Drum/drum to disk/disk proportioning valve

[rumblin46]

What has everyone done when doing a 4 wheel drum to 4 wheel disk set up? I am still using the factory 69 differential valve and all brakes work however I wonder if there's a better "way". I see JBG has a disk/disk prop valve for a reasonable price.

Thanks!

[Madman]

I'm doing an all wheel disc conversion, and intend to get the same valve you are speaking of from JBG, if that helps!

[HIO Silver]

Wilwood... $78.

[Fuzzyhead]

I'm looking for a new proportioning valve as well. Does the Willwood word on drums for a '71 F-100?

[HIO Silver]

I'm looking for a new proportioning valve as well. Does the Willwood word on drums for a '71 F-100?

Yes. It's adjustable.

[rumblin46]

Thanks for the responses!

[rumblin46]

Any particular master cylinder? Or has the stockers worked?

[rumblin46]

Just to update, installed the WIlwood proportioning valve($68, Amazon). Definitely a worth while investment. I did find the old dist. valve was blocking the rear brakes...took an overnight soak in order to get the valve free.

[HIO Silver]

Any particular master cylinder? Or has the stockers worked?

A disc/drum MC will work.. the rear line will just be metered by the prop valve.

Just to update, installed the WIlwood proportioning valve($68, Amazon). Definitely a worth while investment. I did find the old dist. valve was blocking the rear brakes...took an overnight soak in order to get the valve free.

... and that's precisely why I ditched the factory dist/prop valve. Ford doesn't even sell a rebuild kit/service pack for it. That's where the aftermarket comes through with waaaay better components.

[ultraranger]

DOT 3, 4 and 5.1 brake fluids are glycol-based fluids. 5.1 meets the standards of DOT 5 silicone fluids, for dry and wet boiling points but, 5.1 is not silicone fluid and it's not compatible with DOT 5 (silicone) brake fluid.

DOT 3, 4 and 5.1 brake fluids are hygroscopic. That's just a fancy word that means the brake fluid absorbs moisture from the air. Even though a brake system is a sealed/closed system, it can easily absorb 2% moisture into the fluid a year. The most common points for air to enter the brake system comes from the vent, and air space above the seal, in the MC cover (on a conventional, old style, MC --with a cast iron or cast aluminum body with the large cover). A large amount of moisture from the air will be introduced into the fluid whenever you remove the MC cover and most especially if you leave the cover open for an extended period.

Air will also permeate the rubber hoses connecting the hard lines to the brakes. The brake fluid molecules are too large to pass through the pores of the hoses but, the air molecules are small enough to get through the hoses and the moisture and debris will slowly accumulate in the fluid and settle in the components over time.

Moisture accumulation in the brake system will cause rust flakes on the inner portions of anything that is ferrous. This will erode brake components and the debris will clog/gum up passages and components. The passages of the pressure differential valve or combination valves are fairly small. Contamination will gum up these valves and make them stick, which can make it very difficult to recenter the pressure differential spool (the component inside the brake valves that triggers the brake warning light on the dash).

Glycol-based brake fluids should be flushed out and replaced no longer than every 24 months, whether the vehicle is being used frequently, infrequently or not at all. Keeping the brake fluid changed will alleviate a lot of brake and brake component malfunctions.

[rumblin46]

DOT 3, 4 and 5.1 brake fluids are glycol-based fluids. ....

Good info!

[marvin2]

Ok...this is an area that I have had some question as well. I will ultimately have a disc / disc setup as well. If I understand this correctly, as long as I am going with an adjustable proportioning valve, it does not make a difference whether I run a drum / drum or a disc / drum master cylinder?

Thanks guys....

[rumblin46]

It appears to not matter, seems like manual/power brake booster is more of a potential issue.

[ultraranger]

Ok...this is an area that I have had some question as well. I will ultimately have a disc / disc setup as well. If I understand this correctly, as long as I am going with an adjustable proportioning valve, it does not make a difference whether I run a drum / drum or a disc / drum master cylinder?

Thanks guys....

It's really better to use a MC that's actually designed for the type of brakes you'll be running.

If a drum/drum MC was fine to run with a disc/drum or a disc/disc brake system, auto manufacturers wouldn't have invested the engineering time and cost of materials to come up with the different MCs. Each are designed for the specific brake types that they will operate. Other MCs for a different brake setup than what you have may "work," or operate the brakes but, the brakes won't be "working" like they should.

If the bore diameter is the same for both the primary and secondary sides of the MC, then the pressure coming out of the primary and secondary ports of the MC will be equal. --the '87-'93 5.0L Mustangs are the only Ford (disc/drum) MCs I can think of that don't have equal bore sizes (1-3/16" primary bore and a 13/16" secondary bore).

The purpose of a proportioning valve is to reduce the rate of pressure rise to the rear brakes, in a panic stop situation, to help reduce the chances of the rear brakes locking up in an effort to keep the rear end of the vehicle from swapping ends with the front.

Up to the point of proportioning, the brake pressure output of both MC ports will be equal. Once the brake pressure spikes to a given point (known as the knee point), the rate of pressure rise to the rear brakes is reduced in relation to the fronts.

Factory proportioning valves are contained within the valve body assembly of the combination valve for disc/drum or disc/disc vehicles but, proportioning valves are not installed in a factory pressure differential valve for a drum/drum equipped vehicle.

Factory proportioning valves have a spring of a given wire thickness that's designed to regulate the pressure at a predetermined pressure level that's calibrated to the particular vehicle. An aftermarket add-on manually-adjustable proportioning valve is typically designed to operate from zero restriction to a maximum of 57% pressure reduction. This means with the knob set at full restriction, it's still 43% open.

Unless you know what the percent of pressure reduction should be for your particular application and adjust the manual proportioning valve to that specific pressure setting, with a set of brake gauges, any setting adjustment outside of that (through a series of hard stops in trying to see at what point the brakes lock up and when) is just going to be a guess. In the mean time, it may mean that you'll grind a lot of rubber off your tires trying to set the valve at what you think is the right setting. --if you're trying to set a manual proportioning valve with the lock-the-tires-up method, don't do it on dirt or gravel. It will have to be done on asphalt to be anywhere close to right.

[HIO Silver]

Ok...this is an area that I have had some question as well. I will ultimately have a disc / disc setup as well. If I understand this correctly, as long as I am going with an adjustable proportioning valve, it does not make a difference whether I run a drum / drum or a disc / drum master cylinder?

Thanks guys....

You understand incorrectly..... because of the reservoir capacity. It takes more fluid to move front disc pistons which have lots of surface area than a lil drum slave cylinders.

If swapping to front discs, opt for a disc/drum MC with an adjustable PV to the rear. The it is only a matter of swapping to rear discs and adjusting the front/rear bias. Rear disc calipers use smaller pistons so the reservoir for the rear drums is A-OK.

Below is a visual of disc pistons. Compare them to drum slave cylinders...: