Split brake system

[peashooter]

right, the trucks (87-89 deuces) dont have a proportional valve but they do have a split ratio master cylinder so more fluid goes to the rear circuit (rear 2 axles) and less fluid to the front circuit (front axle).

The valve that many call a proportional valve on these trucks is actually a Differential valve. It isnt needed for braking, but it is was detects a failure of one circuit and then switches on a warning light so the driver knows there is a problem.

You can get these differential valve switches from the parts guys like TNJ Murray, and the likes. Outcast and I are both using a special master cylinder that meets all the specs of the original 87-89 deuce but it has a built in differential valve warning switch which eliminates a couple exra brake lines and fittings. It can mount like the stock one with the reservoir under the floor boards, or with a remote mounted reservoir on the firewall.

 

[skinnyR1]

Excellent info Peashooter and Outcast, thank you! PM sent to peashooter

 

[JasonS]

Lost brakes all at once. I am installing split master cylinder, split air tank, second air pack, and the needed brackets. I do not know of a proportioning valve in the system, however, you will need a pressure differential switch. I believe Peashooter might be able to help you out with that. I'm still sourcing parts as money allows. I'm in no way an expert on the brake system, still learning but this is what I think I know. Hope this helps.

Out of curiosity, what caused the failure?

 

[outcast]

Out of curiosity, what caused the failure?

As I remember it looked like the seal failed. I had the truck on jack stands with that drum off, had just replaced axle seals. We had some friends over and I two playing in the cab. If one of them had pushed the brake peddle it could have perhaps unseated the seals in the wheel cylinder. My bad I did not check closer. Anyway that's what I think may have happened.

 

[skinnyR1]

As I remember it looked like the seal failed. I had the truck on jack stands with that drum off, had just replaced axle seals. We had some friends over and I two playing in the cab. If one of them had pushed the brake peddle it could have perhaps unseated the seals in the wheel cylinder. My bad I did not check closer. Anyway that's what I think may have happened.

Thank you for the clarification. Sounds like more than likely someone hit the brake pedal without the drum on and it overextended the cylinder blowing it out. I have done that before too on error.It slightly diminishes my fear of complete failure of the brakes while driving. I am led to believe that you will have a brake pump or two to the floor with single circuit brakes before complete failure, while all of the fluid is being pushed out. After that, you will have nothing there.None the less, I am actively sourcing parts for a split system.

 

[mudguppy]

... I am led to believe that you will have a brake pump or two to the floor with single circuit brakes before complete failure, while all of the fluid is being pushed out. After that, you will have nothing there. ...

standard hydraulic theory says that if you have a failure on a single circuit, then there won't be any ability to build pressure in the rest of the circuit. Therefore, a truly blown wheel cylinder may in fact allow fluid to escape without enough residual pressure to provide much, if any, braking force in the remaining cylinders.

The most likely failure would be either a ruptured line or blown cylinder seal - would these typical failure conditions result in ~0 psi? Ruptured line, probably. Blown cylinder seal, eh, dunno...

 

[rustystud]

standard hydraulic theory says that if you have a failure on a single circuit, then there won't be any ability to build pressure in the rest of the circuit. Therefore, a truly blown wheel cylinder may in fact allow fluid to escape without enough residual pressure to provide much, if any, braking force in the remaining cylinders.

The most likely failure would be either a ruptured line or blown cylinder seal - would these typical failure conditions result in ~0 psi? Ruptured line, probably. Blown cylinder seal, eh, dunno...

Mudguppy your right. There will be NO pressure in your system if you have a ruptured hose or blown seal or busted line. I told this story before, but it is worth repeating. I owned a 1954 Chev. truck. I got it from my father. I drove this truck everywhere ! It was the first vehicle I ever owned. One day is was driving about 30mph or a little faster ( I was young then ! ) going down hill. I had to stop ahead so I applied my brakes. After a few seconds my brakes went totally away ! The pedal went to the floor ! I tried my emergency brake ( remember this is a 1954 Chev. ) it barely slowed. So I rammed my truck into the hillside curb and prayed ! I did come to a stop, but I needed to clean out my pants . After I got the truck home, I found a small hole in the brake line ( 1/16" ) . The inside of the lines was totally rusted out . The outside looked fine ! I also had replaced the fluid and bleed out the system months earlier. It was my first vehicle so I had replaced everything ! Belts, hoses, oils, you name it . After this experience I went to Silicone brake fluid and made sure my brake lines where always in top shape. In fact most of my vehicles have stainless brake lines, and braided stainless Teflon flex lines. That also why I'm using "Peashooter's" lines and hoses on my Duece. All this to say, when you lose the integrity of your brakes on a single circuit system, you lose everything NOW !

 

[Robo McDuff]

Looking into the hydro fuses as first step to make our 5-ton M51A2 more safer. Those remarks are in a different thread about a 5-ton dual system. The first post is more general, the next post gives some links to hydro fuses.

 

[hbrazell0003]

I know this thread is old but i would like to know how this new split brake systems has been working for the past 9 years. IS it a pain to install? I would love to do something like this on mine.

 

[Kwaligura]

I'm going to try something on my off road only deuce. A triple master cylinder setup under the floorboard just like the stock system but 3 master cylinders in a row all being pushed by the pedal at the same time. One master cylinder per axle. Just ordered them today. I won't have power assist but it is an experiment. I regularly drive trucks that are close to or over 80,000lb and know how to look ahead and increase my following distance for road conditions and idiots encountered.

 

[Another Ahab]

I'm going to try something on my off road only deuce. A triple master cylinder setup under the floorboard just like the stock system but 3 master cylinders in a row all being pushed by the pedal at the same time. One master cylinder per axle. Just ordered them today. I won't have power assist but it is an experiment. I regularly drive trucks that are close to or over 80,000lb and know how to look ahead and increase my following distance for road conditions and idiots encountered.

Just curious (and plain don't know much):

- So what is the principle behind the one cylinder-per-axle set up, less effort from the brake pedal?

 

[gimpyrobb]

Doubtful, the booster is there to overcome the pressure required to move the wheel cyls.

I'd bet this is for a better split brake system in case of a failure.

Not sure it will work with out assistance though.

 

[rustystud]

Doubtful, the booster is there to overcome the pressure required to move the wheel cyls.

I'd bet this is for a better split brake system in case of a failure.

Not sure it will work with out assistance though.

Total agreement here. I don't know why anyone would want to go to that much expense when the Air Force deuce dual brake system works great.

 

[Kwaligura]

I can do the multi master cylinder setup for less than $200. The Ford F800s were manual brake 15 inch drum systems. But were also single circuit systems. I have had a brake failure already. I didn't like it. The jeep Cherokee that stopped me liked it even less. I'm wanting to have a more reliable system. If one fails it still has more.

 

[rustystud]

I can do the multi master cylinder setup for less than $200. The Ford F800s were manual brake 15 inch drum systems. But were also single circuit systems. I have had a brake failure already. I didn't like it. The jeep Cherokee that stopped me liked it even less. I'm wanting to have a more reliable system. If one fails it still has more.

Like I posted, go with the "dual brake" system the Air Force deuce's used. It is a true split system and has worked great for decades now. One "dual" master cylinder (just like modern trucks today) with two brake boosters. The boosters put out over 800 PSI . More then any brake wheel cylinder system needs.

 

[Kwaligura]

I'm not saying that it doesn't work great but for the expense of it I'd be better off parting out the truck and buying an air force deuce. Since the air pack that is on mine is not working.

 

[rustystud]

I'm not saying that it doesn't work great but for the expense of it I'd be better off parting out the truck and buying an air force deuce. Since the air pack that is on mine is not working.

Your going to have some major expenses if you try and go with a three axle system to. Plus this is something that has never been done before, so there is going to be "Research and Development" expenses added on. Just saying, this could get extremely expensive really fast !

 

[Nomad1]

As far as item 14 is concernered do they mean the hole assembly including the bracket the master cylinder bolts to?Is the a3 bracket the same as the 87 airforce trucks that had split brakes or does the bracket in the airforce trucks make it so you don't have to drill a new hole in the floor?

See this pic from the TM mentioned above. Note all the stuff with asterisks...that's all new stuff, plus all of the plumbing. It's all really tight in there too...just FYI.

 

[peashooter]

That diagram is a bit misleading. There is a different master cylinder bracket that isnt listed on it so you can assume that they meant the whole assembly. The a3 trucks have a similar mc bracket to the airforce trucks but not identical (af trucks have a winch lever capstan and provisions for the clutch shaft to go through the bracket). The brake pedal and linkage are different on the af trucks than the a2 trucks, but it may be the same as the A3, im not sure.