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

[tm america]

thats two brake res and one for the clutch hence the two pedals

 

[Unforgiven]

correct.

someone wanted to know if doing dual or even triple MC's was possible. Yes it is, but A good single MC choice is better. Just a "for example" picture.

 

[tm america]

ya you could link the pedals like on a tractor if you wanted problem is the force it take to push three mcs at once

 

[Coldfusion21]

As he mentioned there is an electric motor to power the system in the event of a failure or the engine isn't running. So really this system is more fail safe them a normal brake system that would be very hard to control without vacuum or air pressure.

 

[AN/ARC186]

driveline retarders!

Sounds like me replacing u-joints this weekend!

 

[mudguppy]

... i also like having power brakes to stop with even after the engine cut out and you loose that with hydro boost

no, actually you don't. there is an accumulator in almost all hydro-boost systems to give full braking power if pressure is lost. hydro-max incorporates a seperate electric pump.

also, it's a manual transmission - if you're rolling, then the engine is turning and the pump is making pressure.

 

[Unforgiven]

Okay,

I think I've found the most likely "compatible" master cylinder using the HydroMax boosting system.

It turn out that all of the fairly new Chevy Kodiak & GMC Topkicks up to the C7500 series use the HydroMax. Anything from 2000ish up should have it.

The C8500 used to use air brakes but are now hydraulic but not Hydromax.

I'll bet dollars to doughnuts that the HydroMax system from a C7500 Kodiac, tandem axle truck would fit perfectly (technically speaking-pressure, volume etc.) into the M35. I still need to look into the specs, but right now I'm thinking this is the best option.

 

[Unforgiven]

The Kodiak 7500 tandem axle runs 2000 psi.

The stock M35 runs 1800

I'm thinking a bump stop on the brake pedal limiting it to 1800 psi would be ideal. but for this I'll have to get a psi meter.

The Kodiak runs 4 70mm pistons per wheel up front, disc brakes.

The M35 runs 2 wheel cylinders drum brakes up front. I'll bet anyone here that 4 Kodiak pistons = 2 M35 cylinders, close enough.

I'll do this upgrade in January and let you know the outcome. I plan to install speed bleeders & I'll definitely compare stock to upgrade. There's a great stretch of pavement nearby that's NEVER travelled and at least 5 miles long. I can test there all day without a soul coming by.

Stay tuned in Feb. for my results.

 

[Jake0147]

A couple of quick points-
The HydroMax system (not all hydraulically boosted systems, just the one in question here) uses an electric motor as a backup in case of engine failure. Not "full braking" by any means, but it is there, and while not convenient or comfortable, it is functional for that one last stop, and further to confidently get you to a good place to evaluate further action. You would need a COMPLETE electrical failure, a COMPLETE engine failure (not just loss of power) combined with throwing in the clutch (a dead engine still runs the accessories even if only the wheels are turning it) and you would need TWO complete brake system failures to loose brakes. HydroMax also has a direct linkage, so even if you loose all assist, you still do have some degree of braking, albeit woefully inadequate for regular service, something I would not want to use to get me very far for emergency parking, but it is there, and still beats nothing by a far cry. In other words, there is enough redundancy built into it to easily meet today's new vehicle safety standards.

As for pressures, don't jump the gun here. Pressure is not "on and off", you create the pressure by stepping on the pedal, but you adjust the pressure by how hard you step on the pedal. Modern standards allow for one vehicle to have twice as much pedal effort as another to achieve a maximum stopping force, and you always have and always will have to adjust your pedal effort depending on the load in a vehicle to achieve the same rate of deceleration. HydroMax that is supposed to operate at a maximum of 2000 pounds is (on paper) only capable of generating fifteen hundred or so if the hydraulic pump is worn to the "out of spec but still quite functional without issue" stage. The results (on a disk brake system) is a truck that will still meet it's braking performance criteria, but the pedal that is heavier than normal. How much heavier? You'd have to drive two trucks back to back to be able to pick up on it. Aftermarket brake pads give the same result. I don't think you would ever be able to spot the difference. Even if you did, becuse the pressure is modulated by you, the operator, you'd only notice it after you exceeded the 1800 pounds that your original system is making. (BTW, the 1800 spec is not mine, I have not found or verified this, it comes from this post, just to be clear about what I'm basing this statement on)...

 

[Unforgiven]

Jake,

I can't guarantee flawless results. But here is what I plan to do. I will source out a 6x4 Hydromax. 6 meaning 6 wheels, 4 meaning 4 rear drive wheels (Kodiak doesn't come in 6x6 configuration)

I will then go to my flat, undisturbed patch of asphalt & run a few trials of say 50 to 0 stop times/distances.

Then I will convert over to Hydromax 6x4, assuming I source all the necessary parts by Jan.

Then I will go to the same location & perform several more full stops.

Then I will use the speed bleeds to simulate a front brake failure.

Then I will use the speed bleeds to simulate a rear brake failure.

I will post the results for those who are curious.

I cannot guarantee any success or any failures. All I can say is I will give it the old "college try" and see what happens.

From everything I have read, the stock wheel cylinders are good up to 1800 psi. The Hydromax MC is good up to 2000 psi. Maybe that's important, maybe it's not.

But I would prefer to adjust the brake pedal push to match the max psi, in this case 1800 just in case. I don't want to push more psi than the cylinders can handle.

I will try both powered down, clutch in w/engine running & powered down/w/o engine running clutch in trials.

If it is at least as strong as the stock system then I will call it a success. If it at least stops w/ front or rear then I will consider it an upgrade. If it is worse then I guess I rip it out & stick with the stock configuration.

I apologize to Mother Nature in advance for simulating a front/rear failure using speed bleeders & dumping 2-3 cubic inches of DOT 5 onto the asphalt.. It's all in the name of science.

Hope it helps.

 

[mudguppy]

that sounds like that's going to be a ton of fun!! i, for one, look forward to the results.

 

[Unforgiven]

The hardest part is going to be the brake pedal. I can get the pump, booster & mc w/o too much trouble. The brake pedal, however, will probably require my actually going to a junkyard. Grumble, grumble, grumble. The nearest diesel yard is about 40 miles away and a real dump, no pun intended. I haven't been there since the 1980's & it was miserable then.

 

[jesusgatos]

I'm planning on converting Mah Deuce to a fully hydraulic steering system, and I hadn't decided what to do about upgrading the brakes, but after re-reading this thread I think I'm going to start collecting parts to install a hydro-max system.

I think this system is easily adaptable to these trucks with the exception of the pedal assy. I originally mounted the hydroboost system under the truck nested up beside the transfer case. The Hydro-Max unit had a much larger (wider) reservoir so I firewall mounted it. Room was a little tight but it ended up fitting pretty well. Hood clearance is on the 'just barely' side but it does clear. Although these systems can and are installed with the booster and steering off of the same pump, the several trucks I had looked at with this had seperate pumps for steering and braking.

I'm going to try to do this while retaining the stock pedal assembly. I don't have a cab on my truck right now, so everything is very accessible. No big deal if it doesn't work, but I'm going to try.

Trailering...yes, I have thought about that and if it becomes something that I feel I will definately need, I'll get an air valve from a straight air brake truck and make some linkage to it.

This is something that I'll definitely need to address, and I'm sure there's probably a simple way to do it, but I don't know much about air-brakes or the components used in those systems.

A single way "conversion" like is described in the original post does not gain the redundancy of a dual circuit, even though there are two outlets.

A dual circuit for redundancy IMHO would be worth while if you are choosing to upgrade the brake system anyhow.

As far as mismatched numbers of wheel cylinders on each circuit, there is no discrepancy in the volume of fluid delivered versus required to any circuit (within some reasonable sizing limits, we're not talking about a Kia master cylinder here), a dual outlet master cylinder is self-compensating design. With a constant bore for the front and rear sections of the cylinder, It mechanically delivers a variable volume to each circuit as required to develop equal pressure in each circuit. at all times. The volume is needed to make the pressure, but the pressure is what stops the truck.

You guys are over thinking this...

There is no "proportioning" in this. None needed, none wanted. Equal pressure to all wheels gives "factory" proportioning. That's what you have now, that's what you want. A split master with equal bores front and rear inherently does this. Pressure in the front circuit will always equal the pressure in the rear circuit, even though the volumes are different. Until a failure, then you will have the pedal drop half way, and the mechanical stops will take over and allow the remaining undamaged brake circuit to function normally.

As far as a modern system...
Hydromaxx is a modern system. In OEM as produced trim on modern equipment, it delivers equal pressure to equal brake apparatus on each wheel, just as it should. This isn't a Ford Taurus, all the brakes have to pull their weight. The 70/30 thing that you hear about pretty much stops when you get beyond compact and a few mid sized sedans.
Everything you need for this system is done. All brakes of the same. No metering valve is used. All brakes require the same pressure to operate correctly. No proportioning valve is used. The differential valve if you choose to use it is contained within the master cylinder it's self. There are no other valves to add. If you're doing a disk/drum conversion, if you're adding bigger drum brakes to one axle but not the rest... Then yes you will need some external metering and proportioning, but for stock brakes, it's just a line to the chosen axle.

This is my poijnt. If you're going to do this, it'd be best not to have a failure of course, but if you do...
I would rather come to a complete stop in a straight line with no squeeling, skidding, or other unnecessary drama. That's what modern brake systems deliver, I just can't see why you would go to the extra effort to bypass that feature.

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.

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"



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.



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

Thanks for explaining this to us Jake. I was thinking like Unforgiven, and would have guessed that the rear axles would NOT see equal pressure in a dual-circuit system. Glad to be wrong in this case. More powerful AND safer? Sign me up. I'm glad to hear that I can switch over to dual-circuit brakes.

...i also like having power brakes to stop with even after the engine cut out and you loose that with hydro boost

no, actually you don't. there is an accumulator in almost all hydro-boost systems to give full braking power if pressure is lost. hydro-max incorporates a seperate electric pump.

also, it's a manual transmission - if you're rolling, then the engine is turning and the pump is making pressure.

I share tm america's concerns about the pedal effort required in a hydro-max system with no power, but that's a really good point mudguppy.

Okay,

I think I've found the most likely "compatible" master cylinder using the HydroMax boosting system.

It turn out that all of the fairly new Chevy Kodiak & GMC Topkicks up to the C7500 series use the HydroMax. Anything from 2000ish up should have it.

The C8500 used to use air brakes but are now hydraulic but not Hydromax.

I'll bet dollars to doughnuts that the HydroMax system from a C7500 Kodiac, tandem axle truck would fit perfectly (technically speaking-pressure, volume etc.) into the M35. I still need to look into the specs, but right now I'm thinking this is the best option.

View attachment 158871
View attachment 158872

Thanks for doing all that research, and for sharing what you found out with us.

Jake,

I can't guarantee flawless results. But here is what I plan to do. I will source out a 6x4 Hydromax. 6 meaning 6 wheels, 4 meaning 4 rear drive wheels (Kodiak doesn't come in 6x6 configuration)

I will then go to my flat, undisturbed patch of asphalt & run a few trials of say 50 to 0 stop times/distances.

Then I will convert over to Hydromax 6x4, assuming I source all the necessary parts by Jan.

Then I will go to the same location & perform several more full stops.

Then I will use the speed bleeds to simulate a front brake failure.

Then I will use the speed bleeds to simulate a rear brake failure.

I will post the results for those who are curious.

I cannot guarantee any success or any failures. All I can say is I will give it the old "college try" and see what happens.

From everything I have read, the stock wheel cylinders are good up to 1800 psi. The Hydromax MC is good up to 2000 psi. Maybe that's important, maybe it's not.

But I would prefer to adjust the brake pedal push to match the max psi, in this case 1800 just in case. I don't want to push more psi than the cylinders can handle.

I will try both powered down, clutch in w/engine running & powered down/w/o engine running clutch in trials.

If it is at least as strong as the stock system then I will call it a success. If it at least stops w/ front or rear then I will consider it an upgrade. If it is worse then I guess I rip it out & stick with the stock configuration.

I apologize to Mother Nature in advance for simulating a front/rear failure using speed bleeders & dumping 2-3 cubic inches of DOT 5 onto the asphalt.. It's all in the name of science.

Hope it helps.

Did you ever get into this project?

 

[Unforgiven]

Did you ever get into this project?

I was going to do this, but I've since had a "design change" in what I hope to accomplish with the Deuce.

Originally I was going to put a Kodiak7500 Hydromax system on (from a tandem axle truck) 6x4

But now I have a crazy hair up my back side that I want to research first. I do a lot of off-roading during good-weather camping seasons. And I like to go WAY out into BFE down some medium-challenging trails.

Anyone who off-roads in the Southwest will agree that small berms capable of high centering a Deuce are everywhere. Even what looks like flat terrain can all of a sudden have a wash in the road that is just big enough to scrape the bottom of the frame rails or transfer case.

So I'm mulling over the idea of a liftable pusher axle between the rear tandems & the front. Maybe I will, maybe I won't. But I'm planning on moving the rears back a few feet anyway b/c of an engine swap & crew cab. That will simply make the high-centering concerns worse.

If I decide to put a lift axle on it, then I'll simply use a regular dual-circuit Hydromax master cylinder instead of the 6x4 version. One circuit for the rears, one circuit for the front + lift axle. Fluid volume might be a concern, so I'd have to do more research. Because of this, I decided to do the engine swap & axle repositioning before doing the Hydromax system.

When I get serious about this next year I might find out it is impossible. If so, then I will go back to the original plan of a 6x4 Kodiak Hydromax system.

More importantly, I'm planning to either rebuild or replace all the wheel cylinders & brake shoes this year. That way I'll at least have a freshened up stock system until I decide whether or not to do the Hydromax.

Right now I'm gathering parts & researching. I'm itching to get that Cummins & Allison in the truck. But other things (unrelated to the truck) are keeping me side tracked at the moment.

 

[jesusgatos]

Right on. Thanks for replying. I'm reconfiguring all the storage under my cab right now, hoping to improve the ground clearance and break-over angle. What I can't move, I'll build skid-plates for.

Do you know how that 6x4 Kodiak master cylinder is configured? Just wondering how different (if any) is might be, compared to the regular hydro-max master cylinders. Are the regular hydro-max master cylinders and boosters all the same?

 

[jesusgatos]

Do any of you guys have an extra hydro-max master cylinder/booster setup laying around? Don't even care if it's in usable condition. Right now I'd just like to have something I could use for mock-up, to see if I can make it fit under the cab, using the stock brake pedal. I'm just so deep into so many different aspects of this project, that I can't really afford to go out and buy all these parts right now. But I've got Mah Deuce stripped down to the frame, and this would be the perfect time to tackle this project. If it's possible to make this setup work under the cab, I'm sure I can figure that out. And if it works, I'll be able to give CAD files to someone like streetbikedepot, who could then make mounting brackets for the rest of you fawkers. So, how about it? Anybody?

 

[Unforgiven]

As far as I know the boosters are the same. The master cylinders have different diameter outlets depending on the application. I believe the master cylinder throw is the same in all applications.

I was going to just bite the bullet & go to a GM dealership to obtain it. It would be $$$ but I don't trust ebay or even the local parts store to know what mc goes for the 6x4.

Tandem axle motor homes sometimes also use Hydromax. But I'm not sure if they are 6x4 master cylinders or 4x2. I know I've seen 6x4 motor home mc's in parts lists. But I think they were hydroBoost or some other type. I get Bosch & Bendix confused. One was mostly GM, the other mostly Ford. Both were used on motor homes & buses.

My guess (& this is just speculation without having actually seen one) is the 6x4 Kodiak master cylinder probably only has two outlets like a normal mc. The 8 pistons up front (4 on each side) probably require more fluid than the drum brake wheel cylinders on the rears ... pistons always move more than wheel cylinders.

Other than that, I don't know anymore. I ran across a pdf catalog from some parts supplier that had photos, but I can't find it right now. If I run across it again I'll post the link.

 

[mlwats1@hotmail.com]

there was a company that had a kit that changed the m35 truck to a S cam air brake system the only problem was the kit cost was $6K the kit was too expensive and it didn't stay on the market.

 

[Unforgiven]

Various HydroMax pics

For those who are contemplating a HydroMax conversion, here are some pics of what the booster, master cylinder, and pedal assembly look like:




Upside down pedal


Pedal as it would hang under the dash (from a GMC Topkick)


Self-explanatory


Combination power steering & HydroMax pump from 1998 Topkick C6500. Newer systems use a dedicated pump for the HydroMax.


Booster & master cylinder still bolted together. Notice the low pump pressure switch on the top/firewall side. This senses if there is a problem with the power steering pump. If it senses a hydraulic pump failure or engine loss it is wired to start the emergency backup pump (the round motor on the bottom of the booster)

I have no idea what type of threads are on the master cylinder. I think the brake lines are metric on the newer Chevy's with HydroMax. That's one of the things I have to figure out before I begin my upgrade.

 

[Unforgiven]

There are some crude measurements for you. At least it gives you an idea of what to expect.

Don't hold your breath. I still have to do some research before beginning this upgrade. I have to decide on brake lines, adapters, etc.

I'm even considering leaving the Deuce airpacks on the truck & plumbing them in parallel with the HydroMax. Then an air solenoid could be connected to the Emergency Backup System of the Hydromax.

Why in the world would I do this? Because if I ever had a pump failure then I could have the air packs kick in, pushing, say, 1500 psi for emergency braking. That little HydroMax pump is only good for 500 psi or so. That's hardly enough to stop the truck in a pressing emergency.

As Mudguppy & Jake pointed out, there is a zero bias engineered into the stock Deuce brakes. Theoretically, I should be able to run the rear tandems off of one circuit & the front off the other circuit. Spicergear says otherwise due to 2x the volume required in the rear. He used a single circuit. Still, I'll give it a try first.