Full Hydraulic Steering

All power steering systems use fluid pressure to help move the front wheels via a steering box.  The next level is to replace your steering box and drag link with a hydraulic ram and control box (orbital valve).  The ram is capable of generating enormous amounts of force making it easy to turn the wheels no matter what their orientation is.  However. this type of steering system is not for everyone.  It has some advantages over a steering box and some big disadvantages.  

Pros:

• Fewer parts in the system to break.  You eliminate the steering box, pitman arm and draglink.

• The front axle placement is now easily changed with no need to move a steering box.

• Due to the steering ram being mounted on the axle, you have full steering no matter how the axle is articulated.  With standard power steering system your steering is limited when your axle articulates due to the angle of the drag link in relation to the pitman arm.

• Steering effort is reduced to almost nothing, even in the rocks.

• Less stress on your frame with the elimination of the steering box.

Cons:

• Not street legal due to there being no mechanical linkage between the steering wheel and front tires.

• Mounting the ram can be complicated.

• Steering stops must be accurate or you can easily damage front end components.

• Care must be taken if you get into a situation where the front end is bound up.

• Depending on the orbital valve you buy, you may not have the ability to steer with the motor off.  There is also less "feel" to the system, so it can be hard to tell if the front end is bound up.

• Price

This article covers some of the stuff I had to do to install a full hydraulic steering system into my rig.  If you must keep your rig street legal, hydraulic assist is a better option, basically you keep your existing power steering system but use a small steering ram to provide additional force. 

The heart of a full hydro steering system is the orbital valve.  This valve takes input from your steering wheel and sends hydraulic fluid to one side of the steering ram or the other, thereby turning your wheels.  There are four ports on this valve, 3 are high pressure and connect to the power steering pump, and the two ports on the ram.  The last port is low pressure (15-20psi typ.) and is the fluid return line.  You'll want to run some sort of cooler and filter, these components should be placed on the fluid return line after the orbital valve but before the reservoir.  I would recommend you mount the orbital valve down where your old power steering box was.  This makes it easier to bleed the system and keeps the high pressure lines out of the passenger compartment.  

I am using a Danfoss orbital valve.  I had Sean Stapley  spec out my valve.  The cylinder stroke (used, not total stroke), bore of the cylinder, pump pressure and flow need to be considered as well as the number of turns lock to lock you desire.  The valve I ended up with is load reactive, so there is some feel to the steering and it has a small pump built into the valve allowing me to turn the wheels if the motor dies.  I highly recommend spending the extra money to get these features as opposed to just pulling a valve from the junkyard.

With the orbital valve mounted where my steering box used to be I had to come up with some sort of adapter to couple the steering shaft and valve.  I ended up modifying the shaft of the orbital valve to accept my u-joint, and made an adapter for the other end that was welded to my steering shaft and pressed into the u-joint.  The original bolts that clamp the u-joint to the shaft are now used to keep both ends from rotating (flats were machined on the adapter and valve shaft). 

I picked up this filter (P/N 7103) and filter mount (P/N 4770) from Napa.  Besides the benefit of filtering the fluid, the filter also adds another 16oz of fluid capacity to the system.  Extra fluid capacity will result in lower fluid temps, the cooler the better. 

Here's a shot of the cooler behind the grill. 3/8 ID lines are used everywhere except between the reservoir and pump (more on that later).

Update - After doing some research on some of the pump problems I was having, I discovered running a cooler was not recommended with a full hydro system.  If a cooler had to be run it is suggested that the fittings be at least a #8 AN fitting to avoid a pressure drop and potential heat generation due to the restriction of the cooler.

I used a 2" bore, 6" stroke steering ram, made by Chief.  This one is the tie rod style, the welded models are a little more compact but you need to be sure of port placement.  With the tie rod models you can turn the ends if you need to move the ports (90 deg increments).  The cylinder was bought from Baileynet.  Single rod cylinders like this are cheap, easy to repair and relatively simple to mount.  Their downside is you will have a different number of turns lock to lock depending on how you mount the cylinder.  This is due to the cylinders shaft displacing some of the fluid inside the body of the cylinder.  Basically one side will always have more fluid than the other and can generate slightly more force.  My system takes roughly 2 turns lock to lock to turn to the right, and 3.8 to turn to the left.  I got used to the difference pretty quickly and it's really only noticeable when driving on the road at higher speeds.  If you really want the same number of turns lock to lock for both directions, you can get a double ended cylinder.  These cylinders are about 7x more expensive and more care must be taken with the way they are mounted since the rods will see more side loads than a single rod cylinder. I won't go into detail on this but when you are determining where to mount the ram you need to actuate the tires in both directions all the way to the steering stops.  You'll notice your tie rod gets closer to the axle towards the end of steering travel.  Take this into account before welding your ram mount to the axle (I speak from experience).  

Mounting the ram,  I wanted the ram above the axle to keep it out of harms way, the 6" stroke cylinder just barely fits, but I had to clearance the bump stop on the drivers side spring plate to make it fit completely.  The pictures above should give you a good idea on how I mounted the ram.  Keep in mind the ram can generate enough force to shear steel, so make the mount big and beefy.