 3/4 or silicone. I believe if you want to use silicone in a system that was previously regular fluid, you have to flush/bleed out the entire system.