Split Brakes

[Stan Leschert]

I think that this is an idea worth looking into. This very problem, may keep the current fleet of Canadian MLVWs (deuce) from being released for sale except as salvage parts. If it can happen up here, it WILL hapen in the USA....You have way more lawyers than we do!
It seems to be up to us to correct the Military's mistakes and finally build something right! We are the only ones who can save our hobby! Let's get the smarter members to find a fix. Could even be some money to be made here!

 

[stumps]

If you're going to custom mod a dual master cylinder setup, why stop there? Heck, make it a 3 master cylinder setup. Run extra hard lines to the rear-rear if needed. That way you don't have to worry about proportioning valves at all. And you would have triple redundant brakes.

Just install a pivot system on the brake pedal to negate the "hair trigger" effect from pumping 3x the fluid for the same pedal push.

Or you could run your two master cylinder kit into left & right instead of front/back. Sure it's goofy. But in an emergency it would work. Well, it would work if you have tons of upper body strength to keep the thing on the road. That also would not require any proportioning.

I kind of like the triple master cylinder idea though.

I have no idea how all the air assist stuff works. I'm planning to read up on it real soon. But surely you could tee off the air lines & put a larger air tank on?

What you propose won't work unless you are a gorilla!

Some simple hydraulics needs to be discussed:

First, PSI, or pounds per square inch, tells a large part of the story of how hydraulics works. Hydraulic systems are effectively a variation on the lever.

Some examples contrived to have simple numbers:

1) A system with one master cylinder (MC), and one wheel cylinder (WC):
If the MC piston is 1 square inch area, and the WC piston is 2 square inchs area, 20 lbs of force from the WC piston will require 10 lbs of force on the MC piston. The MC's piston will have to move twice as far as the WC's piston.

2) A system with one master cylinder (MC), and two wheel cylinders (WC):
If the MC piston is 1 square inch area, and the WC pistons are 2 square inches area each, 20 lbs of force from each WC piston will require 10 lbs of force on the MC's piston, but the MC's piston will have to move 2 times the distance each WC piston has to move, or twice as far as the MC in example #1. [This is a 1 axle system.]

3) A system with one master cylinder (MC) and four wheel cylinders (WC):
If the MC piston is 1 square inch area, and the WC pistons are each 2 square inches area, 20 lbs of force from each of the four WC pistons will require 10 lbs of force on the MC's piston, but the MC's piston will have to move 2 times the distance each WC piston has to move, or four times as far as the MC in example #1. [This is a 2 axle system, like a normal car. A 3 axle system works the same, but multiplies by 3.]

And finally, the two master cylinder example:
4) A split system with two separate systems each the same as in example #2, will need twice the force to move both MC pistons as in example #2, but the MC piston will move half as far as the MC piston in example #3.

And a three master cylinder example:
5) A split system with three separate systems, each the same as in example #2, will need three times the force to move the three MC pistons as in example #2.

Please note that each wheel cylinder will need to provide the same amount of force, to the brake shoes, to stop the deuce regardless of the MC configuration.

If you use two normal deuce master cylinders in your redundant system, you will double the force at the brake pedal needed to stop the deuce. If you use 3 normal deuce master cylinders in your redundant system, you will triple the force at the brake pedal needed to stop the deuce...

Basically, your redundancy will make it physically impossible for you to apply enough pedal force to stop your deuce if the air assist quits. Even if the air assist is working, your redundancy will multiply the brake pedal force by the number of redundant MC's.

The only way to make a split circuit system work would be to use a MC that has two pistons, each with 1/2 the area of the original, but traveling twice as far.

-Chuck

 

[m-35tom]

keep in mind also that the m/c does NOT apply the brakes. it only controls the air regulator on the air pack. also talk of a proportioning valve simply does not apply when you have all drum brakes. so it comes down to this: you need 2 air packs and a way to control the air to them.

 

[Unforgiven]

Chuck that's true,

But 3x the force wouldn't be that difficult to accomplish with a modified pedal. It's just a lever after all.

"Give me a long enough lever and a fulcrum on which to place it and I shall move the world"
~ Archimedes

A modified pedal could be made to have the exact same force as it is now with a single MC. The MC piston would only have to travel 1/3 the normal distance b/c it's not feeding 12 wheel cylinders, only 4. So in theory, simply moving the connection point of the MC plunger 2/3 closer to the pivot would give you 3x the force on the MC plunger with the same pedal push depth & force as the original. The trade off is the MC plunger would only push 1/3 as far as it used to. But that's ok because that's all it needs to push to force 1/3 the number of wheel cylinders to fully expand.

Like I said, it's goofy. But it would probably work.

I read a post here where some guy used a power steering assist from some International truck. Honestly, that sounds like the best solution & gives an excuse for wanting power steering.

 

[stumps]

keep in mind also that the m/c does NOT apply the brakes. it only controls the air regulator on the air pack. also talk of a proportioning valve simply does not apply when you have all drum brakes. so it comes down to this: you need 2 air packs and a way to control the air to them.

Not quite true. When you press the pedal, there is a small amount of wasted motion that is used to open the valve on the air assist regulator, and that drives the master cylinder.... However, if anything in the air system fails, once the pedal passes through that wasted motion, you are directly driving the master cylinder plunger. In an air pack failure situation, two master cylinders will require twice the pedal force, all things being equal.

-Chuck

 

[stumps]

Chuck that's true,

But 3x the force wouldn't be that difficult to accomplish with a modified pedal. It's just a lever after all.

"Give me a long enough lever and a fulcrum on which to place it and I shall move the world"
~ Archimedes

A modified pedal could be made to have the exact same force as it is now with a single MC. The MC piston would only have to travel 1/3 the normal distance b/c it's not feeding 12 wheel cylinders, only 4. So in theory, simply moving the connection point of the MC plunger 2/3 closer to the pivot would give you 3x the force on the MC plunger with the same pedal push depth & force as the original. The trade off is the MC plunger would only push 1/3 as far as it used to. But that's ok because that's all it needs to push to force 1/3 the number of wheel cylinders to fully expand.

Of course, but now you are redesigning even more of the braking system. The additional hole in your brake pedal lever arm could weaken the brake pedal and add another single point failure to the system.

The simplest solution would be to go to your local light truck parts dealer, with a deuce master cylinder, and buy the dual chamber version of the current master cylinder. That option was available for the vacuum assist master/slave system in an old Ford 600 I had. The dual chamber master cylinder will have pistons that are 1/2 the area of the original, and travel twice as far.

-Chuck

 

[Unforgiven]

Of course, but now you are redesigning even more of the braking system. The additional hole in your brake pedal lever arm could weaken the brake pedal and add another single point failure to the system.

The simplest solution would be to go to your local light truck parts dealer, with a deuce master cylinder, and buy the dual chamber version of the current master cylinder. That option was available for the vacuum assist master/slave system in an old Ford 600 I had. The dual chamber master cylinder will have pistons that are 1/2 the area of the original, and travel twice as far.

-Chuck

But Chuck, with twice the plunger travel on the MC you will still have to modify the pedal. Otherwise when the pedal is pushed flat to the floor, the MC plunger is only 1/2 pushed, and creates only 1/4 of the volume of fluid displaced as before. That doesn't sound safe to me. The force on your 1/2 diameter MC plunger would be reduced by a factor of 4 on your feet. So you would have really soft brakes that hit the floor without engaging the wheel cylinders.

You cannot escape the fact that Work/Energy = Force x Distance

If you use a smaller diameter plunger the force will be less and therefore your pedal must travel further.

Force x Distance at the wheel cylinders must equal Force x Distance at the Master Cylinder. In all cases, it's the pedal arc that is constraining the system. The only way to get "softer" brakes and keep full wheel cylinder engagement equal to original is to modify the pedal.

I would assume anyone tackling something like this knows how to weld & reinforce a piece of brake pedal. The strength of mild steel is 30,000 psi. The pressure the brakes can withstand without blowing a cylinder somewhere is 1800 psi. We're talking an entire order of magnitude difference. Even with 3 MC's making 3x the back force on the pedal/plunger connection it won't even come close to shearing even mild steel.

I'm telling you, that power steering guy who ripped out the air system is probably the best way if you can afford it.

But, the reason I dusted off this link is because I wanted the 2 MC guy to realize that 3 MC would be just as easy to engineer & provide even more "safety backup" in an emergency.

Also, my above argument applies only to hydraulics, not the air assist. I'm planning to read up on that today or tomorrow.

 

[rflegal]

If you're going to custom mod a dual master cylinder setup, why stop there? Heck, make it a 3 master cylinder setup. Run extra hard lines to the rear-rear if needed. That way you don't have to worry about proportioning valves at all. And you would have triple redundant brakes.

Just install a pivot system on the brake pedal to negate the "hair trigger" effect from pumping 3x the fluid for the same pedal push.

Or you could run your two master cylinder kit into left & right instead of front/back. Sure it's goofy. But in an emergency it would work. Well, it would work if you have tons of upper body strength to keep the thing on the road. That also would not require any proportioning.

I kind of like the triple master cylinder idea though.

I have no idea how all the air assist stuff works. I'm planning to read up on it real soon. But surely you could tee off the air lines & put a larger air tank on?

The 3 master cylinder option is cool, but would again require an additional air pack and an additional air tank to truely isolate the system. The goal is to have at least one axle with brakes given a failure in the system. The only common point of connection is the brake pedal and the air compressor in the dual MC setup. You could do three, but thats another MC, air pack, tank, and lines. Somewat overkill. I would do the diagonal first. I believe that's standard on some vehicles.

 

[stumps]

But Chuck, with twice the plunger travel on the MC you will still have to modify the pedal. Otherwise when the pedal is pushed flat to the floor, the MC plunger is only 1/2 pushed, and creates only 1/4 of the volume of fluid displaced as before. That doesn't sound safe to me. The force on your 1/2 diameter MC plunger would be reduced by a factor of 4 on your feet. So you would have really soft brakes that hit the floor without engaging the wheel cylinders.

Read what I said again. I said 1/2 area, not 1/2 diameter!

-Chuck

 

[Unforgiven]

Read what I said again. I said 1/2 area, not 1/2 diameter!

-Chuck

Ok, half the area. With the same pedal displacement, that is pushing the brake pedal all the way until it bottoms out on the floor, you are still only moving 1/2 the volume of brake fluid compared to bottoming out the original master cylinder.

Unless you plan to keep the brake shoes new & adjusted tight at all times, it's not going to work.

V=A*L where L is the push of the MC plunger.

So now you are talking about Vnew = 1/2A*L because L is fixed by the bottoming out of the brake pedal. Therefore, Vnew is 1/2 of the original volume. You're idea would work if the brake pedal was allowed to travel twice as far. Is that possible to maintain as the brake shoes wear? I don't know. It seems to me the new system should be engineered to push at least the same amount of fluid as the original system. What you propose can only push 1/2 that amount maximum. Is that enough? Hey, it's your truck.

Personally, for the money, the power steering guy is right. You could add Ram assisted steering (note, assisted is not the same as direct Ram steering & is perfectly DOT legal) & at the same time do the hydraulic assisted brakes. You could even keep the air assist hooked up in an emergency situation where the engine dies & you lose hydraulics. Now that's a truly redundant system. It would have regular brake hydraulics, assisted power steering hydraulics, and air assist as a last resort. You could use 24V pneumatic solenoids to flip the air on in an emergency.

Your idea is good in theory. But unless you are planning to raise the pedal hight into you knees while driving it's not going to work in practice.

 

[Snarky]

You could just find a master cylinder for a topkick or a ford f-700 or a school bus, generally these systems are hydroboost or electric over hydraulic and can be fitted to most any vehicle with modifications, it's not difficult people, it's just expensive. These systems are overkill compared to the deuce's brake system, but you can adjust the brakes to compensate.

I was going to fit a chevy hydroboost and master to my truck mounted in the stock location with a custom bracket, with a small power steering pump with a v-belt pully, but my brakes are going just fine for now, I have most of the parts, one day I'll get industrious.

 

[stumps]

Ok, half the area. With the same pedal displacement, that is pushing the brake pedal all the way until it bottoms out on the floor, you are still only moving 1/2 the volume of brake fluid compared to bottoming out the original master cylinder.

Unless you plan to keep the brake shoes new & adjusted tight at all times, it's not going to work.

I'm not planning on doing anything to the single circuit brakes on my deuce. I have used single circuit brakes on many different vehicles, for close to a million miles, without failure. So I don't really see them as that much of a safety problem. Maintain them even slightly, and they won't fail. I have had dual circuit brakes that have failed completely. Twice with master cylinder failures (which were completely hidden from routine inspection), and once with a rusted brake line (which I would have replaced during routine maintenance had I not had dual circuit brakes).

Fortunately I drive so conservatively that I hardly need service brakes at all. In each of the brake failures I have had, I was able to control the vehicle by a combination of down shifting, steering, and the parking brake.... and as always a little luck.

(Statistically, there is a 1 in 350 chance that you will be involved in a fatal car crash in your time as a driver. Luck is most important in life!)

You pay your money and take your choice: If you go to two pistons with the same area as the original deuce piston, or two deuce master cylinders, you are going to increase the force on the master cylinder's rod(s) to double what it currently is. You can either change the bell crank's ratio, or reduce the area of the master cylinder's piston. Reducing the area of the master cylinder's piston is going to increase the sensitivity of the pedal to brake shoe wear. Changing the bell crank's ratio won't. So I agree, changing the bell crank is probably a more correct answer.

However, the bell crank isn't safe to modify. It is a forging, and it isn't going to lend itself to simply moving the connection point that drives the master cylinder. Cutting the bell crank shorter, to increase its leverage, and re-welding it is just going to introduce another single point failure mode, and will require repositioning the mount for the master cylinder.

I'd recommend leaving the system as it is, and maintaining it carefully... And so I shall.

-Chuck

 

[Unforgiven]

What's the approximate stopping distance on dry highway from say 50 mph assuming the brakes are in good working order? I'm just curious.

 

[stumps]

A couple of things to remember when working with hydraulic piston systems: First is that hydraulics are a form of leverage. Anything you can do with a lever, you can do with hydraulics.

And second, if you use two equal sized master cylinders, or a dual chamber master cylinder with equal sized cylinders it is absolutely essential that each circuit drive the same number, and size, of wheel cylinders.

It won't do to have one master cylinder drive the two rear axles, and the other drive the front axle. If you do that, the front wheel cylinder's pistons will move at twice the rate of the rear. That will result in the front wheels locking up when the rear wheels are half way to locking up... if you get my meaning.

-Chuck

 

[Unforgiven]

A couple of things to remember when working with hydraulic piston systems: First is that hydraulics are a form of leverage. Anything you can do with a lever, you can do with hydraulics.

And second, if you use two equal sized master cylinders, or a dual chamber master cylinder with equal sized cylinders it is absolutely essential that each circuit drive the same number, and size, of wheel cylinders.

It won't do to have one master cylinder drive the two rear axles, and the other drive the front axle. If you do that, the front wheel cylinder's pistons will move at twice the rate of the rear. That will result in the front wheels locking up when the rear wheels are half way to locking up... if you get my meaning.

-Chuck

Probably best to just leave the system alone, flush it thoroughly, & replace all the wheel cylinders, shoes, and MC. The pinion parking brake might be useful as a backup emergency brake as well, even though it's not designed for that. But if the system ever did fail it would be nice to have both the driveline e-brake and the pinion brake.

Why can't you just buy an A3 master cylinder and all new A3 wheel cylinders. Wouldn't that work?

 

[WyoDeuce]

I was reading about the 10 ton 6x6 last night. They are equiped with a cutting brake to help steer off road with heavy loads. The 10 ton pulls so hard that the front tires can have trouble steering because very little weight is on them. I didn't find any info if they were single or dual circuit. I think if you were converting to dual circuit this would be a neat option for off road driving.

 

[pjpiche1]

I am going to keep my single circuit system. My duel circuit system on my Dodge 2500 truck failed on the front. The drivers side rubber hose burst. I had complete brake failure. Complete brake failure is complete brake failure no matter how you put it!

 

[DanMartin]

The pinion parking brake might be useful as a backup emergency brake as well

The parking brake is just that...a parking brake. Using it to try and stop a moving vehicle only makes a lot of smoke. Try it sometime....it's useless to stop from any speed. Downshifting is really your only hope.

Why can't you just buy an A3 master cylinder and all new A3 wheel cylinders. Wouldn't that work?

See my post earlier in this thread about all of the new parts needed to make the system work. While not impossible, it is a lot of work. If you've ever been under a split-brake system truck and looked at the plumbing required, you'd think twice about it too.

I think the lesson here is...maintain your truck well, inspect it every time you take it out, and don't cut corners and the brakes will be fine. Don't do these things and you could kill yourself or someone else and give our hobby a bad name. Upgrading to a split brake system (while a great discussion topic) is probably not feasable for most people...so just make sure that your single-circuit system is in tip top condition at all times, and every time. A few hundred dollars investment in flex hoses, fluid, seals, and a master cylinder will go a long way to ensuring that the truck is safe. Don't trust parts that may be up to 50 years old!.

The braking system on these trucks, while not without fault, is actually not bad if you think about the time they were designed in. Assuming the system is in good working order it will stop even a loaded truck in a reasonable distance. The split system does nothing to improve this.

 

[clinto]

I have read this thread with great interest, as I would like to have the additional safety of a dual circuit system, but as no one has brought this up yet, I guess I will.

A lot of different ideas have been proposed in the last 8 pages....... but why do you think the manufacturer (AM General) or the military (they do have a hand in this sort of thing-they could simply tell the people bidding on a contract "we want it THIS way") went the way they did?

All the proposals here were at their disposal as well....... so why do you think they went the way they did? If they could have done it this easily with off the shelf parts, they could lower the price of the bid and have better chances of winning it or keep the price the same and make more profit.

But for some reason, they chose to do it the way they did.

I'd really like someone to talk to a brake systems engineer @ AM G and ask them "Why this way, with the dual airpacks and such?". I'll bet he tells us something that we have not considered.

I'm not trying to flame you guys and I can see a lot of you have put a lot of time and research into this and I am sure everyone (myself included) appreciates it.

 

[emr]

Just sayin, I have lost a brake line I think 3 times in my life, I lost all brakes at these times, I have lost my brakes in the deuce by human error once left with no fluid, had the same braking I had with the trucks with split systems, no brakes, I have 40 thou on one truck alot on the others, other than human error that would have been the same result with a split system, no fluid, So I guess I am saying thet this standard system works . and since 1950 they work, I am just thinking out loud also, I am into upgrades, and part of any hobby is playing with the trucks, or anything else, so its cool to read about, and think its great, But for the average Joe, I think it should be said Enjoy your truck the way it is or anyway one can afford it, they have No known shortcomings for what they are, tactical trucks , that require maintenence, U will never put enough parts on to get away from this,...There are so many parts or funtions... like the whole truck , to make it as safe as a new one, But think I can see that is not the point here, good luck !! Just pointing out to those with less experience there is no emergency, ...Randy