Dual Circuit Brake Engineering Thread

Heath_h49008

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I'm coming from the automotive industry here, so be kind if I'm missing some thing...

We are trying to split the system in a manner similar to modern automotive brakes... single reservoir feeding two brake circuits so a line failure in either one won't disable the other. Correct?

The only thing stopping you is the current MC design vs the modern, and the volume of fluid a modern replacement could push, and with what pressure.

If the air pack functions in the same manner as a vacuum booster, applying additional force to the piston shaft upon brake application via air pressure, then we don't need to talk about it. We have the booster...

So, from what I can tell, we need a dual chamber piston master cylinder capable of pushing 1/3 fluid volume to the front, and 2/3 to the rear, at the same pressure (or marginally more)... and an adapter capable of allowing us to bolt this to the existing bracket and airpack. Brackets are easy... steel, welder, time. But what common modern vehicle with hydraulic drum brakes of similar wheel cylinder size and dual rear axles should we look at for the donor MC?

The easy answer would be to simply make a new master cylinder and piston with the correct dimensions and dual circuits... is that something we might consider? A second version for the bobbers might also be useful.
 

Heath_h49008

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Just doing some looking... it seems a lot of old dump trucks used to be hydraulic brakes... any tandem axle hydraulic brake system from the 1970s drum dumps would seem to be a good place to look. I know the old F800 we had was a single axle, but did they make them in tandems as well?

I'm being dumb... Disc brake master cylinders run higher pressures than drums... (if it can handle the volume required) the pressure produced is no big deal. The Wheel cylinders and lines should have no problem dealing with the increase either. They may just seem a bit "touchy" if you don't put something on to moderate it.

So, unless I'm missing something basic, this opens the door to a LOT of master cylinders.
 
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73m819

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What would need to be done to go SUPER size duel brakes for the 5Ts
 

Heath_h49008

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What would need to be done to go SUPER size duel brakes for the 5Ts
It looks like Uncle Sam just built split REDUNDANT brakes on the late Air Force trucks... kinda makes sense. Same parts and all, just two of them.

If there is a big enough master cylinder to work for the M35series, it may well work for the 5ton.

The trucks I'm checking right now are old GMC and Ford 1970s dump trucks and more modern stake trucks. My only real concern is the volume required for the tandem rear axles. On a Bobber it's gravy.
 

73m819

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It looks like Uncle Sam just built split REDUNDANT brakes on the late Air Force trucks... kinda makes sense. Same parts and all, just two of them.

If there is a big enough master cylinder to work for the M35series, it may well work for the 5ton.

The trucks I'm checking right now are old GMC and Ford 1970s dump trucks and more modern stake trucks. My only real concern is the volume required for the tandem rear axles. On a Bobber it's gravy.
With the proper Big M/C, just adding another 5t airpack alone with rerouting the brake lines, ought to do it, I was thinking of front and one #2 axle brake, other #2 axle and rear axle split ?????
 

Heath_h49008

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With a 5ton you have hydraulic power for a hydroboost system as well... it opens a lot of doors. Building a bracket and just adding parallel systems seems like a waste though. One large system of modern design should more than do the job. We aren't going to do much with more pressure, the current one can lock the brakes. If we need more bakes, we have to look at the friction surfaces. If we just want to split them for safety in case of failure, we should be able to do that with just the right master cylinder.

At least that's what I'm thinking... I could be wrong!
 

turnerman

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I have a dual brake truck i will sell you and then you don't have to worry about the parts. I converted an older deuce with a c6500 truck with hydro boost. That was an ordeal.
 

clinto

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Has anyone solved the issue of how to mount the PTO linkage when doing the dual circuit upgrade? Thanks.
If you are using the factory 1987-1989 parts (the cast mount for the master cylinder) it has an ear/boss for the pto linkage to attach to. You will not use the stamped pto lever mounting bracket like the older trucks use.

See: http://www.steelsoldiers.com/deuce/23134-winch-lever-mounting.html

I thought there was a pic somewhere on the site showing this, but I can't find it now. If someone wants to see it, I can shoot it this week, as I just added a winch to my '87 USAF A2C.
 

dilligaf13

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I'm not sure on the year of the donor truck but it is a late 80's USAF truck. I'm not seeing the ear for attaching the PTO. If you could grab a picture that would be much appreciated. That link was also very helpful. Thanks.
 

Kohburn

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I'm coming from the automotive industry here, so be kind if I'm missing some thing...

We are trying to split the system in a manner similar to modern automotive brakes... single reservoir feeding two brake circuits so a line failure in either one won't disable the other. Correct?

The only thing stopping you is the current MC design vs the modern, and the volume of fluid a modern replacement could push, and with what pressure.

If the air pack functions in the same manner as a vacuum booster, applying additional force to the piston shaft upon brake application via air pressure, then we don't need to talk about it. We have the booster...

So, from what I can tell, we need a dual chamber piston master cylinder capable of pushing 1/3 fluid volume to the front, and 2/3 to the rear, at the same pressure (or marginally more)... and an adapter capable of allowing us to bolt this to the existing bracket and airpack. Brackets are easy... steel, welder, time. But what common modern vehicle with hydraulic drum brakes of similar wheel cylinder size and dual rear axles should we look at for the donor MC?

The easy answer would be to simply make a new master cylinder and piston with the correct dimensions and dual circuits... is that something we might consider? A second version for the bobbers might also be useful.
exactly - all we really need is to know the bore and stroke of the single master cylinder. then we can properly size a dual chamber master cylinder and fab up a simple mounting adapter. then add a second air-pack and run the brake lines. done.
 

Bcurtman

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This is also how I saw it, but my thought was trampled by those who said we MUST have two air paks. Line to the front, line to the rear, fed from a single master cylinder with two fluid chambers. Doesn't seem like rocket surgery. Are we worried about a hydraulic failure or an air failure-or both? Is there a mechanical pushrod from the air pak to the master? If not, then that may be an issue. But loss of air would then still render both systems in operative. I was Maintenance Supervisor and Engineering Manager for the largest disc brake plant in the world for 12 years, but that doesnt qualify me as a brake designer. However, I've wrenched on vehicles as a hobby all my life, owned 46 jeeps, and converted numerous to upgraded brake systems.
 

peashooter

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I'm coming from the automotive industry here, so be kind if I'm missing some thing...

We are trying to split the system in a manner similar to modern automotive brakes... single reservoir feeding two brake circuits so a line failure in either one won't disable the other. Correct?

The only thing stopping you is the current MC design vs the modern, and the volume of fluid a modern replacement could push, and with what pressure.

If the air pack functions in the same manner as a vacuum booster, applying additional force to the piston shaft upon brake application via air pressure, then we don't need to talk about it. We have the booster...

So, from what I can tell, we need a dual chamber piston master cylinder capable of pushing 1/3 fluid volume to the front, and 2/3 to the rear, at the same pressure (or marginally more)... and an adapter capable of allowing us to bolt this to the existing bracket and airpack. Brackets are easy... steel, welder, time. But what common modern vehicle with hydraulic drum brakes of similar wheel cylinder size and dual rear axles should we look at for the donor MC?

The easy answer would be to simply make a new master cylinder and piston with the correct dimensions and dual circuits... is that something we might consider? A second version for the bobbers might also be useful.

Ive got a 88 AF truck with the split brakes, I havent read through this whole thread so Im not sure if its already been said or not but besides the extra airpack, different master cylinder, differential valve & warning light, one of the air tanks is 2 chambered for some reason (so there are a total of 3 drain valves on these trucks' air tanks)
 

m-35tom

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right, it has already been done! why reinvent the wheel, just copy the AF truck system. unless you want to make it better (imho) which is what i do to my trucks with full air over hyd.
tom
 

clinto

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I'm not sure on the year of the donor truck but it is a late 80's USAF truck. I'm not seeing the ear for attaching the PTO. If you could grab a picture that would be much appreciated. That link was also very helpful. Thanks.
Ok, the green hardware is the older truck-it's clintogf's '69 A2 with the single circuit brakes. You can see that the PTO shift lever is sandwiched in a stamped steel mounting bracket that bolts onto the side of the single circuit master cylinder via two cast bosses which are threaded/


The tan hardware is attached to my '87. You can see the cast mounting bracket that the master cylinder bolts to includes an "ear" for the PTO shift lever to attach to. Give those AM General engineers credit, as the original PTO shift lever works with the new mount-i.e. they designed the mount around the old style lever so there would be one lever for both mounts. Pretty clever.
 

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Heath_h49008

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Ive got a 88 AF truck with the split brakes, I havent read through this whole thread so Im not sure if its already been said or not but besides the extra airpack, different master cylinder, differential valve & warning light, one of the air tanks is 2 chambered for some reason (so there are a total of 3 drain valves on these trucks' air tanks)
I was waaaaayyyy off when I wrote that.

The M35A2 uses the airpack to directly boost fluid pressure. One would be required for each circuit and a two port MC with divorced pressure zones.

Running hydroboost with a single booster is possible, but that would require the MC be able to move enough volume in each circuit, as well as have roughly a 50/50 split. As well as plumbing the hydraulic lines/pump for the booster itself.

Unless you happen to have some fabrication skills and tools, as well as nearly free parts that fit the bill, it would be cheaper and safer to re-create the Air Force split system rather than build one from scrap. IMHO

You need the right MC/mount, another airpack, and the lines are simple to whip up as would be the airpack bracket. There might be junkyard options if the correct MCs are hard to find, but I don't think there is any shortage. Splitting the air system too is a nice idea, but not technically required. (Most people being more concerned about hydraulic failure rather than air pressure loss)

Sorry about that first post... I cringed reading it. :oops:
 
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