Dual-circuit Hydromax brakes on M35A2, good air diagram needed.

[fungus]

Hi all,

I've been doing some digging and some great information is available on the site for prior conversions. A gentleman had done a hydromax conversion in the past from a unit pulled from an International S1700 IIRC, but he tied both circuits together and fed the original single brake line. spicergear's thread link

I am getting a system from a 2003 International 4300 that I am going to _try_ to put underneath the cab using the original deuce brake pedal and lever. Just in case, I'm also snatching the brake lever assembly from the 4300. In the event plan A doesn't pan out, plan B is to firewall mount it.

Toward the rear of the truck, just behind the airpack is a splitter. The back half feeds the back two axles, the front half feeds the front axle. I intend to route circuit A to the front axle and circuit B to the rear.

*nipping the bud*
Before anyone starts freaking out about proportioning valves, remember that the single circuit system routes equal pressure across all slave cylinders. Also remember that a dual circuit master cylinder will independently provide the VOLUME of fluid necessary to create the PRESSURE required in both circuits. In other words, if you command 1500PSI with your pedal, you should get 2x the fluid VOLUME in the rear circuit (4 slave cylinders) vs the front circuit (2 slave cylinders), leading to 1500PSI+/- in both front and rear. All slave cylinders should see the same pressure.


You can see the spoken of fitting here, just under FL2:

DEUCE BRAKE LINE REFERENCE GUIDE (Sizes, lengths, fittings)

POST 1~ SINGLE CIRCUIT BRAKE LINES POST 2~ DUAL CIRCUIT BRAKE LINES POST 3~ BRAKE PARTS REFERENCE GUIDE POST 32~ BRAIDED STAINLESS FLEX LINES/HOSES POST 40~ DUAL CIRCUIT MASTER CYLINDER BRACKET INFO & CAD FILE SINGLE CIRCUIT BRAKE LINE INFO I've been selling Stainless Steel Braided Flex hose...

www.steelsoldiers.com

Since I will be ditching the air booster and single-circuit master cylinder, I need to ensure the other air-operated items are still properly supplied. I would like to keep compressed air on the rig for the sake of tools and the occasional air brake trailer I need to jockey (not to use the brakes, just to keep from having to cage them all).

The following diagram has a complete system, but has very little markup. Additionally it seems to show hydraulic (brake) lines as well as pneumatic lines with no differentiation.

https://www.steelsoldiers.com/attachments/m35a2airdiagram-jpg.741707/

Does anyone have a better pneumatic system breakdown that identifies the individual components? I seem to even have air lines going to the fuel tank, I have no clue what's going on there.

For the uninitiated, the Hydromax system uses the power steering pump to provide boost rather than compressed air or vacuum. In addition, it has a backup electric pump that will provide that "last effort" braking in the event of engine failure. It's a very robust, modern system with plenty of failsafe. If you're already going the power steering route, it seems like a win to make this jump as well. I'm biting the bullet up front, as I need to overhaul/replace the booster and master cylinder. By piecing things together, this is a cheaper system than rebuilding/replacing the OE air-assist parts.

 

[fungus]

I found an itemized air pressure diagram!

trailer air brake operation

I took a quick look under my truck the other day, and it looks like the modulated air supply to the trailer gladhand comes off the airpac, not the master or valve on the pedal system. Is it safe to assume then that a hydraulic circuit failure on the truck could also potentially stop the booster...

www.steelsoldiers.com

 

[G744]

Brake failures are seldom encountered, when the truck gets regular maintenance on the original air-over-hydraulic system.

It worked well for many years on these trucks, and I've never had a failure on my 5 tons.

 

[fungus]

Hi G744, I agree with you. I could do a complete overhaul from pedal to wheel cylinders and a regular PM cycle, then I would be comfortable with the stock brakes. The problem I have is parts availability, price and failsafe. We live in a VERY rough area and will regularly be pushing this truck to its limits hauling gravel. There's not a level surface here for miles. I need something I can get parts locally for and depend on to limp home.
There are two camps of people here, probably with different needs. One says the old brake system is fine with proper maintenance. The other says it needs to be upgraded to a modern system with failsafe. Both are right.
For our curvy, windy, narrow gravel and dirt roads here, hauling full capacity in gravel, I need some steering assist and brakes with failsafe.
Hydraulic assist steering and hydraulic assist brakes will go hand in hand for me, so I'm knocking them both out up front.

 

[rustystud]

Hi G744, I agree with you. I could do a complete overhaul from pedal to wheel cylinders and a regular PM cycle, then I would be comfortable with the stock brakes. The problem I have is parts availability, price and failsafe. We live in a VERY rough area and will regularly be pushing this truck to its limits hauling gravel. There's not a level surface here for miles. I need something I can get parts locally for and depend on to limp home.
There are two camps of people here, probably with different needs. One says the old brake system is fine with proper maintenance. The other says it needs to be upgraded to a modern system with failsafe. Both are right.
For our curvy, windy, narrow gravel and dirt roads here, hauling full capacity in gravel, I need some steering assist and brakes with failsafe.
Hydraulic assist steering and hydraulic assist brakes will go hand in hand for me, so I'm knocking them both out up front.

For someone who is going to use their truck on a regular basis and don't need a stock Deuce or even a military truck I would just buy a good running 2 to 3 ton truck and put the Rockwell axles under it.
Save yourself a ton of money and grief.

 

[fungus]

I value the opinion, but bear in mind that I'm saving money by switching to the hydromax system. I need to do a complete overhaul of the airpack and master cylinder, very likely needing to replace the master.
C'mon fellas, humor me I'm not trying to start a war, just documenting my swap for those who wish to do something similar.

 

[rustystud]

I value the opinion, but bear in mind that I'm saving money by switching to the hydromax system. I need to do a complete overhaul of the airpack and master cylinder, very likely needing to replace the master.
C'mon fellas, humor me I'm not trying to start a war, just documenting my swap for those who wish to do something similar.

I'm not trying to start a war but give you good honest advice here. In all honestly, just putting the Rockwell axles under a good running 2 to 3 ton truck would "save" you a ton of money . I've seen it done several times now and the trucks came out great. Good brakes, good transmission, and a modern cab with heat and A/C . What's not to like ? You could sell off the rest of the M35 to other military truck buffs and recoup some money.
In fact, I'm saving a set of "Rockwells" right now for just that type of conversion.
Of course mine is going to be a small bus and not a truck, but it's the same concept.

 

[fungus]

Well, I don't know if I can be considered a "military truck buff", I've only been keeping my eyes peeled for a decent condition deuce for about 10 years. I also am not sure what criteria go into "needing" a military truck.
-If it's a question of purist restoration vs modification, I'm always heavy into modification territory.
-If it's a question of using the truck for what it was meant for, I'm doing just that; hauling heavy loads into low-speed, rough terrain.
I'm not building a rock crawler that hauls barely a case of beer.
I'm not bobbing it and putting on huge singles.
I'm making it easier to steer with a busted shoulder and getting a little redundancy and failsafe in the braking system. I drove a dump truck for years with single circuit brakes, there's no way I'll do it again.
I have hundreds of gallons of waste motor oil waiting for this multifuel. I barely go over 35 mph back where we live. What I'm doing is perfect for a _near_ stock deuce.
Adapting the Rockwell axles to a more modern truck sounds like way more work than adapting a newer master cylinder and booster to me.

I mean no offense to anyone here. We all have our opinions, experiences and priorities. As an opinion, I think it's pretty goofy to drive around a 2.5ton truck empty... But that's an opinion

If anyone wants to hear my story of why this thing works extremely well for our purposes off-grid at the end of the dirt road, PM me. I'm happy to share pictures of the road building. This thread is for the sole purpose of documenting a proper dual-curcuit hydromax retrofit for cheaper than stock parts replacement.

For the "why", I can start another thread.