M35A2 hydraulic assist steering

[fungus]

Hi all,
In doing some napkin engineering for a DIY pneumatic assist steering torque valve, I ran across this:

Control Valves | Parts Categories | Howe

www.howeperformance.com

Coupled to the appropriate PS pump and cylinder (clamped to the tie rod similar to the M35A3), this could be a very simple hydraulic assist setup. Install would likely be easier than the power steering options out there.
Has anyone tried this? I've reached out to Howe for some specs. Depending on which control valve is necessary, this might be a sub-$1500 setup!

 

[fungus]

I should explain further, these valves are intended to accomplish the same task as the torque valve in the air assist units. They servo the hydraulic control based on the torque measured in the steering shaft. Since this is mechanically coupled from input to output shaft, it would allow you to steer in the event of hydraulic failure (unlike purely hydraulic steering systems). Of course you would have the drag of the cylinder to overcome. What I would do is have two dump valves in series with the hydraulic lines leading to both ends of the cylinder. In the event of a failure, the line pressure could be vented through these (tied to the appropriate big red button on the dash of course).
If you lost a hydraulic line on one side and not the other, you would have to overcome the seals in the cylinder to steer. That's not likely to happen
A rupture disc in each of the vents should keep water/junk out of the system.

 

[rustystud]

That's actually how I'm going to do mine and that's the way someone else here has already done theirs. Sorry cannot remember his name right now. The company I'm using made the steering system on the "MRAP" . Again I cannot remember their name and all my material is in the new shop in some random box waiting to get properly stored. I started my build over 10 years ago. Building new shafts and modifying the steering box. The parts are in boxes waiting for my new shop to be finished.

 

[cbrTodd]

Power Steering Possibility?

Hmm, My M45-530 C TffT. Is fitted with the air assist Pack, And even with the truck full to the brim with water, And at a standstill I can Easily turn the steering either way to squeeze out of the shop on concrete. And at shows or driving in confined places I do like to 'Impress' with that...

steelsoldiers.com

7bdiver is the user name for the member who did something similar. Details on page 7.

 

[fungus]

Wow, thank you, thank you, thank you! That's great that someone else already blazed the trail on this.
I could be completely off, but for a single ram, couldn't you make a bolt-on tang plate rather than welding to the differential? My understanding of the air assist kits is that they were entirely bolt on.
Granted I need to replace shaft seals anyway, so I'll be draining the diff regardless. I get nervous about welding anything in any position other than 1 series, I tend to undercut 2-4 positions unless I'm running TIG.

 

[fungus]

So here's the air assist kit instructions:

Air-O-Matic Air Assist Steering Instructions Scanned Blue Prints 12132493 & 12430289

Air-O-Matic Air Assist Steering Instructions Scanned Blue Prints 12132493 & 12430289 Here are the scanned blue prints and installation instructions for the Air-O-Matic air assist steering. Special Thanks to DavisM38 as he mailed the prints to me so I could scan them and post them here for all...

www.steelsoldiers.com

Thanks very much to the folks who contributed those documents, that helps a lot.
I can definitely see why someone would want to weld that. With the original kit it would have to "waller" around a bit depending on the tolerances of the axle housing and the spring bracket.
Next time I have access to my rig I'll do some measuring and brainstorming to see if I can figure out a way to make a fully constrained clamp on axle bracket.

Rustystud, thank you for your research in the steering box varieties. I'll compare mine to your notes when I have access again. If I arrange a dump valve system for this, it should not place any extra load on the steering box during failure; if I have the weak gearbox casing it would probably be wise to get ahead of the problem anyway.
I started thinking that I should vent those series drains back to the reservoir through large diameter return hose. No sense in harming the salamanders if I don't have to.

 

[fungus]

Other than Eastern Surplus, anyone have good leads on where a guy might come across a good condition 5 ton PS pump?

5-Ton Multi-Fuel Truck Hydraulic Power Steering Pump

5-Ton Multi-Fuel Truck Hydraulic Power Steering Pump Fits M54 Series 5-Ton Trucks with Multi-Fuel Engine

www.easternsurplus.net

 

[ldmack3]

Other than Eastern Surplus, anyone have good leads on where a guy might come across a good condition 5 ton PS pump?

5-Ton Multi-Fuel Truck Hydraulic Power Steering Pump

5-Ton Multi-Fuel Truck Hydraulic Power Steering Pump Fits M54 Series 5-Ton Trucks with Multi-Fuel Engine

www.easternsurplus.net

PUMP POWER STEERING 5TON MULTI FUEL (tnjmurray.com)

 

[fungus]

Thanks ldmack3. Yeebus, by the time you get the adapter mount and gear, that bad boy makes the Eastern Surplus one look cheap.
I'm considering a pump from a Chevy C60 or other midsize dump truck. Gear drive would mean one less belt to keep up, but I can get the C60 pump local for <$100. I'd need to make a bracket. If I run across a power steering multifuel then I could always go that route later.

 

[ldmack3]

Eastern is a take off. TNJ is NOS. Definitely looking like hens teeth. I've had good luck call Big Mike and letting him look for things. Sometimes pricy sometimes only choice. I'm personally not a big fan of take offs.
I've got a belt drive pump and would love to go to a gear driven. But too pricy for me at the moment.

 

[fungus]

I've still been keeping my eyes peeled for a multifuel PS pump that's a bit more budget friendly, may still end up with a belt driven pump.
Does anyone know what the cylinder bore is on the air assist kits? I'm trying to figure up if a 2" hydraulic bore would be sufficient. 3" bore does seem a tad overkill. Knowing the air pressure available and the air assist bore diameter should inform on the force required.

 

[rustystud]

I've still been keeping my eyes peeled for a multifuel PS pump that's a bit more budget friendly, may still end up with a belt driven pump.
Does anyone know what the cylinder bore is on the air assist kits? I'm trying to figure up if a 2" hydraulic bore would be sufficient. 3" bore does seem a tad overkill. Knowing the air pressure available and the air assist bore diameter should inform on the force required.

Remember there is a big difference between "air pressure" and Hydraulic pressure" . A 2" inch ram with 1500 to 2000 PSI would be plenty to power your steering.

 

[fungus]

Just to preserve the information, I found the following while looking at tractor parts:

Control Valves, Cylinder and Steering Cylinders

From what I can tell, these drag link servo valves are mostly intended for aftermarket PS installations on tractors/heavy equipment. Although I did see mention of a F250 that apparently came stock with one?

Personally I'd prefer the torsion servo because it is completely contained in the engine compartment and has all rotary seals. A drag link valve has linear seals and is right in all the road grit/grime. Plus the odds of me getting branches up in the hydraulic lines is pretty high.

 

[fungus]

Remember there is a big difference between "air pressure" and Hydraulic pressure" . A 2" inch ram with 1500 to 2000 PSI would be plenty to power your steering.

I agree completely, I'm just trying to run some numbers.
(Air PSI)*(Air cylinder in^2)=linear force pounds
Which would be a great starting point for the same calculation with a hydraulic ram.
7bdiver used a double-ended hydraulic ram with a 3" bore, granted the rod takes away from that surface area in both directions. That's enough force to bend stuff!

 

[fungus]

Although I can't find the air assist bore diameter, I can do some sanity checks.

Things known:
-Proposed hydraulic cylinder is 2" bore, 1.25" rod.
-Proposed hydraulic pressure should be approximately 1500psi.
-Peak air pressure in my deuce seems to be 90psi.

With those givens, I have a peak hydraulic force during cylinder return of 2872 lbs.

If I propose a 6" air assist cylinder with 0.75 rod, retract force works out to 2505 lbs.
If I bump the air pressure up to 120PSI, this results in 3340 on pull.
A 5" bore with 0.75" rod at 120PSI works out to 2303 lbs.

A 6" bore air cylinder is MASSIVE. The pictures I can find of the cylinder make it look smaller than a 6" bore, but it's hard to tell. It would be great if someone could measure the outer diameter of the air cylinder as a sanity check.

For the proposed hydraulic cylinder, 1.25" diameter rod is a bit overkill and really cuts into the retraction force. I might try to find a cylinder with 2" bore but a slightly smaller rod diameter.

 

[fungus]

They do have a measuring tape in this picture, although it's not perfect it looks to me like maybe 5".

https://www.easternsurplus.net/Documents/Pictures/cropped-2530-01-388-4240%20Air%20Assist%20Power%20Steering%20Upgrade%20Kit%20for%202%20and%20half%20ton%20trucks%20NOS%20(2).JPG