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

[Unforgiven]

Pressure in the front circuit will always equal the pressure in the rear circuit, even though the volumes are different.

I must respectfully disagree with this. What you said is only true for a single circuit system because of Pascal's principle. It is also mostly true for 4 tire vehicles. And it also assumes the shoes are already tightly touching the drums (full lockup position). In that case I agree with you.

As far as I understand the brakes on this truck, all the wheel cylinders are identical, as are the shoes. Therefore, the cross sectional area of each wheel cylinder piston is identical. To obtain the same X throw of the wheel pistons, they must each receive the same volume of fluid. V=A*X

Having the same pressure at say full lockup for front and rear wheels means twice as much fluid went rear compared to front. Therein lies the dilemma with the 4 tire master cylinder. A single bore master cylinder with equal sized outputs will send equal volumes to each circuit. That will lock up the fronts & leave the rears free. You'll skid the fronts up to every stoplight. Most probably you will blow the front plunger in the master cylinder trying to stop.

Now, the friction associated with it will vary depending on what % of the truck's weight is over that particular wheel is a good point. But as someone already pointed out, with drum brakes you are supposed to adjust them all the same.

My guess is the volume problem is why the spicergear guy opted to put them back into one circuit.

 

[mudguppy]

Disc brakes?

clue me in

F550 brake booster, MC, calipers, and F700 rotors.

 

[mudguppy]

... In OEM as produced trim on modern equipment, it delivers equal pressure to equal brake apparatus on each wheel, just as it should. ...

so you believe there is no proportioning in a modern brake system? then could you illuminate me as to why the front rotors on F350/450/550 are larger than the respective rear rotors (because this is mechanical proportioning)?

 

[Jake0147]

I must respectfully disagree with this. What you said is only true for a single circuit system because of Pascal's principle. It is also mostly true for 4 tire vehicles. And it also assumes the shoes are already tightly touching the drums (full lockup position). In that case I agree with you.

As far as I understand the brakes on this truck, all the wheel cylinders are identical, as are the shoes. Therefore, the cross sectional area of each wheel cylinder piston is identical. To obtain the same X throw of the wheel pistons, they must each receive the same volume of fluid. V=A*X

Having the same pressure at say full lockup for front and rear wheels means twice as much fluid went rear compared to front. Therein lies the dilemma with the 4 tire master cylinder. A single bore master cylinder with equal sized outputs will send equal volumes to each circuit. That will lock up the fronts & leave the rears free. You'll skid the fronts up to every stoplight. Most probably you will blow the front plunger in the master cylinder trying to stop.

You would be correct IF you took the master cylinder apart and welded all the parts together.
A dual outlet cylinder does not work like this. Volume is variable by design between the front or rear circuit. it does not matter if one circuit takes more. Neither builds pressure until both meet their volume demand (or reach the travel limit in the case of a blown line).

Here is a very good animation of how this works (Click the red arrow)
HowStuffWorks "How Master Cylinders and Combination Valves Work"

Now, the friction associated with it will vary depending on what % of the truck's weight is over that particular wheel is a good point. But as someone already pointed out, with drum brakes you are supposed to adjust them all the same.

The friction won't vary at all with the weight, only the available traction. Yes they should all be adjusted the same, but again, the fluid volume available is variable.

My guess is the volume problem is why the spicergear guy opted to put them back into one circuit.

Only he can answer that one. I wasn't there.

 

[mudguppy]

... Volume is variable by design between the front or rear circuit. it does not matter if one circuit takes more. Neither builds pressure until both meet their volume demand (or reach the travel limit in the case of a blown line). ....

this was my understanding and the basis of my statement when i said "this discussion needs to move from 'volume' to 'pressure'."

i believe the front brakes have the ability to [and should!] play more of a role in the braking effort.



therefore,

1. if the front brake components are identical to rear components, i believe the front should recieve a higher % of pressure in the rear, whether it be by proportioning or other
2. OR, the front components should be larger or of higher capacity than the rears to take more share of the total braking effort; this is inline with the fact that most modern brake systems have sized the front components larger than rear components.

so, again, i believe a brake system should be biased towards the front circuit (whether by pressure or by mechanical advantage) and that a circuit that does not proportion is actually a dis-proportional system!!!

 

[Jake0147]

so you believe there is no proportioning in a modern brake system? then could you illuminate me as to why the front rotors on F350/450/550 are larger than the respective rear rotors (because this is mechanical proportioning)?

First, let me clarify that I was refering specifically to the HydroMaxx in that statement. I was not suggesting that the Super Duty brakes were appropriate or recommendable on something this size.

But, that is indeed exactly how the Hydromax are set up. On a given chassis you will find that the brakes are the exact same size at all points.

The Super duties are not in the same class here, but yes there is a slight bias built into them. A straight bored dual outlet master, straight plumbing to the axles (barring an anti-lock event), and the same caliper at all four corners. The rotors are approximately one inch different in all applications that I know of. That is a bias, you are right. But you are comparing a broad range of trucks with a GVW from 8800 to 19,500 pounds to a truck with (when transferrred to the same scale) a 40,000 pound truck. As I said however, this is already done for you. The deuce is already biased to zero bias with the single outlet master, or with the dual outlet master configured to any combination of axles and wheels that you see fit, so long as you don't get into stepped bore masters, the bias remains as it should be.
FWIW, a 250 superduty takes a larger rotor on the front. I'll have to take your word on the 350, but evert 450 and 550 we have at work takes the big rotor in the back.

 

[Jake0147]

You posted while I was posting...
I do not agree that the fronts automatically should recieve more pressure. Ford decided somewhere near the 350 must be the point where the rear brakes should start to recieve more "effectiveness" than the front brakes.
International, Freightliner, Chevy, and Ford all wend with equally sized and applied brakes on medium chassis vehicles all the way through 26000 pounds. If you can get your hands on one, have a look at comparable (CDL beaters) in that class with air brakes. The diameter of the drums and the diameter of the cans. You'll see that in air brake applications for the same truck they apply much more brake to the rear axle, in some applications literally two times as much stopping force at any given pedal application. Larger trucks stepping into the tandem axles use these same larger brakes at all wheels, thus leaving very very little front wheel braking relatively speaking.
Therein lies the Deuce's engineered in proportioning. Equal pressure to all brakes leaves you with a very similar and appropriate amount of front/rear bias in your braking that is very much in accord with modern standards.

I'm not sure wht you mean with a 'disproportioned' brake system. No proportioning valve is the penultimate precision proportioning valve. Always exactly equal, without fail and without error. Which would be very faulty if a proportioning valve were called for, but they are really very seldom used anymore.

 

[mudguppy]

Jake, you're right about the rear discs: 450 and up are larger in the rear (14.5" f, 15.5" r) and 350 and down are smaller. and to think i was just researching those parts...

yeah, i see what you're saying: the axles w/ the large amount of weight are recieving more braking capacity. i got lost because i am viewing the deuce as a primarily empty truck, where the fronts will be seeing more weight than the rears respective to braking ability. if it were my deuce, then just like 99% of every other deuce owner on this forum it'd be 99% empty 99% of the time.

though, i don't really see the correlation between the deuce and a full air-braked modern tadem truck - they just don't seem like apples/apples, whether it be the actual system, load class, whatever. and i understand that modern systems apply more air to rears because that's where the load or bigger drums are - the deuce doesn't do this. so is the deuce at a conveniently magical point that it is perfectly balanced and needs no proportioning?

the angle i'm coming from is my bob'r - it is a tall 4x4 and will not be a load hauling truck. therefore, i will be building a mechanical advantage into the front braking circuit by using a larger front disc than rear (15.5"/14").

 

[Unforgiven]

Here is a very good animation of how this works (Click the red arrow)
HowStuffWorks "How Master Cylinders and Combination Valves Work"

Good link. So what this means is the rears, even with 4 tires, will expand to have shoes touch the drums & at the same time the fronts will expand matching the pressure. Is that correct?

So at full lockup all six will have the same force. I hope I am understanding this right.

Then why didn't the Hydromax guy run dual circuits?

 

[Seatyger]

Not wanting to sound too Mechanically challenged........... can a system as being described here be applied to an M135 with the original power train?

Thanks.

Jim

 

[Jake0147]

Then why didn't the Hydromax guy run dual circuits?

I can't answer that except to point out a couple fof things that he mentioned in this post.

He was frustrated with the air on his truck, and decided it needed to go. He didn't need "better" brakes, he needed "different" brakes. Ones that would operate without the air system in place.
He already had hydraulic power available, but did not vacuum, which narrowed his choices.
He tried Hydroboost but it wasn't enough. (very similar to HydroMax but lighter duty. It'll be in the CUCV TMs) My guess is that even if he had tried to "split" the hydroboost, I don't think there's one big enough to do four brakes out of one chamber, so that one might have needed to be "joined" so that 100 percent of the possible fluid volume could be delivered.
He then tried this "heavy duty" version of what he had.

So my guess... Looking for just "brakes" and not so much "upgraded brakes" I think that the new dual outlet system was probably just joined at a "T" fitting to feed the existing single circuit lines that were in place. He did specifically say that it was to "simplify" the installation.

But again, that's only what I can get from this post. This post is the extent of my knowledge on his specific installation.

 

[Unforgiven]

My guess is that even if he had tried to "split" the hydroboost, I don't think there's one big enough to do four brakes out of one chamber

Now where have I heard that before?

I'm definitely going to do the Hydromax upgrade before summer. If I can't find an appropriate master cylinder, for say a dual axle motor home, Then I'll try my goofy 3x3 dual circuit. And if that doesn't work I'll put it back into one circuit like the spicergear guy did.

While working, there should be no difference between a single circuit and a 3x3 dual circuit. It's only in the unlikely event of a problem that the asymmetry would surface. But I repeat, I'll take 50% asymmetrical braking above 0% symmetrical braking in an emergency. I'm also planning power steering by summer which means fighting any brake asymmetry in an emergency is feasible.

Thanks for the mc animation. A picture is worth a thousand words.

 

[Jake0147]

Now where have I heard that before?

I said this about a Hydro boost system, not Hydromax.. Both hydraulically assisted hydraulic systems, but one in the 10K ish gvw range, the other in the 26K gvw range, and much, much higher if you go back a few years (with wrecking yard parts). We're talking about bicycle brakes bolted onto a Harley Davidson here...

While working, there should be no difference between a single circuit and a 3x3 dual circuit. It's only in the unlikely event of a problem that the asymmetry would surface.

This I will definitely agree with. The axle that is split will not care which circuit the pressure comes from, so long as the pressures are equal. And as much as I am hashing this whole thing out, I am not disagreeing in any way that any available braking after a catastrophic component failure is better than none at all.

But I repeat, I'll take 50% asymmetrical braking above 0% symmetrical braking in an emergency.

This is the part that I'm having a really hard time with... You say this as if there are only two options. I don't see what is wrong with wrong with 50 percent symmetrical braking?


I also have some additional food for thought on the proportioning issue. And this is FOOD FOR THOUGHT, as this stretches beyond my daily experience with the above braking systems... It will also obviously be for a 6X6 configuration only...

Anyway, there WAS a dual outlet master cylinder installed to the late model air force deuces, and it was also used on the A3 ESP program, so what did they do? Turns out, the answer is not so clear. In the NOMENCLATURE (the name assigned to the part) there is discrepancy depending on where you look the part up. But there is a "valve" between the two outlet lines. Somp places it's listed as a differential valve, and some as a differential and proportioning valve... So, what is it really?

On the old site in the TM section, third page, second from the top is SMARPI 9-2320-209-14&P which is the supplemental manual for A2 varieties with the split brake system. On page F13 of the document (page 66 of the PDF) there is a picture of the master cylinder and illustration number 8 shows the valve.

This valve IS a differential valve, because it does run the light on the dash... In that manual it is called a "differential valve", but as I said, other places (including the 386 TM for the A3) list it as a "differential and proportioning valve". So what is it? I don't have one, however looking at this picture (or the picture in the 386 TM shows several drawings of the part. The pressure differential valve (and the associated switch) is clearly there, but I see no other valving. I also see diagnostic steps to diagnose a failed differential valve, but none to diagnose a failed proportioning valve. (which even in the same "block" will remain separate valves with separate functions). The "proportioning" part which acts on a single line is clearly missing from the TM. There is no law saying that they all look exactly alike, but here's another Howstuffworks illustration showing what I mean and identifying aproximately what a proportioning valve (or proportioning section of a combination valve) would look like.
It could be somehwhat different, but somewhere on that block there has to be a place with another valve screwed into it plumbed (internally) so as to act on one line but not the other.

HowStuffWorks "How Master Cylinders and Combination Valves Work"

If someone had a real live one it'd be a lot more conclusive, as to what a much more "modern" engineering standard has deemed appropriate as far as biasing the brakes. Based on what I've listed, I'm leaning toward it being an unbiased system, however it may be that this is not the case. FWIW, they did split the brake with the front axle as one circuit and the rear axle as a second circuit, but they had two airpacks to do it, each with a full 100 percent system capacity, so either is easily capable of running all six brakes at once. Again, no "real" conclusion there either...

Anyhow, as you can probably tell I am very intrigued with the idea of retrofitting this system. (I dunno why, I have lots bigger fish to fry right now...) and when the time comes that you do this, I would love to know the outcome, as well as installation photos. As I said earlier, it's not the performance, but the mounting requirements (and my requirements not to alter the pedals and the appearance of the trucck) that have prevented me from doing this thus far.

 

[Unforgiven]

There is another, more expensive option. Electric driveline retarders would be the ultimate failsafe, redundant brake system. But at $6K + it would be worth more than the whole truck!

 

[Unforgiven]

Would you happen to know the exact diameter & throw of the stock master cylinder?

 

[jesusgatos]

There is another, more expensive option. Electric driveline retarders would be the ultimate failsafe, redundant brake system. But at $6K + it would be worth more than the whole truck!

I would like to hear more about this. Do they generate electricity? Oh boy, oh boy. If they do, I'm SO interested. I would love to be able to add regenerative braking to my M109 motorhome conversion. Maybe start another thread and post a link, or send me a PM? Thanks!

 

[Unforgiven]

Google "Klam driveline retarder" or "Telma driveline retarder" They do not generate useful electricity. They use EM eddy currents to dissipate vehicle Kinetic Energy as heat.

 

[tm america]

i think the stock dual brake system has it right since it not only gives you dual brake system it also doubles the available volume with the dual air packshydro boost brakes are great as long as the truck is running and everything is working but when its not it gives to the worst ratio for stopping.due to the fact the master uses a bigger diameter piston than with anyother system.i also like having power brakes to stop with even after the engine cut out and you loose that with hydro boost

 

[Unforgiven]

BTW,

Somebody wanted to know what a triple master cylinder looks like attached to the pedal:

http://www.summitracing.com/parts/TIL-72-605?autofilter=1∂=TIL-72-605

 

[tm america]

some vehicles with hybrid and cvt trans use regenerative systems but are to small to be usefull on a deuce.it's built into the trans not the brakes