modern dual circuit air over hydraulic brakes

[patracy]

The guy in that vid, IIRC, is running the electric backup pump as his sole booster.

The electric pump is a backup in the event there's no pressure from the PS pump. In that video I could see the hyd. line feeding into it. And he had a waterloo PS setup, so I'm sure he had the hyd hooked up.

 

[Dbluff]

There isn't one. Due to the space allowed in the area. And the bracket design. Then you still have to deal with a second airpack.

ok. Intresting with dual tanks and such, a splitter or something would not accommodate since you already have an airpack onboard.

 

[patracy]

ok. Intresting with dual tanks and such, a splitter or something would not accommodate since you already have an airpack onboard.

No, because you'd have to route both brake lines into a single line if you only have one airpack. The air system and tanks are just to supply air to the airpacks.


Edit:
Here's a diagram from the brake line side of things and how the normal system works. 21-23 is the line out of the single circuit MC. That feeds into the airpack shown below. The output of the brake fluid is from 22-23 which feeds out to the tee 30 that then feeds the front and rear axles. You'd need a second air pack to plumb up things to keep a dual circuit MC dual. You'd do away with the 30 tee. And that would be where the system would split.

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[Dbluff]

No, because you'd have to route both brake lines into a single line if you only have one airpack. The air system and tanks are just to supply air to the airpacks.


Edit:
Here's a diagram from the brake line side of things and how the normal system works. 21-23 is the line out of the single circuit MC. That feeds into the airpack shown below. The output of the brake fluid is from 22-23 which feeds out to the tee 30 that then feeds the front and rear axles. You'd need a second air pack to plumb up things to keep a dual circuit MC dual. You'd do away with the 30 tee. And that would be where the system would split.

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Great diagram.
Hmmmm, not a hydraulic or brake expert.

But at that 30 tee, could there not be a splitter valve or some sort of that would close either side in an event of a brake cylinder fail? That seems the cheapest and easiest route. If there is such a thing out there it would allow then safety to both sides of the brake system.

i see on google a proportional safety valve can do the deed, maybe…

“The safety switch built into this brake line valve senses when your brake system is producing unequal or lower pressure to one or more of the wheels, usually caused by a component failure. When the valve senses this drop or change in pressure it will cut off the pressure to the port supplying fluid to the defective brakes, thus stopping the leak.”

Front Disc Brake and Rear Drum Brake Line Valve

Upgrade your brake system with LEED Brakes' Front Disc Brake and Rear Drum Brake Line Valve for improved safety and reliability.. This chrome proportioning valve is designed for high-grade performance.

leedbrakes.com

 

[patracy]

Those valves still need two inputs for the two outputs.

 

[Dbluff]

In theory an in-line single proportional or safety valve on each side of the tee 30 to isolate front and rear brakes, I would suspect could add a good safety benefit if pressure is lost, would allow at least to stop as it should close the valve under a pressure drop scenario.

but, we have kind of derailed the OPs owner a little.

Im curious on his find of that bus/Rv MC too.

 

[HDN]

I just discovered this thread thanks to @patracy linking it from his brake line failure thread. I think this is all really neat going into modern safety solutions for brake redundancy on the old trucks!

Having read through the entire thread, there's one thing I'm not entirely clear about: Can a split-circuit brake system be installed using only a single air booster? The most recent posts suggest that dual-circuit master cylinders still need dual boosters like what were installed on the later USAF deuces and the M35A3. Maybe I'm getting a little confused because it seems that the system that @fleetmech suggested uses air at the pedal to power-actuate a dual-circuit master cylinder, whereas the system that @patracy and @Dbluff are talking about uses a hydraulic master cylinder at the pedal to actuate an air booster which provides power-assisted braking to the wheels.

Am I understanding this correctly?

 

[patracy]

I've explained it in post #83. You have to have two air packs.

What fleetmech mentioned and jeepsinker is using a air actuated MC from a trailer to split the brake system. My concern is that if you lose the main MC, you've lost your trailer brake MC. Because no fluid pressure into the airpack means no air out of the air pack. And you're back to no brakes again with no gain.

 

[HDN]

I've explained it in post #83. You have to have two air packs.

What fleetmech mentioned and jeepsinker is using a air actuated MC from a trailer to split the brake system. My concern is that if you lose the main MC, you've lost your trailer brake MC. Because no fluid pressure into the airpack means no air out of the air pack. And you're back to no brakes again with no gain.

I understand now, thanks! And I also understand now why an emergency spring brake failsafe was discussed. The problem with that failsafe is that without somehow splitting the front hydraulic brakes from the rest of that part of the system, all the brakes would be slammed on air loss, creating a major control issue due to front wheel lock-up. Now we're back to splitting the air system like the stock dual-circuit setup

To make this really work safely, the brake pedal would have to be set up like a vacuum brake pedal on a car, with the MC piston in-line with both the MC and the booster so that if the booster fails, the pedal would still directly work the hydraulics. I don't know if that kind of air-hydraulic pedal-MC setup exists - haven't looked it up yet.

The Hydro-Max booster you mentioned does that, but needs a hydraulic pump of some kind to work. I suppose you could use an electric pump to make it work instead of installing a belt-driven hydraulic pump if one wasn't going to install hydraulic power steering. Even if the electric pump quit working you'd still have unassisted brakes left.

Hmmm, the M39 and M809 5-tons have a hydraulic power steering pump. How hard would it be to install a Hydro-Max booster in one of those to get split-circuit brakes?

 

[patracy]

I'm going to be adding power steering to my truck. So I'll be installing a LDS PS pump. But one could also build a bracket and hang a GM style PS pump too if you needed.

I plan to mount my MC/Hydro-max booster to the firewall. I'm going to use pillow blocks to hang a 1" shaft from the firewall to allow the pedal to be mounted from and a lever to work the MC. It will also allow me to link in a treadle valve too for the trailer brakes.

 

[HDN]

To make this really work safely, the brake pedal would have to be set up like a vacuum brake pedal on a car, with the MC piston in-line with both the MC and the booster so that if the booster fails, the pedal would still directly work the hydraulics. I don't know if that kind of air-hydraulic pedal-MC setup exists - haven't looked it up yet.

I did a little bit of research this morning about this type of air-boosted MC. It doesn't seem to exist after all

If I ever bought an old deuce with single-circuit brakes, I'd consider going with a separate electric pump that does either vacuum or hydraulics for brake boosting. The important thing is that the booster is in line with the master cylinder plunger so that the brake pedal will still work the wheel-side of the brakes even if the boosting system fails. That is how the Hydro-Max and modern vacuum-boosted systems are set up.

For hydraulic setups without power steering, I'd get an electric power steering pump to supply booster pressure.

 

[banditt1979]

@patracy have you looked for any of the master cylinder adapter fittings? Only one I could find so far that fits is the 1/2-20 straight to 1/2-20 inverted flare adapter for the front port. Edelmann #265500. Having no luck finding a fitting for the 9/16-18 rear port.

 

[patracy]

I'm going to just use the right size fittings on the new lines. No adapters.

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[banditt1979]

I'm going to just use the right size fittings on the new lines. No adapters.

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Yes I am too. Problem is, the master cylinder I received does not have a flare insert. Therefore, I need brass adapters to connect the brake lines to the master cylinder. You may want to check yours to make sure it has the flare inserts.

 

[patracy]

Yes, we have the same MC save for the resv. Use a bubble flare there instead of a inverted flare.

 

[fleetmech]

I've explained it in post #83. You have to have two air packs.

What fleetmech mentioned and jeepsinker is using a air actuated MC from a trailer to split the brake system. My concern is that if you lose the main MC, you've lost your trailer brake MC. Because no fluid pressure into the airpack means no air out of the air pack. And you're back to no brakes again with no gain.

The system I described would not suffer from those issues, nor does it use an airpak at all. The only deuce hydraulic brake components retained would be the wheel cylinders.

Pressurized air from the tanks, modulated by a standard big rig treadle valve would be sent to one or more big rig brake chambers, which operate one or more fluid masters, which send fluid directly to the wheel ends. The exact quantity of air can/ masters could be tailored to suit the needs and concerns of the driver.

If you want redundancy above all else, you could use three air cans and three single circuit masters, one for each axle. the rear two would be operated by spring brake chambers for loss-of-air situations, the front would be a standard front air can to avoid a front axle skid.

The foot brake/ treadle valve would also modulate air to the trailer brakes (just like a tractor trailer) so they would be unaffected by the trucks hydraulic system.

 

[banditt1979]

Yes, we have the same MC save for the resv. Use a bubble flare there instead of a inverted flare.

View attachment 881350

Do you know of a 9/16-18 tube nut that accommodates a 5/16" OD tube bubble flare? All I'm seeing is 3/16" tube when searching.

 

[HDN]

The system I described would not suffer from those issues, nor does it use an airpak at all. The only deuce hydraulic brake components retained would be the wheel cylinders.

Pressurized air from the tanks, modulated by a standard big rig treadle valve would be sent to one or more big rig brake chambers, which operate one or more fluid masters, which send fluid directly to the wheel ends. The exact quantity of air can/ masters could be tailored to suit the needs and concerns of the driver.

Is there something in this setup that would keep the steering axle brakes from locking up if air is lost? Perhaps a diagram would help illustrate this.

 

[rustystud]

The system I described would not suffer from those issues, nor does it use an airpak at all. The only deuce hydraulic brake components retained would be the wheel cylinders.

Pressurized air from the tanks, modulated by a standard big rig treadle valve would be sent to one or more big rig brake chambers, which operate one or more fluid masters, which send fluid directly to the wheel ends. The exact quantity of air can/ masters could be tailored to suit the needs and concerns of the driver.

If you want redundancy above all else, you could use three air cans and three single circuit masters, one for each axle. the rear two would be operated by spring brake chambers for loss-of-air situations, the front would be a standard front air can to avoid a front axle skid.

The foot brake/ treadle valve would also modulate air to the trailer brakes (just like a tractor trailer) so they would be unaffected by the trucks hydraulic system.

One thing you should know about brake cans is the diaphragms need to be replaced every six months to a year.
They also can just tear out of the blue. I personally would not trust my life to just two brake diaphragms.

 

[fleetmech]

One thing you should know about brake cans is the diaphragms need to be replaced every six months to a year.
They also can just tear out of the blue. I personally would not trust my life to just two brake diaphragms.

No, they absolutely do not "need to replaced every year". Thats ridiculous. My fleet has sent trucks to the scrap yard with their original cans still on them.

As for the loss of air lockup, I have described possible ways to avoid it in all of my recent posts, though frankly Im not concerned about it. When you get right down to it, Id rather the failure mode be full brakes, than none. And that would only happen in case of a catastrophic loss of system air pressure, which is exactly when you would want it to go into failsafe mode...