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m35 brakes

rustystud

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Deuce brakes are "intresting", being basically a 1930s design. Because they use a single wheel cylinder and duel fixed anchor pins there is only one leading shoe, and one trailing shoe for each drum, and the shoes switch depending on vehicle direction when the brakes are applied.
When you are going forward and apply the brakes, the forward shoe becomes the leading shoe, when you are in reverse, the rear shoe becomes the leading shoe, this also means that the brakes work equally well, (or bad), in either direction.
But in reality, you don't often have to make hard/fast stops from high speed in reverse, and so the Deuce design, while strong and simple is lacking in stopping power by modern standards.
In most any type of drum brake, the leading shoe does most of the work. With the fixed anchor pin design, you effectivly give-up ~25>30% of your braking power,, but with enough power assist rhe system works.
The modern system, (Kelsey-Hayes/Bendix)whereby the shoes are connected together by a "floating" anchor allows both of the shoes to "cam" themselves into the drum, resulting in a large increase in stopping power for the same brake-line hydraulic pressure.
The "floating anchor" system was originally designed for aircraft, which, (as planes got bigger/heavier/faster landing speeds), needed brakes that would "stop" without power assist.
Actually there is NO big rig or bus today that uses the system that cars did. They all have anchored brakes. The reason is that the "floating anchor is not strong enough to handle the pressures needed on something like a 8" to 10" wide brake pad.
The modern shoes have actual bushings in the shoes (that must be lubed) due to the forces they must deal with. The only thing the deuce needs is a "S" cam tied to a air-can to make it a modern design.
 

rustystud

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View attachment Scan0059.pdfView attachment Scan0060.pdfView attachment Scan0061.pdf
TM 9-1819B (page 192) states that there is a factor of 17x between the applied air pressure and the resulting hydraulic pressure.
According to TM 9-8651 (1956) the Air-Pak has a "multiple" factor of 10 between the inlet and outlet pressures. What I had stated in my post was that standing hard on the brake pedal I was only able to reach 800psi with no air. With air and applying the brakes normally I was able to get 1600psi .
So to be able to stop normally with full pedal pressure you must have the air system working. Without it you are in deep do-do !
 
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JasonS

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I don't think that is what it says. Read your scanned text again. You multiply the part number by a factor of 10.
 
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SP5

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Actually there is NO big rig or bus today that uses the system that cars did. They all have anchored brakes. The reason is that the "floating anchor is not strong enough to handle the pressures needed on something like a 8" to 10" wide brake pad.
The modern shoes have actual bushings in the shoes (that must be lubed) due to the forces they must deal with. The only thing the deuce needs is a "S" cam tied to a air-can to make it a modern design.
Please, don't mis-interpet my post, I was only trying to point out that the fixed anchor, single cylinder type brakes were, and are strong, but that it is necessary to have some type of power assist in order to develope sufficient braking power in a heavy vehicle.
I used the example of a modern servo type system mainly in order to try to describe the geometry.
Although, the system that uses two wheel cylinders, each with only one piston, and fixed anchors (Duel leading shoe),
developes good effort, but looses effort in reverse.
In no case was I referring to 8>10in wide shoes,, thats a stretch for vehicle thats
only ~24 thousand loaded up.
 

JasonS

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That's what I said didn't I ? I guess I forgot to add the word "multiply" .
You wrote "the Air-Pak has a "multiple" factor of 10 between the inlet and outlet pressures" which is not really what your scanned document states. The document states that you multiply the third part number by 10 to get the hydraulic pressure at an air pressure of 90 psi under full braking. For example for part number A65-11-148, you will get 1480psi hydraulic pressure with 90psi air. There is not a simple multiply by 10 factor.
 
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gimpyrobb

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View attachment 605756View attachment 605757View attachment 605758

According to TM 9-8651 (1956) the Air-Pak has a "multiple" factor of 10 between the inlet and outlet pressures. What I had stated in my post was that standing hard on the brake pedal I was only able to reach 800psi with no air. With air and applying the brakes normally I was able to get 1600psi .
So to be able to stop normally with full pedal pressure you must have the air system working. Without it you are in deep do-do !

Where did that scan come from? Looks like a 5ton air pack to me.
 

rustystud

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You wrote "the Air-Pak has a "multiple" factor of 10 between the inlet and outlet pressures" which is not really what your scanned document states. The document states that you multiply the third part number by 10 to get the hydraulic pressure at an air pressure of 90 psi under full braking. For example for part number A65-11-148, you will get 1480psi hydraulic pressure with 90psi air. There is not a simple multiply by 10 factor.
OK Jason, your just being "obtuse" right now. You know what I meant. I mean I posted the thing and even highlighted it for goodness sake !
 

rustystud

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Where did that scan come from? Looks like a 5ton air pack to me.
Actually it is the first "Bendix" Air-Pak used on the deuce and five tons. Air-Pak is a trademark name from Bendix just like "Posi" is a GM name. This was in the TM 9-8651 . I have an original almost mint condition manual. The only problem was the glue holding the pages together had dried up which made it easier to scan to my computer though.
 

red

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Kinda got what he deserves if you ask me. How long does it take to build full pressure? Maybe 3mins?
Just to clarify, that was in my deuce. Engine had locked up, and all the remaining air in the system had been used already to keep the speed low and controlled.

Care to assume again?
 

rustystud

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I feel like, by the time you need that gage, you're already screwed.
The gauge is just a diagnostic tool. It lets me know of any developing problems. Like if the Air-Pak is malfunctioning or the master cylinder. If my pressure starts to drop I know my air-pak's are not working right, that sort of thing.
 

Another Ahab

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I've been in friend's deuce going down a steep grade about 10-20 mph, with less than 30PSI of air. He was standing on the brakes, pulling up on the steering wheel for more force. I'm surprised the steering wheel didn't break for how much it was bending. The only thing that stopped us was sacrificing the clutch and associated components.


pucker.jpg
 

gimpyrobb

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Just to clarify, that was in my deuce. Engine had locked up, and all the remaining air in the system had been used already to keep the speed low and controlled.

Care to assume again?
Nope. Moving a deuce with no air for the brakes, and nothing to slow it down, you get what you got.
 

rustystud

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View attachment 605865


I like your library, rustytud, and the bonus feature of it is how you can sit and take a rest if you're getting tired climbing the stairs.


:mrgreen:[thumbzup]:mrgreen:
Sometimes I won't even bring them upstairs, I'll just plop down on the steps and start reading. Then later my wife will come looking for me and say "what on earth are you doing out here ? " . I'll of course say "just reading" to which she'll reply " I just don't understand you and that truck ! " . Lately she has started calling my truck "the other woman" .
 
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