Factory power steering systems are designed for stock vehicles. Adding weight to a truck and/or larger tires increases the force required to steer. Add off-road realities such as low tire pressure and boulders that bookend tires, and the force required to turn the wheels can exceed factory power steering output.
Combining aftermarket wheels with 35-inch tires and a winch-style bumper requires about 60 percent more steering power than stock. Offroad Design (ORD), which specializes in Chevy/GMC fullsize performance, sees 37s as the dividing line where ram assist becomes more necessity than luxury for street/trail 4x4s. In addition to more than doubling the steering force, ram assist also significantly reduces stresses on the steering gearbox, frame, and linkage. Further, the hydraulic cylinder functions as a steering stabilizer, absorbing road irregularities.
Simply adding a ram assist sets off a domino effect in your steering system. The hydraulic cylinder must be adequately fed fluid in both pressure and volume, requiring upstream upgrades.
Steering Gear Box: An aftermarket steering box with two additional ports for the steering ram is required. (Ported Saginaw/Delphi boxes are often upgraded to later-model O-ring ports since rebuildable early inverted-flare-style boxes are scarce.)
Extra Fluid Capacity: The typical OE pump-mounted reservoir doesn’t hold enough fluid to fill the hydraulic cylinder. Even side-hilling at a 45-degree angle can cause fluid starvation in stock pumps that aren’t backed by a larger reservoir. This creates cavitation of the fluid, and the resulting heat kills the pump’s vanes and bearings. Ram-assist cylinders require at least an additional 10 percent fluid volume.
One solution is an aftermarket “longneck” integral reservoir that mounts on the stock-sized pump. A DIY version of this is epoxying a compact, vented puke tank on top of the stock reservoir.
A more popular solution is an aftermarket remote reservoir. Compromises include more plumbing/potential leak points, and farther distance for the fluid to travel. In order for ram-assisted steering to work properly, more than 4 gallons of fluid must circulate every minute. Plumbing in a remote reservoir means more potential constrictions and subsequent compensators, discussed below.
Worst-case scenario is a dead-head condition, where the pump doesn’t receive the minimum fluid flow it needs to run efficiently—impeller energy isn’t transferred out of the pump fast enough, and heat builds up.
On the plus side, aftermarket remote reservoirs also make other variables, such as brake hydro-boosts, easier to plumb. We demonstrate that here with a three-port PSC remote reservoir from ORD (PN SR146K). Further, this particular reservoir has a built-in, replaceable, 35-micron filter, eliminating a common inline link in the fluid-transfer chain. Plus, the added capacity of a reservoir helps keep the steering fluid cooler. Depending on mounting location, the reservoir can also allow the fluid to de-aerate, which prolongs fluid life.
Hose Diameter: ORD recommends plumbing the reservoir with the largest-diameter hose that’s feasible and mounting it as close as possible to, yet still above, the pump. Better flow equals faster steering response. The company’s plumbing kits contain heat- and suction-rated hoses in optimal diameters in addition to AN fittings.
High-Flow Pump: Higher pressure makes fluid flow faster. Stock GM P-pumps typically flow slightly more than 2.0 gallons per minute and have pressure-relief valves that are set somewhere between 1,350 and 1,450 psi. (Pressure builds as the pump spins faster, so the relief/bypass valve prevents hose-overload.) Aftermarket P-pumps run higher pressure. Our example is the PSC SP1405, available from ORD, which pumps up to 1,600 psi in order to circulate about 4.0 gpm of fluid. The pump also has higher-displacement guts to move more fluid. PSC’s bypass valve regulates pressure to what’s needed for the job, up to the high limit. The ram assist doubles the available power, easing demands on the pump.
Cooler: Large metal reservoirs soak up underhood heat. An inline cooler should be added to ensure that the fluid doesn’t exceed 180 degrees and stymie pump life. ORD has several cooler options to work with different vehicle setups. However, we decided to go with a 29,200 BTU B&M Super Cooler, a twin to the truck’s transmission cooler. B&M uses a stacked-plate design that dissipates heat more effectively than fin/tube coolers.
Cylinder Size: Fluid pressure multiplied by piston area equals force. Ergo, higher and larger is more powerful. The required piston stroke for the application can be determined by making a reference mark on the axletube. Then turn the steering wheel to full lock one direction and transfer the mark straight across to the tie rod. Turn full lock the other direction and transfer the axle mark again. Measure mark-to-mark on the tie rod to reveal the required stroke. (Experts such as ORD have already determined the proper cylinders for popular applications.)
Typically, street-driven vehicles use a single-end cylinder. It mounts between the axle and tie rod, retaining the mechanical connection between the steering wheel and steering knuckles.
Various cylinder diameters are available. ORD recommended a 13⁄4-inch cylinder for our full-size Chevy on 37s. While most wheelers don’t believe it is possible to have too much power, ORD’s Stephen Watson mentions a too-much-of-a-good-thing scenario as bad-weather countersteering: The larger the hydraulic cylinder diameter, the longer it takes to reverse direction.
Stepping up to ram assist and adding the other components necessary to make it work properly isn’t cheap. However, wheelers who are running big tires and who aren’t quite ready to take the plunge should have ram assist in the back of their minds for when their existing pumps and boxes die. (We killed a stock pump shortly after installing the ram assist.)