Dual Circuit Brake Engineering Thread

Eastern Surplus has the master cylinder but it's very pricey. I really want to put the AF system on my 109 when I rebuild the brakes.

Suscribed, Like the idea( if not the cost) of putting a dual circuit on my truck.

Jesse6325 said:

Suscribed, Like the idea( if not the cost) of putting a dual circuit on my truck.

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The simple answer is: if it was as easy as everyone says-they would have it and they don't!

Tdual circuit brakes

Too true, I guess that means I'll just have to maintain my single circuit brake real good.

Has anyone considerd using 105 trailer mc and air pancake? All that would need to be done is plug the line to one axle then mount and plum the 105 parts to it. Would not be hard to do parts are easy to locate. Then you have brakes on at lest one axle. But thoughts in my head don't always work.

Is using 105 parts such a bad idea no one wants to comment? Something I'm not sure of is if the line pressure from the 105 mc would be about the same as th deuce? Although it is a system designed to work with the deuce. You would just be moving it from the trailer to one truck axle.

housemover said:

Has anyone considerd using 105 trailer mc and air pancake? All that would need to be done is plug the line to one axle then mount and plum the 105 parts to it. Would not be hard to do parts are easy to locate. Then you have brakes on at lest one axle. But thoughts in my head don't always work.

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housemover said:

Is using 105 parts such a bad idea no one wants to comment? Something I'm not sure of is if the line pressure from the 105 mc would be about the same as th deuce? Although it is a system designed to work with the deuce. You would just be moving it from the trailer to one truck axle.

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If I am reading your idea correctly, you're suggesting that one circuit of the deuce's brakes would be operated by the "pancake" and master of the M105?

Here's why no one would do that:

1. You lose mechanical connection to the braking-right now, a deuce will operate it's service brakes in the event of catastrophic air loss. Go move your deuce around in the yard and leave the air system open so it can't build pressure. It's scary and dangerous, but you can stop it. In your plan, a catastrophic air loss would mean no braking on the m105-system circuit.

2. I would bet dollars to donuts that the one system working in the stock setup and the other using air to activate the master cylinder would output different brake fluid pressure, thus creating an uneven braking situation.

3. Is the M105 pancake a booster, or an actuator? The deuce airpack acts as a brake booster, significantly increasing the brake pressure output. Does the pancake do the same, or does it simply actuate at a 1:1 ratio? I don't know this one, it's a genuine question.

4. Finally-the military already had ALL those M105 parts in the system-if that idea would work, why would they have spent the money to have AM General go through the effort of casting an whole new master cylinder mount, create a new master and plumb in a second airpack?

clinto said:

If I am reading your idea correctly, you're suggesting that one circuit of the deuce's brakes would be operated by the "pancake" and master of the M105?

Here's why no one would do that:

1. You lose mechanical connection to the braking-right now, a deuce will operate it's service brakes in the event of catastrophic air loss. Go move your deuce around in the yard and leave the air system open so it can't build pressure. It's scary and dangerous, but you can stop it. In your plan, a catastrophic air loss would mean no braking on the m105-system circuit.

2. I would bet dollars to donuts that the one system working in the stock setup and the other using air to activate the master cylinder would output different brake fluid pressure, thus creating an uneven braking situation.

3. Is the M105 pancake a booster, or an actuator? The deuce airpack acts as a brake booster, significantly increasing the brake pressure output. Does the pancake do the same, or does it simply actuate at a 1:1 ratio? I don't know this one, it's a genuine question.

4. Finally-the military already had ALL those M105 parts in the system-if that idea would work, why would they have spent the money to have AM General go through the effort of casting an whole new master cylinder mount, create a new master and plumb in a second airpack?

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I agree no air pressure and you still have brakes sorta. But blow a line or mc or wheel cylinderand your done. Been there and that was no fun and I stay up on my pm's.

Different pressures something I have thought about but I keep thinking the 105 was designed to work with the deuce system

Agree dual airpacks are the better system UNCLE spent way more time and knowledge on it than I have. But those systems are hard to come by.

All in all I'm not willing to try it just to see if it works without more input. I had one run away 14,000# rocket not a enjoyable experiance and I don't care to repete. Thats why I'm thankful for this site its saved me from myself numerous times.

Since this would be some very pertinent information on improving a deuce's, I will pose a question to the more knowledgable here. The 2002 Dakota that I have has a dual circuit system where the front driver and rear passenger brakes are on one circuit and vice-versa for the other circuit. Would it not make sense to do a similar setup so that the pressure and volume for brakes are equal throughout the system. I.E. front driver, center passenger and rear driver on one circuit. I think that this would make loss of one circuit more manageable since the braking is more-or-less evenly distributed throughout the weight of the vehicle.
Thanks in advance for reading and offering up a more experienced opinion.

That's what I'm doing to my bobbed deuce as we speak. The M105 has 4 wheel cylinders, the same as the 4 of the rear axles of a deuce. I'm putting a pressure regulator in line of the air from the relay air circuit, so I can adjust the pressure to the pancake/air motor. I'm also putting a valved tie between the front an rear hydro circuits in case one or the other fails and I can use the other to get home. I'm mounting the MC/air motor under the bed, at the rear, above the axle and running the vent to the air box up front. The 105 has a payload of 5000 lbs on a single axle with 4 wheel cylinders, my thought is the 4 cylinders of the 2 axles of a deuce should be controllable with the air regulated creating a second circuit.

dilligaf13 said:

Has anyone solved the issue of how to mount the PTO linkage when doing the dual circuit upgrade? Thanks.

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Here is another pic of the master cylinder bracket with the pto handle.

I have some new split circuit master cylinders w/reservoir for the late 80's air force trucks (not the a3 style). Pm me if you need one.

I'm not sure if there are many people still interested in adding dual circuit brakes to their trucks but I'll throw this out there also. Besides having a couple exact replacement M/C for the 87-89 trucks shown in the post above, I also have some units that are an identical match that also include the built in differential valve (which alerts you to a failure of 1 circuit).

I spoke with Kyle at Blackrockfab.com (blackrock) a while back about making the master cylinder bracket also. I haven't gotten my hands on a spare one to send him yet but if anyone has one they can part with for a while, let him or I know. He will try to duplicate it in a affordably priced weldment for folks looking to do a conversion. (would fit a2 trucks w/winch and w/o winch).... you would still need a second air pack and either a 3rd air tank or a dual chamber air tank off an A3 truck though.

peashooter said:

I'm not sure if there are many people still interested in adding dual circuit brakes to their trucks but I'll throw this out there also. Besides having a couple exact replacement M/C for the 87-89 trucks shown in the post above, I also have some units that are an identical match that also include the built in differential valve (which alerts you to a failure of 1 circuit).

I spoke with Kyle at Blackrockfab.com (blackrock) a while back about making the master cylinder bracket also. I haven't gotten my hands on a spare one to send him yet but if anyone has one they can part with for a while, let him or I know. He will try to duplicate it in a affordably priced weldment for folks looking to do a conversion. (would fit a2 trucks w/winch and w/o winch).... you would still need a second air pack and either a 3rd air tank or a dual chamber air tank off an A3 truck though.

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Hello Peashooter, The bracket idea sounds great! In fact I'm on that like white on rice ! By the way, what is the price on the master cylinders ? Thanks.

rustystud said:

Hello Peashooter, The bracket idea sounds great! In fact I'm on that like white on rice ! By the way, what is the price on the master cylinders ? Thanks.

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The stock replacement is about $300, the "upgraded" one would be a hair more since it has a built in differential (failure warning) switch.

Subscribed, and sold on the idea completely. Thanks to frodobaggins for starting the thread.

But I do not have a degree in mechanical or automotive engineering. Just a guy with a truck, motivated and willing.

So as long as it can be spelled out and enumerated part-by-part (which this all seems to be approaching closer-and-closer).

No new ideas?

I found out that all the 1987 to 1989 M35A2C trucks came with the bracket to mount a PTO handle. Here's some pictures.
Thanks Peashooter.

Anybody ever give up a spare bracket to have re-popped by Blackrock Fab?

Interesting thread. I used to upgrade my old VW Buses to dual circuit MC's but they are a different animal altogether. In the Deuce having the backup circuit seems a very important upgrade and one that I will definitely be looking in to.

Docluvstrucks said:

Anybody ever give up a spare bracket to have re-popped by Blackrock Fab?

Interesting thread. I used to upgrade my old VW Buses to dual circuit MC's but they are a different animal altogether. In the Deuce having the backup circuit seems a very important upgrade and one that I will definitely be looking in to.

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A member has one for me that I will model up in 3D CAD and make drawings available to all. I'll also send the bracket to Kyle @ Blackrock to see if he can duplicate affordably. The member hasnt been able to get it completely removed from the truck yet however. If anyone else has one available please feel free to send it to him. I dont need one but was just trying to help out those who want one.