Don't recognize this as an O.E. SS 396 Chevelle steering box? You're right. It's from an '86 Buick Grand National, and it almost bolts right into the B-body. You'll need Lee Engineering press-fit flare-seat inserts (rather than the modern GM O-ring seals) for the hydraulic lines and a special rag-joint steering coupler to make it work in the older chassis.
Few parts have such a direct effect on driving enjoyment and safety as the power-steering gear. While most folks spring for new tie rods and often a new centerlink, the worn-out stock steering gear is lucky to get a fresh coat of detailing paint. At least that's all we'd done on our '70 Chevelle SS 396. The gear looked great in the engine bay, but the power assist came and went as it pleased, usually delivering a heap of assist partway into a turn. This of course, wasn't good in an otherwise well-planned corner-carver suspension.
The exploded views in the Chevy shop manual humbled our thoughts of reviving the steering gear ourselves, so we entrusted it to the experts at Lee Manufacturing in Sun Valley, California. Owner Tom Lee has the great distinction of developing and bestowing the first race-bred power-steering systems on Sprint and Stock cars. From the late '60s through the present, Lee has enough hours of R&D invested in power-steering technology to rival a team of career engineers, and his involvement in current OEM and racing efforts are a testament to his reputation. Although we spec'd a nearly stock rebuild on our steering gear, we'll show some of the options that you might choose if your Chevy sees the track more often than the street. This story won't guide you through a complete rebuild; a factory service manual is invaluable if you're courageous enough to try.
The torsion bar senses the force between the wheels and the driver's hands and allows power assist if there's enough force or road feel. Increasing the diameter of the torsion bar makes it harder to twist, so the driver feels more road-going forces in the wheel before the power assist comes in. The 0.210-inch through 0.285-inch bars are shown front to back in the picture and will generate about 30 lb-in to over 80 lb-in, respectively, of steering effort when installed in a gear.
The compact GM power-steering-gear design has been installed in rear-wheel-drive cars and trucks from 1964 through most of the '90s. That means there's a good chance that a later-model gear will bolt into a muscle-era Chevy with minimal modification. We'd already installed a steering gear from an '86 Buick Grand National (GN) in our Chevelle using Lee's own press-fit flare-seat inserts to make our factory Chevelle hydraulic >> lines work (later GM cars like the GN used O-rings instead of 45-degree flares to seal the hose ends). A special steering coupler (rag joint) is also needed and is available through Lee. Such minute details don't change the scope of this story, but it's important to realize that a later-model gear swap isn't necessarily a 100 percent drop-in replacement.
Here's a sampling of the more common GM piston assemblies. Constant-ratio pistons are on the left, and variable-ratio pistons are on the right. Shown clockwise from lower left, these pistons give ratios of 12:1, 17:1, 20:1, and 16:1. Variable-ratio gears have a numerically higher ratio near center ramping down to a lower ratio near full lock.
With the tired GN gear on the workbench, master tech Julio Valenzuela had it disassembled in a matter of minutes. First impression: This thing was really, really dirty inside, so Valenzuela trash-canned the spent O-rings and seals and bathed the rest in a parts washer. Cleanliness is the name of the game. The cast-iron housing was inspected for cracks and the bore was checked for smoothness; then it was sandblasted and painted. While the paint was drying, Valenzuela laid out the cleaned internals on the bench and began the blueprinting process.