Dual Circuit Brake Engineering Thread

[tobyS]

Thanks Peashooter. Do you know if there are actual schematic drawings of the brake and air system, not just assembly drawings?

 

[jkcondrey]

PEASHOOTER, Both my airpacks are the short style. I know that all my fluid lines are correct, that's simple enough. Its just odd that I would have air only gushing from the vent line, no fluid just air like a leaking air hose. Are there any differences in the air port locations on the airpacks? I am just thinking that maybe the one being used for the "vent" is actually the gladhand port, if it were being used. The same port, on the driver side airpack on mine runs to the gladhands, which is why I plugged the port of the passenger side pack. Ill dig through the tms again and try to find some definitive answer, but it looks like I may just try to reverse the vent and the plugged port and see what happens.

 

[peashooter]

PEASHOOTER, Both my airpacks are the short style. I know that all my fluid lines are correct, that's simple enough. Its just odd that I would have air only gushing from the vent line, no fluid just air like a leaking air hose. Are there any differences in the air port locations on the airpacks? I am just thinking that maybe the one being used for the "vent" is actually the gladhand port, if it were being used. The same port, on the driver side airpack on mine runs to the gladhands, which is why I plugged the port of the passenger side pack. Ill dig through the tms again and try to find some definitive answer, but it looks like I may just try to reverse the vent and the plugged port and see what happens.
View attachment 755172

You probably know this from the TM diagrams, but the dual circuit trucks have a priority valve on the drivers side frame rail (Bendix 278614 DC4). Both airpacks have an air line going to the priority valve and from it a single airline goes to the gladhand.

Check out these, maybe it will help. I looked under my truck but its cold, and the skid plates covering the airpacks block the view of the air lines and where they run to.
https://www.steelsoldiers.com/showt...-with-Photos&p=1409240&viewfull=1#post1409240

I really dont know if there is a nice layout of the air lines. If you look at this TM, it gives part numbers for the Air lines and at the end of the TM, it shows dimensions of the airlines and what they are for (for example 5934109 is figure G-6 "TUBE ASSY, VENT, RIGHT HAND AIR HYRDAULIC UNIT TO TEE").
https://www.steelsoldiers.com/attachment.php?attachmentid=339700&d=1339731822

 

[jkcondrey]

You probably know this from the TM diagrams, but the dual circuit trucks have a priority valve on the drivers side frame rail (Bendix 278614 DC4).

Hmmm. The priority valve is definitely missing. I missed that part for the swap. I believe you are right that the vent line is in the correct spot after i layed under the truck for 20 minutes staring at both airpacks. To give a better idea of what I have done: pedal bracket installed, dual master installed with the remote reservoir up on firewall. Added a third air tank to supplement the standard 2 on the a2. I added a "t" to the second tank and ran a line to the third tank, with its exit line running straight up to the new passenger side airpack. I left the original tank line running up to the driver side original airpack. Added the vent line on the new passenger airpack and ran it up to the old vent t above differential on frame.

I was thinking that this would suffice for getting air pressure to the new airpack and still maintaining the original airpack pressure and gladhand. I believe you are right about the vent line being plumbed correctly. So, if I'm understanding this correctly, I need to add the bendix priority valve to balance the air out?? I did print off the a3 tm diagram you loaded up to use as a guide, but with it only having the two tanks with a split tank, it doesn't match up correctly. I need to figure out where the valve should go in relation to the plumbing i have now or reroute it to use the valve. I hope this is whats needed as i really do not want to rebuild both airpacks.

 

[peashooter]

Honestly I’m not sure if the priority valve will solve your current issue, in fact I suspect it won’t, but figured I’d mention it anyway. I’d recommend pm’ing someone like gringeltaube or rustystud.

 

[rustystud]

PEASHOOTER, Both my airpacks are the short style. I know that all my fluid lines are correct, that's simple enough. Its just odd that I would have air only gushing from the vent line, no fluid just air like a leaking air hose. Are there any differences in the air port locations on the airpacks? I am just thinking that maybe the one being used for the "vent" is actually the gladhand port, if it were being used. The same port, on the driver side airpack on mine runs to the gladhands, which is why I plugged the port of the passenger side pack. Ill dig through the tms again and try to find some definitive answer, but it looks like I may just try to reverse the vent and the plugged port and see what happens.
View attachment 755172

You have your lines mixed up. Use this diagram. It is for the "long style" but the fitting locations are the same.
I also decided to post this picture of the "short style" showing the correct way to connect the lines.

View attachment Scan0159.pdfView attachment Scan0160.pdf

 

[jkcondrey]

There we go. Thanks Rustystud. Where is that diagram of the airpack at? I have yet to see that in any tm I sourced. Ill get to swapping those up. Thank you and peashooter too.

 

[jkcondrey]

Success!! Split brakes, great pressure, no leaks! I can go scare the neighbors now!

 

[rustystud]

View attachment 755268Success!! Split brakes, great pressure, no leaks! I can go scare the neighbors now!

Glad to hear it ! The TM is a rare one I own. It has all the "air" components for the deuce like the air compressors and relays and air-pacs.
I posted the rebuild information for the air-pacs here at Steel soldiers. It is in the TM section.

 

[41cl8m5]

I've been following this topic for some time now and there is a lot of good information. I started a thread titled "M35a3 schematics" after searching and not finding any. I found what I was looking for in the TM. Should have started there, kicking myself on that one! Anyway, I put copies of the different schematics that are in the TM on that thread; wiring, air, brakes....

Unfortunately, I have not figured out how to do a link from my old out of date iPad on this site or I would have done it

 

[tobyS]

Now I have to work on making a legible print. I guess I had located these in the TM some time back...memory lapse. Had problem with size then also. Here is a link to the other thread where you posted them. Thanks

https://www.steelsoldiers.com/showthread.php?184894-M35a3-schematics

Also a link to the TM

https://www.steelsoldiers.com/upload/M35/TM9-2320-386-24-1-2.pdf

Go to the back pages 750-754

 

[7bdiver]

I was thinking about how to cheaply reduce the risk of individual failed brakes at each wheel.

What i came up with is a kind of check valve that would in a sense limit the volume of fluid you could hemorage on each line. It would be based on the amount of fluid that can be used by a brake cylinder as the limiting factor.

Basically, it would be an in-line reservoir that would deplete and close if more than the normal amount of fluid is pulled through.

Would still need to build in a bypass of sorts to bleed the brakes, but here is a lil drawing of the idea. Its very basic.

The internal plunger will aplly pressure on the fluid downline till it runs out, then seals that wheel off. I would put them as high up the system as possible. Could even make it a multi piston single unit with one inlet and six outlets. This would protect against blown lines, and leaks.

 

[7bdiver]

Offhand, does anyone know the volume of fluid that these brake cylinders use on a stroke?

I could machine a six piston in line unit pretty easy.

I'll CAD the idea up and post it. See what you guys think.

 

[Robo McDuff]

I was thinking about how to cheaply reduce the risk of individual failed brakes at each wheel.

What i came up with is a kind of check valve that would in a sense limit the volume of fluid you could hemorage on each line. It would be based on the amount of fluid that can be used by a brake cylinder as the limiting factor.

Basically, it would be an in-line reservoir that would deplete and close if more than the normal amount of fluid is pulled through.

Would still need to build in a bypass of sorts to bleed the brakes, but here is a lil drawing of the idea. Its very basic.

The internal plunger will aplly pressure on the fluid downline till it runs out, then seals that wheel off. I would put them as high up the system as possible. Could even make it a multi piston single unit with one inlet and six outlets. This would protect against blown lines, and leaks.

I think we discussed something similar with Ron (73M819) 5 or more years ago; airplanes use valves for explosive pressure loss. No time to find the post now, there was a reason it would not work on a 5-ton, not sure what it was.

If I understand correctly, what you are suggesting is a bit different. Have to look at it in the morning, when I am not overtired.

 

[Another Ahab]

I was thinking about how to cheaply reduce the risk of individual failed brakes at each wheel.

What i came up with is a kind of check valve that would in a sense limit the volume of fluid you could hemorage on each line. It would be based on the amount of fluid that can be used by a brake cylinder as the limiting factor.

If this proves practical and effective maybe you should consider investing a few grand toward filing a patent.

Who knows?!

 

[Mullaney]

If this proves practical and effective maybe you should consider investing a few grand toward filing a patent.

Who knows?!

.
If I remember correctly, the "79ish" Chevrolet pickup trucks have (had?) a proportioning valve in the brake system just below the master cylinder. There is a "rubber button" on the front of it and if the front or rear brake lines exploded, the functional part of the brake system would still be operational.

It's fuzzy, but I remember learning that the hard way repairing a truck. Easily found the busted rubber line, but I couldn't figure out how to bleed the brakes. Fluid wouldn't pass to the back axle. Problem was solved when one of the older guys pointed out the "button" on that valve - and PRESTO - fluid flowed again...

 

[7bdiver]

I'll have to look into what you were saying the chevy's used. They may already have an easier solution.

Here is the idea for a front back split system.
If on fails, the reservoir piston will bottom out and shut that line off. The bottom volume would be for the rear, larger since it has twice the cylinders to feed.

Single inlet from the master with a bleeder, and a split output to the front / rear brakes. And their respective bleeders.

Basic mockup. Does it make sense or feel like a doable system?

 

[Mullaney]

I'll have to look into what you were saying the chevy's used. They may already have an easier solution.

Here is the idea for a front back split system.
If on fails, the reservoir piston will bottom out and shut that line off. The bottom volume would be for the rear, larger since it has twice the cylinders to feed.

Single inlet from the master with a bleeder, and a split output to the front / rear brakes. And their respective bleeders.

Basic mockup. Does it make sense or feel like a doable system?

.
That seems like a good way to save your bacon if there was a "fluid failure" at the front or back of the truck. It would give you the ability to stop rather than losing all braking for sure!

 

[Robo McDuff]

OK, I'm awake now (remember, I am across the pond from you people).

It actually was my own thread on how to split a brake circuit on a 5-ton. Ron (73M819) actually came up with the hydraulic fuse idea (post 15).

Such fuses are standard issue for all types of aircraft:
Hydraulic fuse or velocity fuse for aircraft

My post 24 in that thread shows links to all kind of hydraulic fuses. I am not sure, but somehow I have in my memory that it either was too complicated-expensive to do for the whole truck, or would not work for whatever reason.

We never continued, since restoring my truck once it was in the Czech Republic got into a dead end. Then with Ron passing away and some health and financial problems here even the discussion died out.


There is an other interesting thread on a split brake system in a deuce, also rather old but still valid.

Forklifts, knuckle cranes and similar use such fuses. One fuse costs about $100, you would need at least two or three. However, for those applications, the normal flow is slow, and easy to separate from high velocity loss.

Performing an emergency braking, the pressure change of braking is more abrupt and stronger also, so not sure if that would not influence the velocity fuse.

 

[Another Ahab]

Problem was solved when one of the older guys pointed out the "button" on that valve - and PRESTO - fluid flowed again...

Lookey there:

- Older Guys might sometimes seem like a PIA, but

- Every now and then, they're real useful!

(Full Disclosure: I am myself an O.G.)