Hydro-Max Brake Assist *pics added* (long read)

[elgordo371]

Just saying I feel let down! After reading 11 full pages of this thread I was thinking I was going to be reading here in the end how the end product worked and a list of parts for us all to benefit! LOL, However I did find a ton of info I am very grateful for! Thanks all.
This month I will have had my M813 for two years. Still very much want a dual circuit brake system.
The below site looks to be a good place to find the variety of parts for the following:

Backup Motor, 24V w/ Single Threaded Stud Connection and 2 Replacement Seals for Bosch Hydro-Max® Brake System

The Bosch Hydro-Max brake system operates off of power steering pump pressure, and has an electric backup motor to supply you with brake assistance in case the engine dies. The Hydro-Max has come OE on most medium trucks since the mid 80's, that aren't full air-brake, including school buses...

www.powerbrakeservice.net

From this thread I will be looking for:
1. Freight liner Hydro max unit with 50/50 proportioning (Has the Pressure differential switch to notify a warning light letting you know there is a problem, and it has a low level brake fluid sensor. See post 125 on page 7 for details)

2. Custom mount for a 2nd Stock style NHC250 Power Steering pump which I already have.
Note: I have no idea how I would get belts onto this second unit seeing there may be a need for the belt to contact more than 1/4 of the pulley to not slip when under max load.

3. 24V emergency motor for the Hydro max unit, may need the positioning adapter used in these pages, but I am hoping not to as my assembly would be mounted to the firewall not on the frame where the original air/hydraulic unit is in this thread. HOWEVER that could change .

4. Firewall mount Wilwood pedal assembly or similar (I would be getting the double peddle 7:1 mechanical advantage unit and using the 2nd peddle to install a hydraulic clutch assembly which would remove the "flex play" out of the stock linkage that annoys me when wheeling when the body and frame flex independent of each other.

5. 2" bore Master Cylinder with large reservoir.(The M813 5 ton I believe has larger wheel cylinders than the deuce and I am thinking this is going to be needed for the extra volume. However if going to disc brakes and using F750 calipers, this could be better at 1 3/4 perhaps. Still need to research.

6. Dual circuit proportioning valve External to the Master cylinder. I am not sure if this will be needed as the Freight liner MC unit is supoto take care of this so this will need more research for me... (50/50 seems best to match stock feel to the brakes)

7. Flexible brake line hoses from proportioning valve/or MC to frame rails as this M813 flexes like no other and the lines cannot be hard lined down to the frame.

8. Trailer brake mod to keep trailer brake function if I actually ever get a trailer. I already have a hand operated trailer air brake arm, which is intended to be mounted on steering column. to manually engage the trailer brakes. From what I understand this device is to manually engage the trailer brakes by themselves if desired. I was thinking this could be used to keep some way to have air brakes to a trailer. Since I do not own a trailer this doesn't seem very important at this time but someday who knows maybe I will.

9. Residual pressure valves for the brake lines. This is again a bit of a grey area as disc brake systems usually have these but any of my drum brake systems did not, but in this case it appears the Precision Re builders who are the experts leading most of the hardware options discussed here were thinking this is the right direction to go with 15lb residual pressure valves, one for each line.

Homework items, :
1HW: Seems important to know the Master Cylinder bore size on the original air/hydro-unit for the M809 series just to match that with the HYDROMAX bore size seems like a good way to go.
2HW: Anyone know what the stock PS pumps on the 809 series put out in PSI and volume? Should ensure this volume and pressure are compatible with the PSI that will be created to ensure we can get a "stock" pressure at least to the brake cylinders. On one post the psi was stated to be about 1500psi:

Hydro-Max Brake Assist *pics added* (long read)

Hi Rusty, I will back up and list what I have, then my ultimate goal... On my M135 I have acquired the following: B700 Rotors F550 Calipers HydroMax master. I will be keeping the 4 15306 brake wheel cylinder brakes on the rear as stock. Ultimate goal...

www.steelsoldiers.com

3HW: Important! I have not seen anywhere in the discussions here what type of brake fluid is to be used. Our rigs use DOT 5 which is silicone based. These Hydromax units use other types. Anyone have any info on how this is addressed? I would think I would run DOT 5 still. @jesusgatos how did you fix this?

On my M813 I would totally want at the same time to swap to disc brakes. All dreaming here. From what I have researched the F750 10 stud discs with the 4 piston calipers look like a solid fit. To do this mod I would flip my rear hubs, run long lug nut studs through the disc brake, then through the hub. I would then bolt/weld some caliper mounting plates to the axles. This way the disc and caliper will be tucked up inside the wheel and out of harms way.
A bonus from flipping the hub, is my rig with HEMTT wheels on all 6 tires are inset in the rear. Normally people put them on just the front axle to keep 16.00R20 tires from hitting quite so much on the steering box cover due to their 1 1/2 or 2" offset from stock 5 ton rims, but if you run them on all 6 the fronts are offset out from stock and the rears are inset from stock giving the rig a narrower rear tracking of the tires. I would prefer a wide track in the rear as well so flipping the hub is desired.

Your proportioning is not 50/50. On your 813 proportioning is accomplished by varying the size of the cylinders, I believe. Fronts are a different diameter from rears, unless I am mistaken.

Hydromaxes use DOT 4 or DOT 5.1, I am told. If you use pure silicone DOT 5 fluid it can cause the seals to swell.

I understand the normal way to retain air braking for trailers is to retain the stock air pack. I believe the approved procedure is to route a line from one of the master cylinder outputs to the hydraulic input on the air via a 'T' in the line. Then you plug the air pack hydraulic output port. This limits the function of the air pack to providing proportional air to the trailer brake activation glad-hand. And since the offshoot from the 'T' in one of the master cylinder outputs goes nowhere but to actuate the air-proportioning switch in the air pack, it should be neutral to the operation of the circuit.

Hope that's clear. I would confirm with Bendix whether or not the DOT 5 incompatibility is correct.

 

[goodwithwood35]

You can use multiple master cylinders with hydromax boosters. The type of fluid depends on what master you’re using. The hydromax booster runs off your power steering not brake fluid so it’s dependent on what your gearbox, pump, and hydromax is approved to run on.


Sent from my iPhone using Tapatalk

 

[elgordo371]

You can use multiple master cylinders with hydromax boosters. The type of fluid depends on what master you’re using. The hydromax booster runs off your power steering not brake fluid so it’s dependent on what your gearbox, pump, and hydromax is approved to run on.


Sent from my iPhone using Tapatalk

That's sorta true inasmuch as there is no sharing of fluids from the brake side and booster side. The issue is liability.

Bosch/Bendix explicitly specifies DOT 3 brake fluid for the master cylinder in Hydro-Max systems. Using DOT 5 voids compatibility and risks damage. So, while you could find an explicitly DOT 5 MC and mate it to a Hydro-Max, any loss of brakes that results in an accident is going to draw a great big target on whoever did not do it the way the manufacturer specified.

DOT 5 is silicone-based and can cause swelling, degradation, or failure of rubber seals, o-rings, and hoses designed for glycol-based fluids (DOT 3/4/5.1)...which includes most MCs you could buy to mate to the Booster.

Hydro-Max systems, of which the boosters are a part, are engineered for glycol fluids, which are compatible with the standard rubber materials in the master cylinder and lines.

The context of Superthermal's questions here link to the Disc Brake Engineering thread where he said wanted to do both, but prioritized the booster for the dual circuits.

The seals in the wheel cylinders in the drums are made for DOT 5. But the seals in any future disc brake upgrade almost certainly will not be compatible.

The main reason to use DOT 5 is its stability in long-term stored vehicles, and its high boiling point. Oh...and it also won't ruin paint, but given the general state of most of the paint on our vehicles, I would tend to think this isn't a top priority for most.

If your use case for your truck is long term storage with the occasional odd parade, it might be worth it to stick to DOT 5. But if that's your use case there's no reason to change your brake system at all, provided you've maintained it and kept it in good working order.

If your truck is getting frequently driven for long miles where things are more likely to happen to decades-old brake lines... then you probably should install a double circuit system for liability alone. We don't want to get another long period where surplus goes exclusively overseas like happened when the M151's were auctioned and people unaccustomed to older technology promptly rolled them and blamed their stupidity on the trucks.

I hope you can appreciate that the comparatively 'light' Deuces are 13,000-15,000 pounds dry. And a dry M813 is 18,000-22,000 depending on what is on it. In a runaway condition it will turn F350s into unidentifiable scraps, and roll over or through most passenger vehicles without even slowing much. And a 923 isn't much different than the 813 in that regard. Those would be accidents far more controversial than the M151s ever were.

So, if you want to drive it frequently, or for work, (and to be clear if you want them to really last they need work), or even for play that requires much time on modern public roads, it is incumbent on all of us to protect each other, civilians, and the community by doing things in a defendable way.

You can justify a 70 year old truck in a VFW parade losing brakes, and damaging someone's float. The same would not be true losing brakes on I80 screaming downhill through a canyon flattening Subarus and Priuses, unless everything is done to spec, inspected, and pre-emptively approved by DOT or Highway Patrol.

So, you have to ask yourself. When you get new soft brakelines, "Are these 40 year old New Old Stock? Are they still good with or without DOT 5?" And if you are having new soft brake lines made you need to ask, "Did the guy who made them know these need to be from the DOT5-compatible hose? Or did he probably just grab the same hose he probably grabs for over 90% of his other work? And if he did, then is my hose going to swell and lead to one or more wheels (or axles if still on drums) losing all braking?"

While I like DOT 5 in my Army motorpools where the main enemy is usually disuse, if I'm putting those trucks on I95, I80, I10, I5, or I15 for more than 40-50 hours per year, without the Army standing behind me for liability, then I am going to make my brakes as much like most of the other similarly sized trucks on the road as I can, and then I am going to get the authorities to approve it, for my own peace of mind and the community's.

And that's the issue. If your use is occasional, recreational, or contained on farmland, then there is absolutely nothing wrong with the system that is on the truck, no reason to make any changes at all.

I use my Deuce frequently here in the Fort Bragg area to help members of my church cut up and haul away fallen trees. This past summer I was going down a winding two-lane road with a load of wood at a 45-50 MPH, when a guy in an obviously just-restored squarebody chevy turned right out in front of me. If my brakes were not 100% I would have T-boned him. I locked up all 10 wheels, and the old girl came to a rapid stop. After I treated him to a selection of the language that the Army has not allowed in the past 20 years, I gave his resto-mod a thumbs up and wished him a fine day.

Reasons to make the change include:
Unavailability of Original Spec Parts
New manufacture parts made to incorrect specs
Frequent use on public roads
Bigger Tires that require more pressure/ better heat dissipation
Big loads
AND HERE'S THE CONTROVERSIAL ONE - You can't afford the Army solution, which always was and remains MORE CHECKBOXES ON THE MAINTENANCE SCHEDULE.

If you ACTUALLY follow the TM's full maintenance schedule on your truck, as an individual owner you will do little else. I am not guessing here. Your lube order specifies between 30 minutes to an hour DAILY just to inspect for proper lubrication, and 3.5 hours to do lubrication for every 1,000 miles driven.
People forget that there are specified Monthly, Quarterly, Semi-Annual services to be done even if you don't drive it in that time period. Specifically, the manuals specify that it must get a checkout drive semi-annually.
They also forget that the brakes are supposed to be adjusted and the axles bearings re-packed with GAA semi-annually.
The point is that if you can't do it the way the TM calls for, then you need to make some changes to the equipment the TM is referencing such that you can comply with the new equipment manufacturer's recommendations, or simply accept risk.