Proportional valve for Chevy disc conversion

[Gas Pig]

If I’m planning on running the Chevy disc conversion on my D44 but still keeping stock 9” drums in the rear can I use the proportional valve from ‘76-77 Bronco?

Thanks Jeff

 

[Rustytruck]

chevy disc conversion on my 1974 didn't need the proportion valve even with hydra boost conversion. still running the stock H block. If you must use a proportion valve consider mounting it up by the master cylinder out of the engine heat zone. modern proportion valves are prone to leaking in a very short period of time when mounted down by the exhaust manifolds.

 

[pcf_mark]

The Camaro master cylinder has two different sized ports to act as the proportioning valve. You do not need a separate one unless you have something really adventurous going on.

 

[Gas Pig]

Actually I’m not sure if I want to go with the hydro boosters or vacuum booster. So I’m open to suggestions.

For some reason I don’t remember reading about the Camaro masters cylinder and I always though the H block really was the setup for drum front and rear which really was a proportion valve. It’s there just in case you blow one line or the other and the switch trips and you still have some sort of brakes.

So maybe I’m not understanding everything correctly?

 

[DirtDonk]

The H=block is not a proportioning valve of any sort. It's just a simple distribution block with the shuttle and dash warning light switch. There's still some debate as to whether or not the tripping of the shuttle to one side or the other has any reduction effect. I used to think it shut off the flow to the effected lines, but don't think it does.

The primary reason that a prop valve was not used as far as I know is that instead of a control valve, the designers sized the brakes according to their position and expected use. So the rears are simply less powerful than the fronts, based on overall size of the friction surfaces and the size of the wheel/slave cylinders.
Once they started doing disc front options on different vehicles with different needs (think empty pickup beds, vs full pickup beds) and different types of valves had been developed for improved safety, we got the one commonly seen as a proportioning valve (but actually called a "combination valve") that you see most of the time from the factory, including on Broncos with disc brakes.

And yes you can use one. It might be the best one, but it's not the most versatile unfortunately. I'm a big fan of them, but have been recommending against their use for many years. Mostly because the aftermarket versions leak so often and that SUCKS!
I sure hope someone will, or already has come out with a higher quality version, but until I hear about it or see it in person, I'll still recommend the manually adjustable one (including these: https://www.wildhorses4x4.com/category/s?keyword=proportioning+valve) for any brake swaps and most modified Broncos.

That's because you're mis-matching brakes compared to what came from the factory, and if you've modified your Bronco including lift height, tire size, added weight of accessories, etc you could benefit from being able to fine-tune your rear brakes according to your own personal needs.

The real combination valves like you are talking about has a pre-set amount of reduction to the rear brakes (the proportioning part) that might or might not be well suited to your particular Bronco. That's where the adjustable type come in handy.
Is your Bronco mostly stock that you're putting this on? If so, then a standard combination valve might work perfectly. If you can find a stock one in good shape those do not generally leak, so you'd be good there. It's just the aftermarket ones that look like a machined brass or aluminum block that leak out of the metering valve.

The other features of the stock type are still very desirable however. The "delay valve" (also called "metering valve" and "hold-off valve") delay the application of the front brakes to allow the rear drums to catch up so to speak. This reduces nose-dive on hard stops and also helps to stabilize the vehicle during braking.
Keeping the dash mounted warning lamp is a nice safety feature too.
The proportioning of pressure to the rear under hard braking is obviously a good thing, but if it's not correct for your setup, or leaks out of the delay valve, then it was not worth the trouble.

I notice that Wilwood has one of the standard combination valves now (maybe they've had it all along and I just never noticed?), and I would hope that theirs are of better quality than the ones from some other companies, but I don't know until people try them. So I still like the adjustable one.
There are combinations you can put together yourself, as most of the separate functions of the combo valve are available to buy separately. It would just be nice if they were all in one single body like the factory stuff.

As was mentioned though, no matter which you try, even the factory style can benefit from being mounted up by the master. Especially if you run exhaust headers.

Paul

 

[DirtDonk]

The Camaro master cylinder has two different sized ports to act as the proportioning valve. You do not need a separate one unless you have something really adventurous going on.

Never heard of that before. I've seen aftermarket masters with all the components built into them, but was not aware of a factory setup. Got a link to the part, or at least a specific model and year that they were available on?

It might be built in, but I would not think that the different size port is actually a prop valve. Must be something more built into it. Even Broncos had different size ports on the master. Well, the port was the same size but the threaded fittings were different so you didn't mess up front and back.
Pretty much every factory master cylinder I've ever seen had different size port fittings.

got more info on it?

paul

 

[DirtDonk]

The aftermarket masters with the built-in prop valves that are still adjustable seem like a pretty cool idea.
Prop valve in the rear circuit, delay valve in the front circuit, built-in brake light switch (but not the warning light I don't think) and all you'd need to put icing on the cake would be a pair of residual pressure check valves to complete your system in a fairly compact assembly.

Anybody tried anything like that yet? Whether on your Bronco, or any other car, truck or hot-rod you might happen to have built?

Paul

 

[pcf_mark]

Never heard of that before. I've seen aftermarket masters with all the components built into them, but was not aware of a factory setup. Got a link to the part, or at least a specific model and year that they were available on?

It might be built in, but I would not think that the different size port is actually a prop valve. Must be something more built into it. Even Broncos had different size ports on the master. Well, the port was the same size but the threaded fittings were different so you didn't mess up front and back.
Pretty much every factory master cylinder I've ever seen had different size port fittings.

got more info on it?

paul

As I understand it (I do not have a direct engineering info) the bore of the master cylinder is a fixed size (obviously) but by staggering the size of the outlets to the front and rear they change the pressure going to that leg of the system. If I have 100 psi pushing on a 1/4" area it will have different force exerted than if the 100 psi is pushing on a 3/8" area. Same 100 psi but the force exerted on the other end (pistons or wheel cylinders) should change. Or it could be the volume displaced is reduced to one leg making that leg of the system require more or less force (volume) to get a change.

 

[Gas Pig]

The H=block is not a proportioning valve of any sort. It's just a simple distribution block with the shuttle and dash warning light switch. There's still some debate as to whether or not the tripping of the shuttle to one side or the other has any reduction effect. I used to think it shut off the flow to the effected lines, but don't think it does.

The primary reason that a prop valve was not used as far as I know is that instead of a control valve, the designers sized the brakes according to their position and expected use. So the rears are simply less powerful than the fronts, based on overall size of the friction surfaces and the size of the wheel/slave cylinders.
Once they started doing disc front options on different vehicles with different needs (think empty pickup beds, vs full pickup beds) and different types of valves had been developed for improved safety, we got the one commonly seen as a proportioning valve (but actually called a "combination valve") that you see most of the time from the factory, including on Broncos with disc brakes.

And yes you can use one. It might be the best one, but it's not the most versatile unfortunately. I'm a big fan of them, but have been recommending against their use for many years. Mostly because the aftermarket versions leak so often and that SUCKS!
I sure hope someone will, or already has come out with a higher quality version, but until I hear about it or see it in person, I'll still recommend the manually adjustable one (including these: https://www.wildhorses4x4.com/category/s?keyword=proportioning+valve) for any brake swaps and most modified Broncos.

That's because you're mis-matching brakes compared to what came from the factory, and if you've modified your Bronco including lift height, tire size, added weight of accessories, etc you could benefit from being able to fine-tune your rear brakes according to your own personal needs.

The real combination valves like you are talking about has a pre-set amount of reduction to the rear brakes (the proportioning part) that might or might not be well suited to your particular Bronco. That's where the adjustable type come in handy.
Is your Bronco mostly stock that you're putting this on? If so, then a standard combination valve might work perfectly. If you can find a stock one in good shape those do not generally leak, so you'd be good there. It's just the aftermarket ones that look like a machined brass or aluminum block that leak out of the metering valve.

The other features of the stock type are still very desirable however. The "delay valve" (also called "metering valve" and "hold-off valve") delay the application of the front brakes to allow the rear drums to catch up so to speak. This reduces nose-dive on hard stops and also helps to stabilize the vehicle during braking.
Keeping the dash mounted warning lamp is a nice safety feature too.
The proportioning of pressure to the rear under hard braking is obviously a good thing, but if it's not correct for your setup, or leaks out of the delay valve, then it was not worth the trouble.

I notice that Wilwood has one of the standard combination valves now (maybe they've had it all along and I just never noticed?), and I would hope that theirs are of better quality than the ones from some other companies, but I don't know until people try them. So I still like the adjustable one.
There are combinations you can put together yourself, as most of the separate functions of the combo valve are available to buy separately. It would just be nice if they were all in one single body like the factory stuff.

As was mentioned though, no matter which you try, even the factory style can benefit from being mounted up by the master. Especially if you run exhaust headers.

Paul

Hey Paul, as always you have lots of great info! As for my truck I’m planning on mating 302(maybe a Holly snipper) to AOD with 4.11’s and running 31” sitting on 2.5” lift. The question is vacuum or hydro booster???

Way back in 2004 I built a ‘72 with a ‘89 Mustang motor with Mark IV hydro booster with Chevy disc and drum rears. I ran the front through the H block (only because it was there) and the back through an adjustable single Wilwood valve. The brakes seemed great at the time. But it’s many years later and there are more options to choose from. Honestly if you had my setup what would you run vacuum or hydro and you named a few proportional value setups... what should I try first?

Thanks again for you time and help! Honestly that goes for all the guys who jumped in on the conversation!

 

[DirtDonk]

...running 31” sitting on 2.5” lift. The question is vacuum or hydro booster???

Honestly if you had my setup what would you run vacuum or hydro and you named a few proportional value setups... what should I try first?

I'd go with door number three. Manual brakes first.
I know that's counter-intuitive for those used to power brakes on everything, but 31" tires are not beyond the capabilities of regular old brakes.
However, on the street and for someone that likes extra easy brake pedal push, a vacuum booster is plenty even though most of the current crop of them are weaker than the originals. Or at least seem to be from my limited experience.
But the good thing about manual is that, first you don't have to do the extra plumbing and through the extra expense. Second it gives you a real direct comparison experience when you do add the booster.

I think it's pretty well documented that hydro-boost is "better' or at least more powerful than a standard Bronco-sized vacuum booster. Also takes up at least slightly less space. At a greater initial cost if you buy the parts new.
But as a general rule-of-thumb around here, a vacuum booster is more than a match for a 31" tire.
I like the less plumbing aspect of vacuum, but with larger tires the power of the hydro-boost is hard to ignore.

Which is a long way of saying, "it's up really to you bud";D

Paul

 

[sprdv1]

I'd go with door number three. Manual brakes first.
I know that's counter-intuitive for those used to power brakes on everything, but 31" tires are not beyond the capabilities of regular old brakes.
However, on the street and for someone that likes extra easy brake pedal push, a vacuum booster is plenty even though most of the current crop of them are weaker than the originals. Or at least seem to be from my limited experience.
But the good thing about manual is that, first you don't have to do the extra plumbing and through the extra expense. Second it gives you a real direct comparison experience when you do add the booster.

I think it's pretty well documented that hydro-boost is "better' or at least more powerful than a standard Bronco-sized vacuum booster. Also takes up at least slightly less space. At a greater initial cost if you buy the parts new.
But as a general rule-of-thumb around here, a vacuum booster is more than a match for a 31" tire.
I like the less plumbing aspect of vacuum, but with larger tires the power of the hydro-boost is hard to ignore.

Which is a long way of saying, "it's up really to you bud";D

yes sir...…..